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| − | [[Neurological Examination of Horses Overview]] | + | #redirect[[:Category:Neurological Examination - Horse]] |
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| − | [[Neurological Examination Initial Observation - Horse]]
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| − | ==[[Cranial Nerve Examination - Horse]]==
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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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