Neurologic Examination

There are several additional tests that do not fall into these categories, such as assessment of muscle tone and muscle atrophy, perineal reflex, and cutaneus trunci reflex and evaluation for nociception and neck and/or back pain. As with a general physical examination, the neurologic examination should be conducted the same way every time to develop a routine and prevent errors. Using a neurologic examination form is strongly recommended (see Neurologic Examination Form).

The patient’s mental status should be assessed during history-taking and throughout the appointment. The patient should be alert and responsive at all times. The patient’s interactions with humans and its environment should be noted, including:

• Whether the patient is fully alert and responsive 
• Whether the patient has difficulty navigating corners or tight spaces
• Whether the patient walks in circles
• Whether the patient responds to its name

Analysis of gait and body posture early in the examination is especially important in cats that are nervous or stressed, as they may refuse to walk later if gait is analyzed after the hands-on portion. 

Dogs should be walked on a short leash away from, toward, and in profile to the observer (Figure 1), ideally on a surface with good traction (eg, concrete, grass, nonslip floors). The gait should be observed for signs of weakness (paresis) or paralysis (plegia), ataxia, and lameness. When describing the gait, first identify whether the patient is ambulatory or nonambulatory, then identify which limbs are affected and the degree of weakness (Table). For instance, a dog with nonambulatory paraparesis is too weak to walk on its own but retains voluntary motor function in the pelvic limbs and is normal in the thoracic limbs.

The patient should be evaluated for ataxia (ie, incoordination). There are 3 types of ataxia: proprioceptive, cerebellar, and vestibular. Proprioceptive ataxia is characterized by scuffing or dragging the paws on the ground, knuckling over, crossing over, or interference (ie, limbs hitting each other when walking). Vestibular ataxia is characterized by leaning or falling to one side. Patients with vestibular ataxia often use a wall for support while walking. Cerebellar ataxia is characterized by dysmetria (ie, unequal range and force of each step), often with hypermetria (ie, overflexion of the elbows in the thoracic limbs or hips/stifles in the pelvic limbs). Patients will sometimes have an overreaching, long-strided, floating gait, especially in the thoracic limbs, that can look like cerebellar hypermetria. However, this type of gait is caused by an upper motor neuron (UMN) lesion. The key difference between cerebellar hypermetria is overflexion of the elbow as compared with straight elbows in the overreaching UMN gait. Finally, any postural abnormalities (eg, head tilt, head turn, torticollis) should be noted.

The hands-on examination should take place after gait and mentation are evaluated. Most neurologists start with the cranial nerves (CNs), either by testing the CNs in numerical order or by location (eg, performing all eye-related tests then evaluating nose/face, ears, mouth). There are 12 pairs of CNs, but not all are routinely tested as part of the neurologic examination. 

• Reflex hammer 
• Hemostats
• Strong light source (eg, transilluminator, halogen penlight)
• Lens (direct or indirect)

The menace response (Figure 2) is the first step of the CN examination and tests CNs II and VII. Cover one eye, then bring the hand toward the other eye in a “menacing” gesture. Be careful not to generate wind current or touch any whiskers or eyelashes, as it is important not to let the patient feel the hand’s presence. It may be necessary to lightly tap the animal’s head to get its attention. The animal should blink. Perform the same steps in the other eye.

Test the pupillary light reflex to test cranial nerves II and III. Use a strong, focused light source (eg, transilluminator, halogen penlight).

Perform a fundic examination. The optic disc is the only part of the CNS that can be directly evaluated on clinical neurologic examination. Retinal abnormalities also provide clues to systemic health. Either a direct (ophthalmoscope) or an indirect (lens and transilluminator) fundic examination can be performed, but the authors prefer an indirect examination so that the observer’s face is not immediately next to the patient’s mouth.

Test the palpebral (blink) reflex by lightly tapping the medial and lateral canthus of both eyes to assess the patient’s ability to blink, which tests CNs V and VII. If possible, approach the eyes from behind the head so the patient cannot see the instrument approaching and give a false-positive result. Test corneal sensation (CNs V and VII) and globe retraction (CNs V and VI) by gently touching the cornea with a sterile cotton swab. The normal response includes eyelid closure and eyeball retraction. Corneal sensation and globe retraction are typically tested only when other CN abnormalities are noted, as all 3 of the involved CNs (V, VI, and VII) in these reflexes can be tested by other means; for example, sensation (V) can be tested by stimulating other regions of the face, and facial nerve (VII) function can be tested through menace response and palpebral reflex.

Evaluate for physiologic nystagmus (ie, “doll’s eye”) by turning the animal’s head from side to side and up and down. This should induce a normal nystagmus with a fast phase in the direction of head movement. Determine whether the patient has abnormal (pathologic) nystagmus at rest (ie, neutral body position) and in different body positions (eg, on side or back). Abnormal nystagmus is common with vestibular dysfunction. Pathologic nystagmus should be characterized by the direction of the fast phase and whether it is horizontal, rotary, or vertical. Evaluate CNs III, IV, and VI by looking for strabismus or abnormal eye movements.

