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Neuro Exam for Small and Large Animal Patients: For Vet Techs

by Cathy Barnette - February 18, 2020 at 9:00 AM
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While there are fundamental principles that hold true across all neurologic exams, there are also significant differences in how these examinations are executed, depending on the patient.

Understanding the basics of neurologic examinations in both small and large animals will improve your ability to assist with these examinations and/or perform them independently.

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Mental Status Evaluation 

Before beginning a neurologic exam, it's important to stand back and observe the patient’s behavior. In a small animal patient, this may mean allowing the pet to explore the exam room unrestrained. In a horse or other large animal species, this typically means observing the patient in a stall or in its pasture. 

Talk to the owner about any behavioral changes or other mental changes that have been observed. Look for evidence of depression (quiet, but with appropriate environmental responses), dementia (mentally dull, with inappropriate environmental responses), stupor (lethargic, with minimal response to anything except pain), or coma (lack of response to any environmental stimuli). Look for other abnormalities, such as head pressing, circling, seizures, or hyperesthesia. All of these items are best evaluated from a distance, before disturbing the patient. 

Cranial Nerves

In both small and large animal patients, evaluation of the cranial nerves is typically the next step of a thorough neurologic evaluation. Abnormalities in the cranial nerve examination can help localize whether in the nerves or brain a lesion may be present. 

Common tests performed to evaluate the cranial nerves include the following: 

  • Olfaction: In this test, a desirable food is placed near the patient to see if the patient can locate it based on smell. This test evaluates the function of cranial nerve (CN) 1, the olfactory nerve. 
  • Menace: Move a hand towards the eye, being cautious not to touch the eyelashes. If the patient sees the approaching eye, it should blink protectively. This test evaluates CN 2, the optic nerve, and CN 7, the facial nerve. 
  • Vision: Drop a cotton ball or other object in the patient's field of vision to see whether the patient’s eyes follow the object. This test evaluates CN 2, the optic nerve. 
  • Check the eyes for abnormalities in pupil size, the presence of strabismus (abnormal deviation of the eyes, caused by an abnormality of the extraocular muscles), enophthalmos (a sunken appearance to the eye), or spontaneous nystagmus (abnormal eye movements). Abnormal eye position may be associated with lesions affecting CN 2 (optic nerve), CN 3 (oculomotor nerve), CN 4 (trochlear nerve), CN 6 (abducens nerve), and/or CN 8 (vestibular nerve).
  • Pupillary light reflex: Shine a bright light in the patient’s eye and assess for pupillary constriction. Both pupils should constrict, even when light is only signed into a single eye. This test assesses CN 2 (optic nerve) and CN 3 (oculomotor nerve). (Note: pupillary light reflexes are often slower in horses than in small animal patients.1) 
  • Corneal reflex: While holding the eyelids open, touch the cornea gently. The globe should retract. This reflex assesses CN 5 (trigeminal nerve) and CN 6 (abducens nerve). 
  • Palpebral reflex: Touch the lateral or medial canthus of the eyelids and ensure that the animal blinks. In horses, this reflex should be so strong that the snapping of the eyelids is audible.1 This test assesses CN 5 (trigeminal nerve) and CN 7 (facial nerve). 
  • Intranasal sensation: Insert a hemostat gently into the tip of the nostril and see whether the animal moves away from the stimulus. This test assesses CN 5 (trigeminal nerve). 
  • Assess jaw tone. Loss of jaw tone is typically associated with a lesion of CN 5 (trigeminal nerve), while increased jaw tone is often caused by a myopathy. 
  • Clap loudly and look for a response. The ability to hear is dependent on CN 8 (vestibulocochlear nerve). 
  • Swallowing: In small animals, swallowing is tested by rubbing the patient’s throat to elicit a swallow. In horses and other large animals, the patient is observed while eating. Swallowing is dependent on CN 9 (glossopharyngeal nerve) and CN 10 (vagus nerve). 
  • Assess for the presence of trapezius or brachiocephalicus muscle atrophy. Although rare, these findings can indicate a lesion affecting CN 11 (spinal accessory nerve).
  • Look for atrophy or weakness of the tongue. This can indicate a lesion affecting CN 12 (hypoglossal nerve). 

