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| − | [[Neurological Examination of Horses Overview]]
| + | #redirect[[:Category:Neurological Examination - Horse]] |
| − | ==Introduction==
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| − | | |
| − | * Investigation of neurological disease combines:
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| − | ** Case history
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| − | ** Neurological examination
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| − | ** Neuroanatomical knowledge
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| − | ** Experience
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| − | | |
| − | ===Aims of Neurological Examination===
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| − | | |
| − | * There are two main aims of neurological examination:
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| − | *# To aid determination of the presence or absence of neurological disease.
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| − | *# To localise the lesion(s) when neurological disease is suspected.
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| − | | |
| − | ===Indications for Neurological Examination===
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| − | | |
| − | * Neurological testing may be indicated by:
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| − | *# '''History'''
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| − | *#* For example, the owner reports a seizure-like episode.
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| − | *# '''Clinical examination'''
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| − | *#* For example, an unexplained area of muscle atrophy or patchy sweating.
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| − | *# '''Information from other tests'''
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| − | *#* Particularly negative, confusing or corroborating evidence from these.
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| − | *#* For example:
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| − | *#** A horse evaluated for pelvic limb lameness that may in fact have a neurological problem.
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| − | *#** A horse with altered mentation or depression that has already been found to have abnormal hepatic function.
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| − | | |
| − | ===Approaches to Neurological Examination===
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| − | | |
| − | * A methodical approach is necessary, whatever the background, to ensure no aspect of examination is omitted.
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| − | * Two different approaches may be taken:
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| − | *# '''Systems based'''
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| − | *#* The different neurological modalities of the systems are examined in turn.
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| − | *# '''Anatomic'''
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| − | *#* Tests are performed in turn working from head to tail.
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| − | * A combination of the two approaches tends to be used in practice.
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| − | | |
| − | ==Neuroanatomy==
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| − | | |
| − | * Certain basic facts must be understood before a decent neurological examination may be performed.
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| − | | |
| − | ===White and Grey Matter===
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| − | | |
| − | * '''White matter''' consists of myelinated axons of nerve cells.
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| − | * '''Grey matter''' is made up of neuronal cell bodies, containing the nucleus.
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| − | | |
| − | ===Afferent and Efferent===
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| − | | |
| − | * '''Afferent''' pathways relay sensory information from receptors towards the spinal cord or brain.
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| − | ** For example:
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| − | *** Touch
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| − | *** Muscle stretch
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| − | *** Vision
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| − | *** Balance
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| − | * '''Efferent''' pathways relay motor or effector information from the brain or spinal cord to muscles or organs.
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| − | | |
| − | ===Motor Neurons and Motor Reflexes===
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| − | | |
| − | * '''Lower motor neurons''' are the last link in the efferent pathway.
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| − | ** Directly innervate skeletal muscles.
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| − | ** Cell bodies are located in the ventral horn of the grey matter of the spinal cord.
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| − | ** Their axons run in peripheral nerves and synapse at the neuromuscular junction.
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| − | * '''Upper motor neurons''' communicate with lower motor neurons.
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| − | ** They:
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| − | *** Relay information to lower motor neurons
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| − | *** Control the output of lower motor neurons.
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| − | ** Upper motor neurons are found in the brain and spinal cord.
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| − | * The term '''reflex''' describes a certain sort of nervous pathway.
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| − | ** The sequence of events in a reflex is as follows:
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| − | **# Signals are derived from receptors.
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| − | **#* For example, tendon stretch.
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| − | **# Signals are conveyed directly in sensory (afferent) fibres.
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| − | **# Afferent signals reach the central nervous system.
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| − | **# Effector signals are generated in the CNS.
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| − | **#* This generally occues via an intermediate neuron, known as the internuncial neuron.
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| − | **# Effector signals are relayed in the lower motor neurons to the muscles.
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| − | ** A reflex does NOT require:
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| − | *** Conscious perception of the stimulus
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| − | *** Ascending or descending upper motor neuron pathways
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| − | *** Ascending or descending proprioceptive pathways
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| − | | |
| − | | |
| − | [[Category:Neurological Examination - Horse]]
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| − | | |
| − | [[Neurological Examination Initial Observation - Horse|A]]
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| − | ==Signalment and History==
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| − | | |
| − | ===Signalment===
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| − | | |
| − | * The term "signalment" describes the animal's age, sex and breed.
