How to perform a neurologic exam in the horse

Introduction

The neurologic examination in the horse must include the evaluation of behavior, state of consciousness, cranial nerves, posture, and postural reactions, segmental (spinal) reflexes, palpation, gait evaluation, and nociception in recumbent horses with no obvious voluntary movement. Do not forget the autonomic nervous system which includes the sympathetic, parasympathetic, and intrinsic enteric plexuses. Most of the neurologic exam is based on observation. Key points include safety first, observation, know what is normal, and tailor the exam to the individual (safety, domestication, cooperation, severity of deficits). A comprehensive examination will aid in the localization of disease. A complete history including vaccination status and determination of the overall health of the horse are essential to obtain.

Precaution must be practiced when dealing with a horse with acute rapidly progressive onset of disease and rabies must be a consideration, particularly in endemic areas. Furthermore, highly contagious diseases such as herpes-1 myeloencephalopathy must be considered in horses with fever.

Neurologic examination

The goals of the neurologic examination are to determine: 1) If the horse is normal or abnormal, 2) neuroanatomical localization, 3) list most likely causes of disease. To determine the most likely causes of disease, the following essential information is required: 1) Neuroanatomical localization, 2) signalment, 3) onset (rapid versus insidious), 4) duration (acute, subacute, chronic), 5) progression (+/-), 6) fever (+/-), 7) pain (+/-), and 8) one animal versus multiple in the same facility. The examination consists of evaluating the neurologic status while the horse is at rest (static) and during movement (dynamic).

Examination at rest:

1. Behavior and mentation
2. Cranial nerves
3. Posture (head, neck, trunk, limbs, tail)
4. Postural reactions (i.e., proprioceptive positioning)
5. Segmental (spinal) reflexes
6. Palpation

Examination during movement:

1. Gait evaluation + head, neck, trunk, limbs and tail posture while moving
2. Nociception (pain perception only in non-ambulatory animals with no obvious voluntary movement)

Behavior. Normal: Bright, alert, responsive. Abnormal: Any compulsive behavior (e.g. walking, playing with water, chewing), barking, star gazing, looking at his flanks.

Mentation/state of consciousness. Normal: Bright, alert, responsive. Abnormal: 1) Obtundation, 2) Stupor, 3) Coma. Obtundation: From mild to severe (recumbent) but always responsive to non-painful stimuli (e.g., touch, sound, palpation). Stupor: Recumbent not moving, appearing unconscious, and only responsive while applying painful stimuli (e.g. pinched with forceps, electric probe). Coma: Recumbent not moving, appearing unconscious and not responsive to any kind of stimuli (you might observe reflexive movement, but the animal does not respond consciously to stimuli).

Cranial nerves. These include olfactory (I), optic (II), oculomotor (III), trochlear (IV), trigeminal (V with its 3 branches: maxillary, mandibular, ophthalmic), abducens (VI), facial (VII), vestibulocochlear (VIII), glossopharyngeal (IX), vagus (X), spinal accessory (XI), and hypoglossal (XII). Cranial nerve responses, reactions, and reflexes must be evaluated. Simple observation of the horse while standing and eating, and response to noise can reveal deficiencies. For detailed specific function of each cranial nerve, the reader is referred elsewhere.

Posture and postural reactions. Posture of the head, neck, trunk, tail, and limbs is important. Head tilt, neck turn, whole body leaning, trunk turned, hunched back, wide- or narrow-based stance, tail down or up or pulled to the side could be observed with neurologic disease. Postural reactions (including proprioceptive placing and hopping tests) can be performed with caution. Again, examiner observation is essential to note placement of the limbs.

Segmental (spinal) reflexes. The evaluation of segmental reflexes is limited in the horse, but should be tested whenever possible. Segmental reflexes that can be readily evaluated include cervicofacial/auricular, cutaneous trunci, perianal, and perineal. For appropriate performance and interpretation of other reflexes, the horse must be relaxed (no tone, recumbent and relaxed). Therefore, not tested in standing animals. However, these reflexes are easily tested in neonatal foals when placed in recumbency and performed when relaxed.

Palpation. Palpation of the horse’s body including the head can reveal abnormalities not obvious on visual inspection. Check for symmetry, shape, pain, swelling, temperature, sweating, and masses. Palpate muscles, bones, and joints; do flexion and extension of joints to assess for pain and mobility. Examine the horse carefully for any muscle atrophy. Check tail tone and anal tone. Look for any loss of skin sensation (hypalgesia or analgesia), increased sensitivity (hyperesthesia), or abnormal sweating (sympathetic denervation).

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