The neurological examination begins at the head and ends at the tail, emphasising the anatomical location of any lesion as the examination proceeds and allowing completion of the examination a lot faster. The examination consists of evaluation of the head and entire body in the stable and finally evaluation of gait and posture while the animal is moving freely in hand.
An evaluation of behaviour, mentation, head posture and movement, as well as cranial nerves, is undertaken to determine if there is evidence of brain or cranial nerve disease (Figure 1). The examiner can complete all the observations, tests and reflexes involving cranial nerve function; the results can be documented and then specific deficits relating to individual nerves can be correlated (Table 1). Bony and muscular asymmetry, localised sweating, focal muscle atrophy, decreased pain perception and localised painful responses should be noted.
For the most part, neurological gait abnormalities involve degrees of paresis (weakness) and ataxia – the degree of each should be evaluated (mild, moderate, severe for paresis, 0 to 4+ for ataxia). Compressive lesions classically result in clinical signs that appear more severe in the pelvic limbs (probably due to the more peripheral location of the spinocerebellar tracts in the spinal cord) and a two grade difference in spinal cord ataxia is possible with a lesion in the cervical spinal cord.
After completing the neurological examination, the clinician should decide where within the nervous system any possible lesions exist. If this is not clear, it often is worthwhile returning to the patient and performing more critical evaluations.
The following sequence for the equine neurological examination is used by the author:
- Behaviour and mentation (forebrain)
- Head posture (CN VIII)
- Nasal septum sensory perception (forebrain, sensory CN V)
- Head muscle mass (temporalis, masseter, pterygoid) (motor CN V)
- Tongue tone (CN XII)
- Eye movement (CN II, IV, V and VIII)
- Symmetry of eye position with head elevation (CN VIII)
- Menace response (“vision”: CN II, visual cortex, CN VII and cerebellum)
- Pupillary light reflex and swinging light test (CN II
and parasympathetic III) - Palpebral response (CN V and VII)
- Thoracolaryngeal (slap test) (CN X and recurrent laryngeal nerves)
- Local cervical reflex and cervicofacial reflex (at least cervical dorsal and ventral spinal roots and CN VII)
- Cutaneous trunci reflex (dorsal roots, cranial thoracic spinal cord to T8, lateral thoracic nerve)
- Anal sensation and reflex, tail tone (caudal equina)
- Tail pull (upper motor neuron function)
- Gait in straight lines, circling, zig zagging, walking down slopes with head elevated (upper and lower motor neurons, general proprioception, cerebellum, vestibular system)
| Cranial Nerve | Major Function | Reflex and Response Assessment |
|---|---|---|
| I – Olfactory | Sense of smell | – |
| II – Optic | Afferent pathway for vision and light | Menace response, pupillary light reflex, swinging light test |
| III – Oculomotor | Pupillary constriction Extraocular muscles (other) | Pupillary light reflex Medial movement of globe |
| IV – Trochlear | Extraocular muscle (dorsal oblique) | Ventrolateral rotation of globe |
| V- Trigeminal | Sensory to side of head and face Motor to muscles of mastication | Ear, eyelid and lip (facial) reflexes, pain perception from head septum Chewing, jaw tone, muscle mass (temporalis, masseter, pterygoid) |
| VI – Abducens | Extraocular muscle (retractor oculi) Extraocular muscle (lateral rectus) | Eyeball retraction (corneal reflex) Lateral movement of globe |
| VII – Facial | Motor to muscles of facial expression | Ear, eyelid and lip (facial) tone reflexes and movement, facial symmetry |
| VIII – Vestibulocochlear | Afferent branch of vestibular system Sense of hearing | Head posture, induced eyeball movement, normal vestibular nystagmus, normal gait, blindfold test Response to noise |
| IX – Glossopharyngeal X – Vagus XI – Accessory | Sensory and motor to pharynx and larynx | Swallowing (palpation), gag reflex (nasal tube), endoscopy, slap test (vagal and recurrent laryngeal nerves) |
| XII – Hypoglossal | Motor to tongue | Tongue size and symmetry |
At the end of the neurological examination, the clinician should then be able to determine which area of the nervous system is affected:
- Cerebrum
- Brain stem
- Cerebellum
- Peripheral cranial nerves
- Spinal cord
- Peripheral spinal nerves
- Muscles
Many times, the clinician will be able to define even more precisely the exact location of a lesion, or lesions, within these divisions. With the anatomical location of any lesions more or less clearly determined, and following further review of the history of the case, appropriate specific diseases that might occur at such a site can be considered.