Gait and Postural Examination 

Patients should be observed at rest and in motion, looking for gait abnormalities. In dogs and horses, an assistant is often used to walk the patient, jog the patient, and lead the patient through a series of turns. Horses are often led across obstacles and over uneven terrain, in order to allow better visualization of subtle abnormalities. In cats and other large animal species, observation is typically performed while allowing the patient to roam freely. 

In small animals, conscious proprioception is used to detect subtle neurologic disease affecting a particular limb. The animal is supported under the chest and each paw is flipped over, so that the dorsal surface of the paw contacts the ground. The animal should correct the paw position (flip the paw) within a few seconds. Other tests that may be used to evaluate gait and postural reactions include hemiwalking (lifting the limbs on one side, forcing the patient to walk on the limbs of the other side), wheelbarrowing (lifting the hindlimbs, forcing the animal to walk on its front limbs), and hopping (lifting three limbs while supporting and moving the patient, to determine whether the patient correctly “hops” on the down limb).

Conscious proprioception and other postural tests are not typically performed in large animals. Some large animal veterinarians may perform a hopping test; other veterinarians, however, feel that the test is too impractical and dangerous to be used routinely.1 If performed, the hopping test in a horse involves lifting one forelimb and forcing the horse to hop on the other forelimb. 

Limb Reflexes and Pain Perception

In small animal patients, tendon reflexes are a valuable component of the neurologic exam. When assessing reflexes, a reflex hammer is typically used to tap a finger that is carefully placed over the tendon of interest. In the forelimbs, biceps, triceps, and extensor carpi radialis tendon reflexes are typically assessed. In the hindlimbs, the patellar, gastrocnemius, cranial tibial, and sciatic reflexes are assessed. Noting the intensity of these reflexes (normal, increased, or decreased) can provide valuable information about the location of spinal cord lesions. 

The withdrawal reflex and deep pain perception are also used to assess small animal patients. It is important to understand the difference between these two tests. Withdrawal means that the patient pulls the limb away when the toe is pinched. This is a reflex, meaning that it can occur without the patient’s awareness. Deep pain perception, in contrast, involves applying a painful stimulus to the animal’s paw and looking for the pet to show a conscious awareness of the pain (looking towards the affected paw, turning to bite, etc). The loss of deep pain, even with an intact withdrawal reflex, indicates a severe spinal cord lesion with a guarded prognosis. 

Limb reflex testing may be assessed in cattle,2 but is not typically performed in horses (with the exception of the withdrawal reflex in recumbent horses).1 

The panniculus response, or cutaneous trunci response, can be used to assess all species. In this test, the dorsal skin of the trunk is pinched and a twitch of the cutaneous muscle can be observed. Spinal lesions are often associated with a dulling of the panniculus response caudal to the site of the injury, while nerve root lesions may cause a dulling of the response only at the site of the lesion. 

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References

  1. Johnson, AL. 2010. How to Perform a Complete Neurologic Examination in the Field and Identify Abnormalities. AAEP Proceedings. 56:331-337. Retrieved from https://aaep.org/sites/default/files/issues/proceedings-10proceedings-z9100110000331.pdf
  2. DVM360. 2008. Bovine neurology: Lesion localization, neurologic exam, and why we care. Retrieved from https://www.dvm360.com/view/bovine-neurology-lesion-localization-neurologic-exam-and-why-we-care-proceedings
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About Cathy Barnette

Cathy Barnette is a practicing small animal veterinarian, freelance writer, and contributor to XPrep Learning Solutions. She is passionate about both veterinary medicine and education, working to provide helpful information to veterinary teams and the general public. In her free time, she enjoys spending time in nature with her family and leading a Girl Scout troop.

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