BACK TO BASICS: FOUNDATIONAL CLINICAL SKILLS FOR EQUINE PRACTICE


unilateral weakness, the tongue curls toward the unaffected side. Grasp the tongue from one side after inserting the hand through the interdental space. Note resistance of the tongue to being stretched and look for atrophy and muscular fasciculations (CN XII). Gently pinch the side of the tongue with a hemo- stat and look for reflex retraction (CN V). Pull the tongue out one side of the mouth, release it, and look for retraction of the tongue back into the mouth. In normal horses, one or two chewing movements occur as the tongue is quickly retracted. Delayed or absent retraction of the tongue back into the mouth can occur with hypoglossal nerve (CN XII) dysfunction, neuromuscular weakness (especially botulism), or obtundation fromcerebral disease.


4. General Examination of the Neck, Trunk, and Limbs


Examination With the horse standing squarely, assessmusclemass, paying particular attention to asymmetries. Note any circumscribed or asymmetric areas of sweating. Firmly press the cranial edge of each of the cervical transverse processes from C3 toC6 on each sidetotest for a pain response. Put pressure on the C6 and C7 interverte- bral joints by pushing medial to the deep pectoral mus- cle infront ofthe shoulder oneachside. Test lateral neck flexion by enticing thehorsetomoveits headto- ward feed held at the point of the elbow, and then the point of the hip.Neck pain revealed by palpation or re- luctance to turn laterally may follow any neck trauma but usually reflects arthritis of intervertebral joints. Press down firmly on each section of the thoracic and lumbar epaxialmuscles to evaluate for back pain. Severe or rapidly developing muscle atrophy indi-


cates denervation and is a localizing sign. Neurogenic muscle atrophy is caused by damage to the lower motor neuron in the ventral column of the gray mat- ter, nerve roots, or peripheral nerves supplying that muscle. Neurogenic atrophy of thoracic limbmuscula- ture results from lesions of the C6 to T2 spinal cord segments or roots, brachial plexus, or peripheral nerves, while atrophy of pelvic limb muscles reflects involvement of L3 to S2. Anesthesia of a strip of skin is caused by loss of the segmental sensory nerve, dor- sal nerve root, or connections in the spinal cord. Because sympathetic fibers are distributed with spi- nal nerves, spontaneous sweating may occur over de- nervated skin.


Cervicofacial Reflex


Place the left index and middle fingers at the commis- sure of the left lip, and then strike the skin over the bra- chiocephalicus muscle with the closed tip of the hemostat. Begin at the cranial end of the neck and continue back to the shoulder. The expected response is facial contraction, detected as retraction of the commis- sure of the lip, and contraction of the brachiocephalicus and cutaneous colli, observed as shrugging of the shoulder, lateral jerking of the head, and twitching of


the skin of the neck. This reflex typically is reduced at the level of a cervical spinal cord lesion but is normal cranial and caudal to the lesion.


Slap (Thoracolaryngeal) Test


While standing on the left side, reach under the horse’s neck and hook the index and middle fingers of the left hand over the highest palpable point of the larynx—the muscular process of the arytenoid. Have the handler move the head slightly to the left of midline, and then gently strike the horse behind the withers several times with the palm of the right hand. The expected response is slight palpablemovement (adduction) of the arytenoid in response to each slap. Repeat the procedure from the right side. Sensory input to this reflex is the sensory nerves


and roots under the area that is slapped (approxi- mately T7–T11). Central pathways are thought to cross to the other side at this level and pass rostrally to the nucleus ambiguus in the white matter of the spinal cord, and then efferent fibers pass out in the vagus nerve via the recurrent laryngeal nerve to in- nervate the contralateral laryngeal adductor muscles. Severe cervical spinal cord disease often affects this test bilaterally, and the vagus and recurrent laryngeal nervesmay be affected at the guttural pouch orwithin the jugular groove.


Cutaneous Trunci Reflex (Panniculus)


To elicit the panniculus reflex, use the thumb to firmly prod the lateral thoracic wall, beginning crani- ally just behind the shoulder and extending caudally to the last intercostal space. Check every intercostal space both ventrally and dorsally. For safety, firmly grasp the back of the mane with the left hand and face backward when testing the reflex because horses that resent this test will try to kick the examiner. Repeat on both sides of the horse. A normal response is twitching of the skin, with or without indication of conscious perception of the stimulus. The reflex pathway is input from sensory thoracic


nerves to the ipsilateral spinal cord, where it courses rostrally via interneurons to end in the C8 and T1 seg- ments, and thence via the brachial plexus to the lat- eral thoracic nerve and the cutaneous trunci muscle. Interruption of this pathway in the spinal cord white matter results in loss of the reflex from approximately the point of the lesion caudally. A lesion of the sensory nerve will only affect the reflex within the same der- matome (skin strip), while loss of lateral thoracic nerve function ablates the entire ipsilateral reflex. Horses with botulism may display a generalized loss of panniculus reflex bilaterally.


Back Reflexes


Make sure that the pelvic limbs are positioned equally and squarely, and then stroke the closed tip of the hemostat caudally along the skin over the longissimus dorsi muscle, from mid-thorax caudally to the level of the tuber coxae. For safety, hold the back part of the mane with the other hand. The expected response is


AAEP PROCEEDINGS / Vol. 68 / 2022 201


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