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Performing a meaningful neurological exam

Practical advice from a specialist on performing an equine neurological examination – from head to tail

10 September 2018, at 8:30am

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.

FIGURE 1 Key aspects of an equine neurological examination
FIGURE 1 Key aspects of an equine neurological examination

© Mayhew’s Large Animal Neurology

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)
TABLE 1 Cranial nerve reflex and response assessment
TABLE 1 Cranial nerve reflex and response assessment

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.

Veterinary Advisor at Virbac

Caroline Hahn, DVM, MSc, PhD, DipECEIM, DipECVN, MRCVS, is a board-certified neurologist with a special interest in equine cases. After qualifying from the University of Florida, Caroline completed an internship in equine neurology and orthopaedics, and a residency and PhD in equine neurology.

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