Palpate the patient’s head to assess for pain or atrophy of the muscles of mastication. Asymmetric atrophy of the masticatory muscles is suggestive of disease of ipsilateral trigeminal nerve (most often trigeminal nerve sheath tumor), whereas bilateral atrophy with difficulty opening the jaw is most common with masticatory muscle myositis.

Stimulate (via touch or pinch) different areas of the head to assess sensation (CNs V [all over face] and VII [inner surface of pinnae]) and motor response (CN VII).

Using a small blunt instrument, touch the nasal mucosa just inside the nose. The patient should pull its head away. This tests CN V and the contralateral cerebral cortex as the patient interprets the stimulus and pulls its head away.

Open the patient’s mouth and assess the degree of jaw tone (CN V). Evaluate the tongue for deviation, atrophy, or fasciculation (CN XII). For a cooperative dog, perform a gag reflex (CNs IX and X) by gently touching the oropharynx or laryngopharynx. The dog should swallow. Do not perform a gag reflex in aggressive dogs, nervous dogs, or any cat. Instead, lightly palpate the laryngeal region externally to induce swallowing.

Next is evaluation of postural reactions. The authors recommend that several postural reaction tests be performed, as subtle abnormalities may not be detected on general proprioception, which typically includes paw replacement, “knuckling,” and conscious proprioception).

Measure general proprioception (Figure 3) in all limbs. Support the patient’s trunk (for the thoracic limbs) and below the abdomen (for the pelvic limbs) so that it is minimally weight-bearing on the limb but maintains good contact with the ground.

One at a time, turn each paw over so that the dorsum of the paw is on the ground. The patient should immediately return the paw to a normal position. Watch for delays in replacement or abnormal placement.

Perform at least one additional test to assess proprioception, as some patients will have normal general proprioception but will show abnormalities on the other tests. Do not rely solely on general proprioception, as failure to return the paw to normal position can result from use of a muzzle or the owner distracting the dog through petting. These additional tests include hopping (ie, lifting the patient off the ground to hop on one leg laterally), wheel-barrowing (ie, lifting the pelvic limbs off the ground and pushing the patient forward on its thoracic limbs), and extensor postural thrust (ie, lifting the patient off the ground and bringing the pelvic limbs to the ground with the patient walking backward). The normal reaction is a swift, normal placement of the limb(s) in the direction of movement. Visual and tactile placing can be performed in cats and small dogs. In cats, it is often easier to perform these proprioceptive tests than it is to perform general proprioception, although some cats refuse to cooperate.

Ideally, reflexes should be tested in lateral recumbency, but they can also be tested in standing (uncooperative) patients. The most reliable reflexes are the patellar and withdrawal (flexor) reflexes. Other reflexes (eg, cranial tibial, extensor carpi radialis) are less reliable and commonly produce false-negative results. The patellar reflex (Figure 4) can be used to evaluate the femoral nerve.

To perform the patellar reflex, hold the pelvic limb up, with the knee slightly flexed, and strike the straight patellar tendon with a reflex hammer. The patient should extend the stifle.

Pinch the webbing between the toes. A complete withdrawal reflex (Figure 5) involves fully flexing all joints in the limb. If the patient does not respond, use hemostats with the least amount of pressure necessary to induce flexion. The withdrawal reflex tests a combination of nerves (ie, median, ulnar, musculocutaneous, axillary, radial) in the thoracic limbs and the sciatic nerve in the pelvic limbs, although the femoral nerve is involved in hip flexion.

Of note, limb withdrawal is a local spinal reflex and not a sign of intact pain perception, which requires a conscious response (eg, crying, whining, attempting to bite).

Additional tests include evaluation of muscle tone and atrophy, cutaneus trunci reflex, perineal reflex or anal tone, nociception, and neck or back pain. Muscle tone and atrophy of the trunk and limbs are most often tested with the patient standing in a normal position but can also be evaluated with the patient in lateral recumbency.

To test the cutaneus trunci reflex, lightly pinch the skin with hemostats on either side of midline starting at L6 and moving cranially. The skin should flinch bilaterally as the cutaneus trunci muscle is stimulated. Once a normal response is elicited, there is no need to continue further cranially. Cutaneous sensory fibers enter the spinal cord via segmental spinal nerves, and some cross over immediately in the spinal cord and ascend bilaterally to synapse on cell bodies, giving rise to the lateral thoracic nerve (C8-T1). Because sensory fibers ascend the spinal cord bilaterally, a skin twitch should occur on both sides, regardless of the side pinched. Animals with a spinal cord lesion may have an absent cutaneus trunci reflex (ie, cut-off) that occurs approximately 2 to 3 segments (range, 0-4) caudal to the spinal cord lesion.¹ Patients with lateral thoracic nerve dysfunction (eg, brachial plexus injury, nerve sheath tumor) may have an absent cutaneus trunci reflex ipsilateral to the lesion, regardless of which side is pinched. 

Near the end of the examination, a hemostat can be used to lightly stimulate the perianal area. The external anal sphincter should constrict reflexively. