Line 7: |
Line 7: |
| }} | | }} |
| <br> | | <br> |
| + | ==Introduction== |
| + | |
| + | * Investigation of neurological disease combines: |
| + | ** Case history |
| + | ** Neurological examination |
| + | ** Neuroanatomical knowledge |
| + | ** Experience |
| + | |
| + | ===Aims of Neurological Examination=== |
| + | |
| + | * There are two main aims of neurological examination: |
| + | *# To aid determination of the presence or absence of neurological disease. |
| + | *# To localise the lesion(s) when neurological disease is suspected. |
| + | |
| + | ===Indications for Neurological Examination=== |
| + | |
| + | * Neurological testing may be indicated by: |
| + | *# '''History''' |
| + | *#* For example, the owner reports a seizure-like episode. |
| + | *# '''Clinical examination''' |
| + | *#* For example, an unexplained area of muscle atrophy or patchy sweating. |
| + | *# '''Information from other tests''' |
| + | *#* Particularly negative, confusing or corroborating evidence from these. |
| + | *#* For example: |
| + | *#** A horse evaluated for pelvic limb lameness that may in fact have a neurological problem. |
| + | *#** A horse with altered mentation or depression that has already been found to have abnormal hepatic function. |
| + | |
| + | ===Approaches to Neurological Examination=== |
| + | |
| + | * A methodical approach is necessary, whatever the background, to ensure no aspect of examination is omitted. |
| + | * Two different approaches may be taken: |
| + | *# '''Systems based''' |
| + | *#* The different neurological modalities of the systems are examined in turn. |
| + | *# '''Anatomic''' |
| + | *#* Tests are performed in turn working from head to tail. |
| + | * A combination of the two approaches tends to be used in practice. |
| + | |
| + | ==Neuroanatomy== |
| + | |
| + | * Certain basic facts must be understood before a decent neurological examination may be performed. |
| + | |
| + | ===White and Grey Matter=== |
| + | |
| + | * '''White matter''' consists of myelinated axons of nerve cells. |
| + | * '''Grey matter''' is made up of neuronal cell bodies, containing the nucleus. |
| + | |
| + | ===Afferent and Efferent=== |
| + | |
| + | * '''Afferent''' pathways relay sensory information from receptors towards the spinal cord or brain. |
| + | ** For example: |
| + | *** Touch |
| + | *** Muscle stretch |
| + | *** Vision |
| + | *** Balance |
| + | * '''Efferent''' pathways relay motor or effector information from the brain or spinal cord to muscles or organs. |
| + | |
| + | ===Motor Neurons and Motor Reflexes=== |
| + | |
| + | * '''Lower motor neurons''' are the last link in the efferent pathway. |
| + | ** Directly innervate skeletal muscles. |
| + | ** Cell bodies are located in the ventral horn of the grey matter of the spinal cord. |
| + | ** Their axons run in peripheral nerves and synapse at the neuromuscular junction. |
| + | * '''Upper motor neurons''' communicate with lower motor neurons. |
| + | ** They: |
| + | *** Relay information to lower motor neurons |
| + | *** Control the output of lower motor neurons. |
| + | ** Upper motor neurons are found in the brain and spinal cord. |
| + | * The term '''reflex''' describes a certain sort of nervous pathway. |
| + | ** The sequence of events in a reflex is as follows: |
| + | **# Signals are derived from receptors. |
| + | **#* For example, tendon stretch. |
| + | **# Signals are conveyed directly in sensory (afferent) fibres. |
| + | **# Afferent signals reach the central nervous system. |
| + | **# Effector signals are generated in the CNS. |
| + | **#* This generally occues via an intermediate neuron, known as the internuncial neuron. |
| + | **# Effector signals are relayed in the lower motor neurons to the muscles. |
| + | ** A reflex does NOT require: |
| + | *** Conscious perception of the stimulus |
| + | *** Ascending or descending upper motor neuron pathways |
| + | *** Ascending or descending proprioceptive pathways |
| + | |
| + | ==Signalment and History== |
| + | |
| + | ===Signalment=== |
| + | |