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| − | * The horse's signalemt may be relevant to the neurological examination.
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| − | ** For example:
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| − | *** A 1 year old thoroughbred colt with ataxia is more likely to have cervical compression than a space occupying lesion.
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| − | *** An Arabian foal suffering seizures may have idiopathic epilepsy.
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| − | | |
| − | ===History===
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| − | | |
| − | * History is a very important component of the neurological examination.
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| − | ** An owner's description of the animal's behaviour or abnormality may both
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| − | *** Help direct the neurological examonation.
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| − | *** Suggest possible differential diagnoses.
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| − | * For example, a recumbent horse with a history of stumbling or knuckling that has recently fallen:
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| − | ** May have underlying cervical vertebral malformation or stenosis, OR
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| − | ** It is possible that the onset of pelvic limb weakness may have followed a spate of respiratory disease or an abortions, if the animal has [[Herpesviridae|EHV1]] myelitis.
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| − | | |
| − | ==Demeanour/ Behaviour==
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| − | | |
| − | * The horse should be examined from a distance to assess behaviour and demeanour.
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| − | * Diseases associated with altered mentation or behaviour tend to involve the forebrain.
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| − | * Levels of consciousness are determined partly by the cerebrum and partly by the reticular activating system in the brainstem.
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| − | | |
| − | ===What to Look For===
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| − | | |
| − | * Assymetrical changes.
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| − | ** These include:
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| − | *** Circling
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| − | *** Head turning
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| − | ** Horses usually circle or turn towards the affected side.
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| − | * Excessive yawning.
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| − | * Head pressing.
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| − | ** This is often a sign of severe obtundation, which may be caused by:
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| − | *** Diffuse cerebral disease.
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| − | *** Metabolic problems, such as hepatic encephalopathy.
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| − | | |
| − | | |
| − | [[Category:Neurological Examination - Horse|B]]
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| − | | |
| − | ==[[Cranial Nerve Examination - Horse]]==
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| − | | |
| − | * The cranial nerves are numbered 1-12 from the most rostral to the most caudal.
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| − | * A systematic examination of the cranial nerves can aid accurate identification of the site of a lesion.
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| − | | |
| − | ===Cranial Nerve I===
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| − | | |
| − | * Cranial nerve I is the olfactory nerve.
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| − | ** Abnormalities are rarely detected in this nerve.
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| − | | |
| − | ===[[Neurological Eye Examination - Horse]]===
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| − | | |
| − | ====Menace Response====
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| − | | |
| − | * The reflex is assessed by observing the horse blink in response to a visual "threat".
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| − | ** The menace reflex is a learned response.
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| − | * When testing the menace reflex, it should be ensured that the hand does not create air movements.
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| − | ** These may be sensed, for example by the vibrissae, rather than seen.
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| − | * A positive menace reflex confirms normal function of:
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| − | *# The particular optic nerve (CN II)
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| − | *# The optic chiasm
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| − | *#* Nearly all optic nerve fibres cross at the chiasm in the horse.
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| − | *# Pathways through the thalamus to the occipital visual cortex on the opposite side.
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| − | *# Afferent pathways to the facial nerve (VII) nucleus in the brainstem on the original side.
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| − | *#* It is assumed that the afferent pathway from the visual cortex passes through the cerebellum.
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| − | *#** Horses with cerebellar disease may lack or have diminished menace responses.
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| − | *# The facial nerve on the original side (efferent pathway).
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| − | * '''The menace response therefore assesses both visual pathways and the facial nerve.'''
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| − | | |
| − | | |
| − | | |
| − | | |
| − | ====Pupillary Responses====
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| − | | |
| − | * Pupil diameter is controlled by:
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| − | ** Parasympathetic function for constriction.
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| − | *** Occulomotor nerve (CN III)
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| − | ** Sympathetic function for dilation.
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| − | *** For example, in fear or excitement.
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| − | | |
| − | =====The pupillary light reflex (PLR)=====
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| − | | |
| − | * The PLR is a true reflex; the pathways remain in the thalamus and brainstem, and the stimulus need not be perceived.
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| − | * Shining a light into the eye should result in:
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| − | *# A reflex constriction of the pupil in the same eye.
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| − | *#* The direct response
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| − | *# A partial constriction of the other eye.
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| − | *#* The consensual response
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| − | *#* This is difficult to see in large animals because of the shape of the head.
