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| | ==[[Site of Spinal Lesions Determination - Horse]]== | | ==[[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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