| + | * The term "signalment" describes the animal's age, sex and breed. |
| + | * The horse's signalemt may be relevant to the neurological examination. |
| + | ** For example: |
| + | *** A 1 year old thoroughbred colt with ataxia is more likely to have cervical compression than a space occupying lesion. |
| + | *** An Arabian foal suffering seizures may have idiopathic epilepsy. |
| + | |
| + | ===History=== |
| + | |
| + | * History is a very important component of the neurological examination. |
| + | ** An owner's description of the animal's behaviour or abnormality may both |
| + | *** Help direct the neurological examonation. |
| + | *** Suggest possible differential diagnoses. |
| + | * For example, a recumbent horse with a history of stumbling or knuckling that has recently fallen: |
| + | ** May have underlying cervical vertebral malformation or stenosis, OR |
| + | ** 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. |
| + | |
| + | ==Demeanour/ Behaviour== |
| + | |
| + | * The horse should be examined from a distance to assess behaviour and demeanour. |
| + | * Diseases associated with altered mentation or behaviour tend to involve the forebrain. |
| + | * Levels of consciousness are determined partly by the cerebrum and partly by the reticular activating system in the brainstem. |
| + | |
| + | ===What to Look For=== |
| + | |
| + | * Assymetrical changes. |
| + | ** These include: |
| + | *** Circling |
| + | *** Head turning |
| + | ** Horses usually circle or turn towards the affected side. |
| + | * Excessive yawning. |
| + | * Head pressing. |
| + | ** This is often a sign of severe obtundation, which may be caused by: |
| + | *** Diffuse cerebral disease. |
| + | *** Metabolic problems, such as hepatic encephalopathy. |
| + | |
| + | ==Cranial Nerve Examination== |
| + | |
| + | * The cranial nerves are numbered 1-12 from the most rostral to the most caudal. |
| + | * A systematic examination of the cranial nerves can aid accurate identification of the site of a lesion. |
| + | |
| + | ===Cranial Nerve I=== |
| + | |
| + | * Cranial nerve I is the olfactory nerve. |
| + | ** Abnormalities are rarely detected in this nerve. |
| + | |
| + | ===Eyes=== |
| + | |
| + | ====Menace Response==== |
| + | |
| + | * The reflex is assessed by observing the horse blink in response to a visual "threat". |
| + | ** The menace reflex is a learned response. |
| + | * When testing the menace reflex, it should be ensured that the hand does not create air movements. |
| + | ** These may be sensed, for example by the vibrissae, rather than seen. |
| + | * A positive menace reflex confirms normal function of: |
| + | *# The particular optic nerve (CN II) |
| + | *# The optic chiasm |
| + | *#* Nearly all optic nerve fibres cross at the chiasm in the horse. |
| + | *# Pathways through the thalamus to the occipital visual cortex on the opposite side. |
| + | *# Afferent pathways to the facial nerve (VII) nucleus in the brainstem on the original side. |
| + | *#* It is assumed that the afferent pathway from the visual cortex passes through the cerebellum. |
| + | *#** Horses with cerebellar disease may lack or have diminished menace responses. |
| + | *# The facial nerve on the original side (efferent pathway). |
| + | * '''The menace response therefore assesses both visual pathways and the facial nerve.''' |
| + | |
| + | ====Pupillary responses==== |
| + | |
| + | * Pupil diameter is controlled by: |
| + | ** Parasympathetic function for constriction. |
| + | *** Occulomotor nerve (CN III) |
| + | ** Sympathetic function for dilation. |
| + | *** For example, in fear or excitement. |
| + | |
| + | =====The pupillary light reflex (PLR)===== |
| + | |
| + | * The PLR is a true reflex; the pathways remain in the thalamus and brainstem, and the stimulus need not be perceived. |
| + | * Shining a light into the eye should result in: |
| + | *# A reflex constriction of the pupil in the same eye. |
| + | *#* The direct response |
| + | *# A partial constriction of the other eye. |
| + | *#* The consensual response |
| + | *#* This is difficult to see in large animals because of the shape of the head. |
| + | * The PLR examines: |
| + | ** Optic nerve function |
| + | ** The parasympathetic fibres within the occulomotor nerve. |
| + | |
| + | =====Horner’s syndrome===== |
| + | |
| + | * Horner's syndrome is a clinical syndrome caused by damage to the sympathetic nervous system. |
| + | * Signs include: |
| + | ** '''Ptosis''' |
| + | *** Drooping of the upper eyelid |
| + | ** '''Miosis''' |
| + | *** Constriction of the pupil |
| + | ** '''Enophthalmus''' |
| + | *** Sinking of the eyeball into the orbital cavity |
| + | ** '''Protrusion of the third eyelid''' |
| + | ** In horses, Horner's syndrome is often seen in combination with '''regional sweating'''. |
| + | *** Unlike in other animals, sweating in horses is largely dependent on regional increases in blood flow. |
| + | *** Parasympathetic dilation of peripheral blood vessels predominates when sympathetic pathways are interrupted. |
| + | **** This causes regional sweating. |
| + | * The sympathetic supply reaches the eye via the spinal cord; Horner’s syndrome can therefore be caused by spinal cord disease. |
| + | ** 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. |
| + | ** Second order preganglionic neurones exit the spinal cord via spinal nerves. |
| + | *** Preganglionic fibres destined for the head leave the spinal cord at spinal nerves T1-T3. |
| + | ** Fibres pass through the thorax, travelling via the cranial stellate ganglion (where they do not synapse), and the vagosympathetic trunk up the neck. |
| + | ** Preganglionic fibres then synapse in the cranial cervical ganglion. |
| + | ** From here, 3rd order postganglionic neurons pass to: |
| + | *** The eye, via branches of the internal carotid artery. |
| + | *** The skin of the top of the head. |
| + | * The sympathetic supply to the skin the neck caudal to C2 is via segmental cervical vertebral nerves. |
| + | ** Cervical vertebral nerves each carry postganglionic sympathetic fibres. |
| + | ** These fibres follow the vertebral artery after leving the stellate ganglion. |
| + | ** A caudal cervical lesion may therefore affect the sypathetic trunk, causing sweating to C2 but not C2-C8. |
| + | *** I.e. C2-C8 has alternative sympathetic supply, and so is not affected by a lesion of this sort. |
| + | * 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. |
| + | ** For example, lesions in guttural pouch disease. |
| + | |
| + | ====Vision==== |
| + | |
| + | * The easiest way to determine blindness in horses is to create an obstacle course. |
| + | ** Cover the eyes separately to assess each in turn. |
| + | * Ophthalmological examination should be performed if any any of the followinf are found to be imparied: |
| + | ** Visual pathways |
| + | ** Reflexes |
| + | ** Responses |
| + | |
| + | ====Eye position==== |
| + | |
| + | * Eye position is controlled by the actions of the extraocular eye muscles. |
| + | ** These muscles are innervated by: |
| + | *** The oculomotor nerve (CN III) |
| + | *** The trochlear nerve (CN IV) |
| + | *** The abducens nerve (CN VI). |
| + | ** '''Dysfunction of these nerves results in strabismus'''. |
| + | * The eyes must move in relation to the position of the head and neck. |
| + | ** Pathways exist that mediate the movement of the eyes in response to head and neck movement. |
| + | *** Vestibular and neck problems can therefore result in a perceived strabismus. |
| + | * Normally, elevation of the head results in ventral movement of the eye. |
| + | ** The eye is usually fixed on a point in space. |
| + | * Lateral head and neck movement results in rhythmic eye movement in response to motion - "doll’s eye vestibular nystagmus". |
| + | ** This is similar to a human fixing its eyes on a point out of a window of a moving train. |
| + | ** This form of nystagmus is normal. |
| + | *** It is characterised by the fast phase being in the direction of movement. |
| + | * Strabismus is relatively easy to asses in the horse due to the elongated shape of the pupil. |
| + | ** True strabismus is relatively rare in horses. |
| + | ** Occulomotor nerve dysfunction may result in lateral deviation of the eyeball. |
| + | *** Parasympathetic supply is often also interrupted, giving mydriasis. |
| + | ** Apparent strabismus may be seen in horses with vestibular disease, since the vestibular system interacts with eye positioning. |
| + | *** However, in this scenario eye movements to and away from the apparent direction of strabismus are still possible. |
| + | |
| + | ===Sensation to the Face=== |
| + | |
| + | * Nerve fibres giving sensation to the face are carried in cranial nerve V - the trigeminal nerve. |
| + | ** The trigeminal nerve provides sensory innervation to: |
| + | *** The skin of the face |
| + | *** The ears |
| + | *** The nasal mucosa |
| + | *** The cornea |
| + | ** There are three divisions of the trigeminal nerve |
| + | *** The mandibular branch |
| + | *** The maxillary branch |
| + | *** The opthalmic branch |
| + | * Facial sensation is tested by observation for an avoidance response or reflex movement following stimulation. |
| + | ** All the divisions of the trigeminal nerve should be tested. This is achieved by: |
| + | *** Stimulation within the nostrils |
| + | *** Stimulation within the ears |
| + | *** Stimulation between the mandibles |
| + | *** Testing the corneal reflex. |
| + | ***# Pressure is exerted on the corneal surface through the eyelid. |
| + | ***# The opthalmic branch of the trigeminal nerve provides sensory (afferent) input. |
| + | ***# Efferent signals are sent via the abducens nerve (CN VI) |
| + | ***# The retractor oculi muscle retracts the eye |
| + | |
| + | ====Masticatory muscles==== |
| + | |
| + | * The mandibular branch of the trigeminal nerve carries motor fibres. |
| + | ** It is the only division of the trigeminal nerve that does so. |
| + | * The muscles of mastication are innervated by these fibres. |
| + | ** The masseter and temporalis muscles are particulaly influenced by the mandibular brach of the trigeminal nerve. |
| + | *** These muscles of mastication are also the easiest to assess. |
| + | *** These muscles should be closely examined for signs of atrophy. |
| + | **** '''Atrophy of the temporalis and masseter muscle indicates damage to the mandibular branch of CN V.''' |
| + | |
| + | ====Facial Expression==== |
| + | |
| + | * The muscles of facial expression are innervated by branches of cranial nerve VII - the facial nerve. |
| + | * The facial nerve also carries the parasympathetic supply to the lacrimal glands. |
| + | ** Horses with facial nerve dysfunction are therefore prone to corneal ulceration, due to : |
| + | *** An inability to blink |
| + | *** Poor or absent tear production |
| + | |
| + | =====Facial Nerve Dysfunction===== |
| + | |
| + | * Facial nerve dysfunction is common in the horse. |
| + | * It is readily identified by one or more of the following: |
| + | ** A lip droop |
| + | ** Muzzle deviation |
| + | *** Deviation is towards the normal side. |
| + | ** An ear droop |
| + | * Early or mild dysfunction may be reflected by: |
| + | ** Slight changes to nostril size |
| + | ** Nostril flare |
| + | ** Reduced ear movements in response to audible stimuli |
| + | * The branch of CN VII supplying the muzzle and nostrils crosses the vertical mandibular ramus and the surface of the masseter muscle. |
| + | ** A lesion to that side of the face, for example a kick, may cause signs confined to the nose. |
| + | ** Alternatively, a more central lesion will give both ear and nostril signs. |
| + | |
| + | =====The Palpebral Reflex===== |
| + | |
| + | * The palpebral reflex examines the function of both CN V (afferent) and CN VII (efferent). |
| + | * The reflex is elicited by lightly touching the eyelids and watching for reflex closure. |
| + | |
| + | ===The Vestibular System=== |
| + | |
| + | ====The Vestibulocochlear Nerve==== |
| + | |
| + | * Cranial nerve VIII is the vestibulocochlear nerve. |
| + | * The vestibulocochlear nerve carries |
| + | ** Auditory, or cochlear, signals. |
| + | ** Balance, or vestibular, signals. |