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| − | * The PLR examines:
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| − | ** Optic nerve function
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| − | ** The parasympathetic fibres within the occulomotor nerve.
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| − | | |
| − | =====Horner’s syndrome=====
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| − | | |
| − | * Horner's syndrome is a clinical syndrome caused by damage to the sympathetic nervous system.
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| − | * Signs include:
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| − | ** '''Ptosis'''
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| − | *** Drooping of the upper eyelid
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| − | ** '''Miosis'''
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| − | *** Constriction of the pupil
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| − | ** '''Enophthalmus'''
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| − | *** Sinking of the eyeball into the orbital cavity
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| − | ** '''Protrusion of the third eyelid'''
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| − | ** In horses, Horner's syndrome is often seen in combination with '''regional sweating'''.
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| − | *** Unlike in other animals, sweating in horses is largely dependent on regional increases in blood flow.
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| − | *** Parasympathetic dilation of peripheral blood vessels predominates when sympathetic pathways are interrupted.
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| − | **** This causes regional sweating.
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| − | * The sympathetic supply reaches the eye via the spinal cord; Horner’s syndrome can therefore be caused by spinal cord disease.
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| − | ** First order preganglionic fibres originate in the hypothalamus, and pass via the brainstem and cervical spinal cord to the ventral grey matter of the thoraco-lumbar spinal cord.
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| − | ** Second order preganglionic neurones exit the spinal cord via spinal nerves.
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| − | *** Preganglionic fibres destined for the head leave the spinal cord at spinal nerves T1-T3.
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| − | ** Fibres pass through the thorax, travelling via the cranial stellate ganglion (where they do not synapse), and the vagosympathetic trunk up the neck.
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| − | ** Preganglionic fibres then synapse in the cranial cervical ganglion.
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| − | ** From here, 3rd order postganglionic neurons pass to:
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| − | *** The eye, via branches of the internal carotid artery.
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| − | *** The skin of the top of the head.
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| − | * The sympathetic supply to the skin the neck caudal to C2 is via segmental cervical vertebral nerves.
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| − | ** Cervical vertebral nerves each carry postganglionic sympathetic fibres.
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| − | ** These fibres follow the vertebral artery after leving the stellate ganglion.
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| − | ** A caudal cervical lesion may therefore affect the sypathetic trunk, causing sweating to C2 but not C2-C8.
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| − | *** I.e. C2-C8 has alternative sympathetic supply, and so is not affected by a lesion of this sort.
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| − | * Lesions occuring post- cranial cervical ganglion result in sweating of the face and the area of skin at the base of the ear down to about C1.
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| − | ** For example, lesions in guttural pouch disease.
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| − | | |
| − | | |
| − | | |
| − | | |
| − | ====Vision====
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| − | | |
| − | * The easiest way to determine blindness in horses is to create an obstacle course.
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| − | ** Cover the eyes separately to assess each in turn.
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| − | * Ophthalmological examination should be performed if any any of the followinf are found to be imparied:
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| − | ** Visual pathways
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| − | ** Reflexes
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| − | ** Responses
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| − | | |
| − | ====Eye position====
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| − | | |
| − | * Eye position is controlled by the actions of the extraocular eye muscles.
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| − | ** These muscles are innervated by:
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| − | *** The oculomotor nerve (CN III)
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| − | *** The trochlear nerve (CN IV)
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| − | *** The abducens nerve (CN VI).
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| − | ** '''Dysfunction of these nerves results in strabismus'''.
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| − | * The eyes must move in relation to the position of the head and neck.
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| − | ** Pathways exist that mediate the movement of the eyes in response to head and neck movement.
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| − | *** Vestibular and neck problems can therefore result in a perceived strabismus.
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| − | * Normally, elevation of the head results in ventral movement of the eye.
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| − | ** The eye is usually fixed on a point in space.
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| − | * Lateral head and neck movement results in rhythmic eye movement in response to motion - "doll’s eye vestibular nystagmus".
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| − | ** This is similar to a human fixing its eyes on a point out of a window of a moving train.
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| − | ** This form of nystagmus is normal.
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| − | *** It is characterised by the fast phase being in the direction of movement.
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| − | * Strabismus is relatively easy to asses in the horse due to the elongated shape of the pupil.
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| − | ** True strabismus is relatively rare in horses.
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| − | ** Occulomotor nerve dysfunction may result in lateral deviation of the eyeball.
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| − | *** Parasympathetic supply is often also interrupted, giving mydriasis.