| + | * Signals from CN VIII are relayed to the vestibular nuclei in the brainstem. |
| + | ** The nuclei in turn relay information to |
| + | *** The eyes |
| + | *** The body and limbs |
| + | *** Higher centres. |
| + | * Many efferent signals are controlled in part by cerebellar input. |
| + | |
| + | ====Unilateral Vestibular Disease==== |
| + | |
| + | * Horses with unilateral vestibular lesions often have a head tilt towards the side of the lesion. |
| + | * 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. |
| + | ** In peripheral diease, the horse may be ataxic but weakness is not normally seen. |
| + | |
| + | =====Acute===== |
| + | |
| + | * In the acute stages of vestibular disease, spontaneous nystagmus may be present. |
| + | ** The appearance of nystagmus is different depending on the type of vestibular disease present. |
| + | *** Central vestibular disease |
| + | **** Nystagmus often is variable; i.e. rotary, horizontal and vertical. |
| + | *** Peripheral vestibular disease |
| + | **** The fast phase of the nystagmus is away from the side of the lesion. |
| + | |
| + | =====Chronic===== |
| + | |
| + | * Nystagmus may resolve in more chronic lesions. |
| + | ** However, it may return with changes in head position. |
| + | *** I.e. positional nystagmus. |
| + | * Visual accomodation improves ataxic movements. |
| + | ** However, these may return dramatically on blindfolding. |
| + | |
| + | ====Bilateral Vestibular Disease==== |
| + | |
| + | * An observable head tilt may not be present. |
| + | * Movements are likely to be markedly ataxic. |
| + | ** This is probably due in part to involvement of ascending proprioceptive and descending motor pathways that run through the brainstem. |
| + | |
| + | ===Pharyngeal and Laryngeal Function=== |
| + | |
| + | * The pharynx and larynx are innervated by: |
| + | ** CN IX - the glossopharyngeal nerve |
| + | ** CN X - the vagus nerve |
| + | ** CN XI - the accessory nerve |
| + | * Pharyngeal and laryngeal function is best studied by: |
| + | *# Observing the horse eat and swallow |
| + | *# Endoscopy |
| + | |
| + | ====Laryngeal Dysfunction==== |
| + | |
| + | * Left recurrent laryngeal hemiplegia is the most common dysfunction in horses. |
| + | ** The left recurrent laryngeal nerve is a branch of the vagus nerve. |
| + | ** Horses are known as "roarers". |
| + | |
| + | ====Pharyngeal Dysfunction==== |
| + | |
| + | * Pharyngeal paralysis in horses is commonly associated with peripheral disease. |
| + | ** Especially guttural pouch disease. |
| + | *** Endoscopy of the guttural pouches should be therefore be performed in horses that are dysphagic. |
| + | |
| + | ===Movement of the Tongue=== |
| + | |
| + | * The hypoglossal nerve, CN XII provides motor innervation to the [[Oral Cavity - Tongue - Anatomy & Physiology|tongue]]. |
| + | * Normally, a horse resists the [[Oral Cavity - Tongue - Anatomy & Physiology|tongue]] being retracted from the mouth. |
| + | ** The horse will quickly return the tongue after it is pulled out to the side. |
| + | * Horses with hypoglossal weakness appear differently. |
| + | ** The [[Oral Cavity - Tongue - Anatomy & Physiology|tongue]] may protrude from the mouth. |
| + | ** Chronic unilateral hypoglossal lesions may result in unilateral tongue atrophy. |
| + | ** Bilateral hypoglossal lesions may result in difficulty prehending food. |
| + | * Horses with cerebral dysfunction may have signs corresponding to tongue weakness. |
| + | ** However, [[Oral Cavity - Tongue - Anatomy & Physiology|tongue]] atrophy is not present in these animals. |
| + | |
| + | ==The Body, Spinal Cord and Limbs== |
| + | |
| + | ===Testing Conscious Proprioception=== |
| + | |
| + | * It is possible to test a horse’s conscious proprioception by altering the position of the limbs in space. |
| + | ** Horses should normally replace their limbs to the normal position within a few seconds. |
| + | *** There is a degress of individual variability, however, and the test can be difficult to interpret. |
| + | * Tests can also be performed by walking or trotting a horse and then suddenly stopping. |
| + | ** The animal should be observed to see how quickly it replaces its legs in a normal position. |
| + | |
| + | ===Gait=== |
| + | |
| + | * Gait is a combination of higher control of motor function and unconscious proprioception. |
| + | * During assessment of gait, the examiner is looking primarily for evidence of '''ataxia''' and/ or '''weakness'''. |
| + | ** Each leg should be assessed in turn. |
| + | * Defects may be graded on a five-point scale (the Mayhew scale). |
| + | ** 0 is normal and 5 is recumbent. |
| + | |
| + | ====Ataxia==== |
| + | |
| + | * Defects in unconscious proprioceptive pathways result in ataxia. |
| + | ** These pathways originate in muscle spindle stretch receptors and golgi tendon organs. |
| + | ** Impulses are relayed via peripheral nerves to the spinal cord. |
| + | ** Signals then ascend in pathways to the cerebellum. |
| + | *** Primary cerebellar diseases in horses are rare, but classically cause incoordination of the head and limbs. |
| + | **** Weakness is not a prominent feature. |
| + | **** The cerebellum communicates with the vestibular nuclei, and so cerebellar diseases may sometimes present with vestibular signs. |
| + | * Manifestations of ataxia: |
| + | ** Exaggerated movements - hypermetria |
| + | ** Reduced movements - stilted hypometric movements |
| + | ** Both exaggerated and reduced movements - dysmetria. |
| + | * Animals may also |
| + | ** Sway |
| + | ** Place their feet abnormally |
| + | *** Horses cross or weave their feet, with abnormal abduction or adduction. |
| + | * Signs of spinal ataxia may be exaggerated by lifting the horse's head. |
| + | ** This is beacuse it removes the horizon. |
| + | ** Similar responses can be generated by walking up and down slopes. |
| + | * Circling the horse can also reveal ataxia. |
| + | ** The horse may plant its feet and rotate around them without placing them properly. |
| + | ** Outward rotation of the pelvic limbs is also a common sign. |
| + | *** The term for this is "circumduction". |
| + | * Unconscious proprioception may also be tested by backing the horse. |
| + | ** Normal horses back with a diagonal gait. |
| + | ** Horses with spinal ataxia will often pace when backing. |
| + | |
| + | ====Weakness==== |
| + | |
| + | * Weakness usually manifests as toe dragging, stumbling, or knuckling over. |
| + | ** It is a good idea to look closely at the horse’s hooves to see if any are abnormally worn. |
| + | * Weakness may be caused by dysfunction of either the upper or lower motorneurons. |
| + | ** Lower motor neuron weakness. |
| + | *** Accompanied by: |
| + | **** Muscle flaccidity |
| + | **** Muscle atrophy if chronic |
| + | *** May sometimes appear similar to lameness. |
| + | ** Upper motor neuron weakness. |
| + | *** Presents as a lack of control of limb muscle movement. |
| + | *** Tested most easily tested by pulling the tail during walking. |
| + | **** Pulling the tail while stationary probably primarily tests lower motor neuron control and muscular strength of the pelvic limb. |
| + | |
| + | ==Determining the Site of Spinal Lesions== |
| + | |
| + | * 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. |
| + | * The spinal reflexes used in small animals to assess specific segments are not very useful in adult horses. |
| + | ** However, withdrawal reflexes are useful in recumbent horses with severe lesions. |
| + | *** A stimulus is applied to the distal limb and the reflex results in limb withdrawal. |
| + | |
| + | ===Cervical Lesions=== |
| + | |
| + | * Cervical lesions occur from C1 to C5 |
| + | ** C6 and C7 may also be included. |
| + | * Horses with defects in all four legs are most likely to have a cervical lesion. |
| + | * The pelvic limbs tend to be more severely affected than the thoracic limbs. |
| + | ** This is due to the topographical arrangement of the white matter tracts in the spinal cord. |
| + | |
| + | ====Effects on Reflexes==== |
| + | |
| + | * Cervicofacial reflex |
| + | ** The cervicofacial reflex is tested by lightly stimulating the skin of the lateral neck. |