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| − | ** Apparent strabismus may be seen in horses with vestibular disease, since the vestibular system interacts with eye positioning.
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| − | *** However, in this scenario eye movements to and away from the apparent direction of strabismus are still possible.
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| − | | |
| − | | |
| − | [[Category:Neurological Examination - Horse|C]]
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| − | | |
| − | | |
| − | ===[[Face Sensation]]===
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| − | | |
| − | * Nerve fibres giving sensation to the face are carried in cranial nerve V - the trigeminal nerve.
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| − | ** The trigeminal nerve provides sensory innervation to:
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| − | *** The skin of the face
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| − | *** The ears
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| − | *** The nasal mucosa
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| − | *** The cornea
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| − | ** There are three divisions of the trigeminal nerve
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| − | *** The mandibular branch
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| − | *** The maxillary branch
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| − | *** The opthalmic branch
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| − | * Facial sensation is tested by observation for an avoidance response or reflex movement following stimulation.
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| − | ** All the divisions of the trigeminal nerve should be tested. This is achieved by:
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| − | *** Stimulation within the nostrils
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| − | *** Stimulation within the ears
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| − | *** Stimulation between the mandibles
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| − | *** Testing the corneal reflex.
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| − | ***# Pressure is exerted on the corneal surface through the eyelid.
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| − | ***# The opthalmic branch of the trigeminal nerve provides sensory (afferent) input.
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| − | ***# Efferent signals are sent via the abducens nerve (CN VI)
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| − | ***# The retractor oculi muscle retracts the eye
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| − | | |
| − | ====Masticatory muscles====
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| − | | |
| − | * The mandibular branch of the trigeminal nerve carries motor fibres.
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| − | ** It is the only division of the trigeminal nerve that does so.
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| − | * The muscles of mastication are innervated by these fibres.
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| − | ** The masseter and temporalis muscles are particulaly influenced by the mandibular brach of the trigeminal nerve.
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| − | *** These muscles of mastication are also the easiest to assess.
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| − | *** These muscles should be closely examined for signs of atrophy.
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| − | **** '''Atrophy of the temporalis and masseter muscle indicates damage to the mandibular branch of CN V.'''
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| − | | |
| − | ====Facial Expression====
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| − | | |
| − | * The muscles of facial expression are innervated by branches of cranial nerve VII - the facial nerve.
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| − | * The facial nerve also carries the parasympathetic supply to the lacrimal glands.
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| − | ** Horses with facial nerve dysfunction are therefore prone to corneal ulceration, due to :
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| − | *** An inability to blink
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| − | *** Poor or absent tear production
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| − | | |
| − | =====Facial Nerve Dysfunction=====
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| − | | |
| − | * Facial nerve dysfunction is common in the horse.
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| − | * It is readily identified by one or more of the following:
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| − | ** A lip droop
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| − | ** Muzzle deviation
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| − | *** Deviation is towards the normal side.
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| − | ** An ear droop
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| − | * Early or mild dysfunction may be reflected by:
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| − | ** Slight changes to nostril size
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| − | ** Nostril flare
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| − | ** Reduced ear movements in response to audible stimuli
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| − | * The branch of CN VII supplying the muzzle and nostrils crosses the vertical mandibular ramus and the surface of the masseter muscle.
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| − | ** A lesion to that side of the face, for example a kick, may cause signs confined to the nose.
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| − | ** Alternatively, a more central lesion will give both ear and nostril signs.
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| − | | |
| − | =====The Palpebral Reflex=====
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| − | | |
| − | * The palpebral reflex examines the function of both CN V (afferent) and CN VII (efferent).
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| − | * The reflex is elicited by lightly touching the eyelids and watching for reflex closure.
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| − | | |
| − | | |
| − | [[Category:Neurological Examination - Horse|D]]
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| − | | |
| − | ===[[Vestibular System Examination]]===
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| − | | |
| − | ====The Vestibulocochlear Nerve====
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| − | | |
| − | * Cranial nerve VIII is the vestibulocochlear nerve.
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| − | * The vestibulocochlear nerve carries
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| − | ** Auditory, or cochlear, signals.
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| − | ** Balance, or vestibular, signals.
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| − | * Signals from CN VIII are relayed to the vestibular nuclei in the brainstem.
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| − | ** The nuclei in turn relay information to
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| − | *** The eyes
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| − | *** The body and limbs
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| − | *** Higher centres.