| + | *** In an intact reflex movement of the lips should be observed. |
| + | *** This reflex varies widely between individual horses. |
| + | *** This is not intact in cervical lesions. |
| + | * Withdrawal reflexes |
| + | ** Only of use in recumbent horses. |
| + | ** In cervical lesions, reflexes in both thoracic and pelvic limbs may be exaggerated. |
| + | *** This is due to a loss of upper motor neuron inhibition. |
| + | |
| + | ===Brachial Lesions=== |
| + | |
| + | * Brachial lesions occur from C6 to T2. |
| + | * Signs of a spinal lesion at this level differ in the thoracic and pelvic limbs. |
| + | ** Thoracic limbs |
| + | *** Lower motor neuron signs |
| + | **** Weakness |
| + | ***** May be mild |
| + | ***** May manifest unwillingness to take the weight on the other thoracic limb when one is picked up. |
| + | **** Muscle atrophy |
| + | *** Withdrawal reflex in recumbent animals may be reduced. |
| + | ** Pelvic limbs |
| + | *** Ataxia |
| + | *** Upper motor neuon weakness |
| + | **** For example, swaying and stumbling. |
| + | *** Withdrawal reflex in recumbent animals may be exaggerated. |
| + | |
| + | ===Thoraco-lumbar Lesions=== |
| + | |
| + | * Thoraco-lumbar lesions occur in the segments T3 to L3 of the spinal cord. |
| + | * In an animal that has pelvic limb ataxia and weakness but no thoracic limb involvement, the lesion will be between T2 and L3. |
| + | ** I.e. caudal to the brachial plexus. |
| + | ** The animal should be closely examined for symmetry over the gluteals and pelvic limbs. |
| + | *** If there is symmetry, the lesion is likely to be at this level. |
| + | *** If there is no symmetry, the lesion is likely to be more caudal, and involve the pelvic outflow. |
| + | * Asymmetry may be detected in the cutaneous trunic reflex. |
| + | ** This is tested by lightly stimulating the skin of the lateral thorax. |
| + | * The withdrawal reflex in the pelvic limb may be exaggerated. |
| + | * Flexibility of the thoracolumbar spine may be assessed. |
| + | ** The skin of the longissimus musculature is firmly stimulated, and observed for: |
| + | *** A lordotic movement over the thorax and cranial lumbar region, and |
| + | *** A kyphotic movement over the caudal lumbar region and gluteals. |
| + | |
| + | ===Lumbosacral Lesions=== |
| + | |
| + | * Lumbosacral lesions occur between the segments L4 and S3. |
| + | * Horses with such lesions may: |
| + | ** Exhibit atrophy of one or more muscles of the pelvic region, and so |
| + | ** Be easy to pull over when standing, and |
| + | ** Be unwilling or unable to take weight on the affected side when the other limb is lifted. |
| + | * More caudal lesions may: |
| + | ** Affect the anal and perineal reflexes. |
| + | *** These are tested by lightly stimulating the skin surrounding the anus and observing for a reflex contraction of the anal sphincter. |
| + | ** Cause paresis of the tail. |
| + | * The withdrawal reflex may be reduced or absent in the pelvic limb. |
| + | |
| + | ===Sacral Lesions=== |
| + | |
| + | * Damage to the savral spinal cord can affect bladder function and control of defaecation. |
| + | |
| + | ====Bladder Incontinence==== |
| + | |
| + | * The bladder is reflexely controlled, via higher order neurones in the caudal brainstem and cerebrum, by the: |
| + | ** Pelvic nerve |
| + | *** Parasympathetic fibres leave the spinal cord in the sacral segments and combine to form the pelvic nerve. |
| + | **** These fibres innervate the smooth detrusor muscle of the bladder wall. |
| + | ** Pudendal nerve |
| + | *** The pudendal nerve innervates the striated muscle of the bladder neck. |
| + | * During micturition, the bladder is evacuated as: |
| + | ** The striated muscle is relaxed. |
| + | ** Stimulation of the pelvic nerve causes the detrusor smooth muscle to contract. |
| + | |
| + | ====Faecal Incompetence==== |
| + | |
| + | * Lesions in the sacral region may also be manifest as faecal incompetence. |
| + | ** In horses, problems are usually caused by defects in the lower motor neurons in the pelvic nerve. |
| + | *** Faeces is retained. |