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| − | * Many efferent signals are controlled in part by cerebellar input.
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| − | | |
| − | ====Unilateral Vestibular Disease====
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| − | | |
| − | * Horses with unilateral vestibular lesions often have a head tilt towards the side of the lesion.
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| − | * If nystagmus is absent, determining whether a horse with a head tilt is also weak is helpful in deciding whether vestibular disease is central or peripheral.
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| − | ** In peripheral diease, the horse may be ataxic but weakness is not normally seen.
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| − | | |
| − | =====Acute=====
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| − | | |
| − | * In the acute stages of vestibular disease, spontaneous nystagmus may be present.
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| − | ** The appearance of nystagmus is different depending on the type of vestibular disease present.
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| − | *** Central vestibular disease
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| − | **** Nystagmus often is variable; i.e. rotary, horizontal and vertical.
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| − | *** Peripheral vestibular disease
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| − | **** The fast phase of the nystagmus is away from the side of the lesion.
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| − | | |
| − | =====Chronic=====
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| − | | |
| − | * Nystagmus may resolve in more chronic lesions.
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| − | ** However, it may return with changes in head position.
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| − | *** I.e. positional nystagmus.
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| − | * Visual accomodation improves ataxic movements.
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| − | ** However, these may return dramatically on blindfolding.
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| − | | |
| − | ====Bilateral Vestibular Disease====
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| − | | |
| − | * An observable head tilt may not be present.
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| − | * Movements are likely to be markedly ataxic.
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| − | ** This is probably due in part to involvement of ascending proprioceptive and descending motor pathways that run through the brainstem.
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| − | | |
| − | [[Category:Neurological Examination - Horse|E]]
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| − | | |
| − | ===[[Pharyngeal and Laryngeal Function]]===
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| − | | |
| − | * The pharynx and larynx are innervated by:
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| − | ** CN IX - the glossopharyngeal nerve
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| − | ** CN X - the vagus nerve
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| − | ** CN XI - the accessory nerve
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| − | * Pharyngeal and laryngeal function is best studied by:
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| − | *# Observing the horse eat and swallow
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| − | *# Endoscopy
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| − | | |
| − | ====Laryngeal Dysfunction====
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| − | | |
| − | * Left recurrent laryngeal hemiplegia is the most common dysfunction in horses.
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| − | ** The left recurrent laryngeal nerve is a branch of the vagus nerve.
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| − | ** Horses are known as "roarers".
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| − | | |
| − | ====Pharyngeal Dysfunction====
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| − | | |
| − | * Pharyngeal paralysis in horses is commonly associated with peripheral disease.
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| − | ** Especially guttural pouch disease.
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| − | *** Endoscopy of the guttural pouches should be therefore be performed in horses that are dysphagic.
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| − | | |
| − | | |
| − | [[Category:Neurological Examination - Horse|F]]
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| − | | |
| − | | |
| − | ===[[Tongue Movement]] ===
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| − | | |
| − | * The hypoglossal nerve, CN XII provides motor innervation to the [[Tongue - Anatomy & Physiology|tongue]].
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| − | * Normally, a horse resists the [[Tongue - Anatomy & Physiology|tongue]] being retracted from the mouth.
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| − | ** The horse will quickly return the tongue after it is pulled out to the side.
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| − | * Horses with hypoglossal weakness appear differently.
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| − | ** The [[Tongue - Anatomy & Physiology|tongue]] may protrude from the mouth.
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| − | ** Chronic unilateral hypoglossal lesions may result in unilateral tongue atrophy.
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| − | ** Bilateral hypoglossal lesions may result in difficulty prehending food.
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| − | * Horses with cerebral dysfunction may have signs corresponding to tongue weakness.
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| − | ** However, [[Tongue - Anatomy & Physiology|tongue]] atrophy is not present in these animals.
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| − | | |
| − | | |
| − | [[Category:Neurological Examination - Horse|G]]
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| − | | |
| − | | |
| − | ==[[Body, Spinal Cord and Limb Neurological Examination - Horse]]==
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| − | | |
| − | ===Conscious Proprioception Testing ===
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| − | | |
| − | * It is possible to test a horse’s conscious proprioception by altering the position of the limbs in space.
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| − | ** Horses should normally replace their limbs to the normal position within a few seconds.
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| − | *** There is a degress of individual variability, however, and the test can be difficult to interpret.
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| − | * Tests can also be performed by walking or trotting a horse and then suddenly stopping.
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| − | ** The animal should be observed to see how quickly it replaces its legs in a normal position.
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| − | | |
| − | ===Gait===
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| − | | |
| − | * Gait is a combination of higher control of motor function and unconscious proprioception.
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| − | * During assessment of gait, the examiner is looking primarily for evidence of '''ataxia''' and/ or '''weakness'''.
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| − | ** Each leg should be assessed in turn.
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| − | * Defects may be graded on a five-point scale (the Mayhew scale).
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| − | ** 0 is normal and 5 is recumbent.
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| − | | |
| − | ====Ataxia====
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| − | | |
| − | * Defects in unconscious proprioceptive pathways result in ataxia.
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| − | ** These pathways originate in muscle spindle stretch receptors and golgi tendon organs.
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| − | ** Impulses are relayed via peripheral nerves to the spinal cord.
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| − | ** Signals then ascend in pathways to the cerebellum.
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| − | *** Primary cerebellar diseases in horses are rare, but classically cause incoordination of the head and limbs.
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| − | **** Weakness is not a prominent feature.
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| − | **** The cerebellum communicates with the vestibular nuclei, and so cerebellar diseases may sometimes present with vestibular signs.
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| − | * Manifestations of ataxia:
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| − | ** Exaggerated movements - hypermetria
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| − | ** Reduced movements - stilted hypometric movements
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| − | ** Both exaggerated and reduced movements - dysmetria.
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| − | * Animals may also
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| − | ** Sway
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| − | ** Place their feet abnormally
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| − | *** Horses cross or weave their feet, with abnormal abduction or adduction.
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| − | * Signs of spinal ataxia may be exaggerated by lifting the horse's head.
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| − | ** This is beacuse it removes the horizon.
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| − | ** Similar responses can be generated by walking up and down slopes.
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| − | * Circling the horse can also reveal ataxia.
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| − | ** The horse may plant its feet and rotate around them without placing them properly.
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| − | ** Outward rotation of the pelvic limbs is also a common sign.
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| − | *** The term for this is "circumduction".
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| − | * Unconscious proprioception may also be tested by backing the horse.
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| − | ** Normal horses back with a diagonal gait.
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| − | ** Horses with spinal ataxia will often pace when backing.
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| − | | |
| − | ====Weakness====
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| − | | |
| − | * Weakness usually manifests as toe dragging, stumbling, or knuckling over.
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| − | ** It is a good idea to look closely at the horse’s hooves to see if any are abnormally worn.
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| − | * Weakness may be caused by dysfunction of either the upper or lower motorneurons.
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| − | ** Lower motor neuron weakness.
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| − | *** Accompanied by:
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| − | **** Muscle flaccidity
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| − | **** Muscle atrophy if chronic
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| − | *** May sometimes appear similar to lameness.
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| − | ** Upper motor neuron weakness.
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| − | *** Presents as a lack of control of limb muscle movement.
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| − | *** Tested most easily tested by pulling the tail during walking.
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| − | **** Pulling the tail while stationary probably primarily tests lower motor neuron control and muscular strength of the pelvic limb.
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| − | [[Category:Neurological Examination - Horse]]
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| − | | |
| − | | |
| − | ==[[Site of Spinal Lesions Determination - Horse]]==
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| − | | |
| − | * If there are no brain or brainstem signs, an animal with ataxia or weakness is most likely to have a lesion in the spinal cord.
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| − | * The spinal reflexes used in small animals to assess specific segments are not very useful in adult horses.
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| − | ** However, withdrawal reflexes are useful in recumbent horses with severe lesions.
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| − | *** A stimulus is applied to the distal limb and the reflex results in limb withdrawal.
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| − | | |
| − | ===Cervical Lesions===
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| − | | |
| − | * Cervical lesions occur from C1 to C5
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| − | ** C6 and C7 may also be included.
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| − | * Horses with defects in all four legs are most likely to have a cervical lesion.
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| − | * The pelvic limbs tend to be more severely affected than the thoracic limbs.
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| − | ** This is due to the topographical arrangement of the white matter tracts in the spinal cord.
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| − | | |
| − | ====Effects on Reflexes====
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| − | | |
| − | * Cervicofacial reflex
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| − | ** The cervicofacial reflex is tested by lightly stimulating the skin of the lateral neck.
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| − | *** In an intact reflex movement of the lips should be observed.
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| − | *** This reflex varies widely between individual horses.
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| − | *** This is not intact in cervical lesions.
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| − | * Withdrawal reflexes
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| − | ** Only of use in recumbent horses.
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| − | ** In cervical lesions, reflexes in both thoracic and pelvic limbs may be exaggerated.
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| − | *** This is due to a loss of upper motor neuron inhibition.
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| − | | |
| − | ===Brachial Lesions===
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| − | | |
| − | * Brachial lesions occur from C6 to T2.
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| − | * Signs of a spinal lesion at this level differ in the thoracic and pelvic limbs.
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| − | ** Thoracic limbs
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| − | *** Lower motor neuron signs
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| − | **** Weakness
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| − | ***** May be mild
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| − | ***** May manifest unwillingness to take the weight on the other thoracic limb when one is picked up.
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| − | **** Muscle atrophy
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| − | *** Withdrawal reflex in recumbent animals may be reduced.
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| − | ** Pelvic limbs
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| − | *** Ataxia
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| − | *** Upper motor neuon weakness
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| − | **** For example, swaying and stumbling.
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| − | *** Withdrawal reflex in recumbent animals may be exaggerated.
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| − | | |
| − | ===Thoraco-lumbar Lesions===
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| − | | |
| − | * Thoraco-lumbar lesions occur in the segments T3 to L3 of the spinal cord.
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| − | * In an animal that has pelvic limb ataxia and weakness but no thoracic limb involvement, the lesion will be between T2 and L3.
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| − | ** I.e. caudal to the brachial plexus.
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| − | ** The animal should be closely examined for symmetry over the gluteals and pelvic limbs.
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| − | *** If there is symmetry, the lesion is likely to be at this level.
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| − | *** If there is no symmetry, the lesion is likely to be more caudal, and involve the pelvic outflow.
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| − | * Asymmetry may be detected in the cutaneous trunic reflex.
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| − | ** This is tested by lightly stimulating the skin of the lateral thorax.
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| − | * The withdrawal reflex in the pelvic limb may be exaggerated.
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| − | * Flexibility of the thoracolumbar spine may be assessed.
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| − | ** The skin of the longissimus musculature is firmly stimulated, and observed for:
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| − | *** A lordotic movement over the thorax and cranial lumbar region, and
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| − | *** A kyphotic movement over the caudal lumbar region and gluteals.
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| − | | |
| − | ===Lumbosacral Lesions===
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| − | | |
| − | * Lumbosacral lesions occur between the segments L4 and S3.
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| − | * Horses with such lesions may:
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| − | ** Exhibit atrophy of one or more muscles of the pelvic region, and so
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| − | ** Be easy to pull over when standing, and
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| − | ** Be unwilling or unable to take weight on the affected side when the other limb is lifted.
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| − | * More caudal lesions may:
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| − | ** Affect the anal and perineal reflexes.
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| − | *** These are tested by lightly stimulating the skin surrounding the anus and observing for a reflex contraction of the anal sphincter.
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| − | ** Cause paresis of the tail.
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| − | * The withdrawal reflex may be reduced or absent in the pelvic limb.
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| − | | |
| − | ===Sacral Lesions===
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| − | | |
| − | * Damage to the savral spinal cord can affect bladder function and control of defaecation.
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| − | | |
| − | ====Bladder Incontinence====
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| − | | |
| − | * The bladder is reflexely controlled, via higher order neurones in the caudal brainstem and cerebrum, by the:
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| − | ** Pelvic nerve
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| − | *** Parasympathetic fibres leave the spinal cord in the sacral segments and combine to form the pelvic nerve.
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| − | **** These fibres innervate the smooth detrusor muscle of the bladder wall.
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| − | ** Pudendal nerve
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| − | *** The pudendal nerve innervates the striated muscle of the bladder neck.
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| − | * During micturition, the bladder is evacuated as:
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| − | ** The striated muscle is relaxed.
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| − | ** Stimulation of the pelvic nerve causes the detrusor smooth muscle to contract.
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| − | | |
| − | ====Faecal Incompetence====
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| − | | |
| − | * Lesions in the sacral region may also be manifest as faecal incompetence.
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| − | ** In horses, problems are usually caused by defects in the lower motor neurons in the pelvic nerve.
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| − | *** Faeces is retained.
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| − | | |
| − | [[Category:Neurological Examination - Horse]]
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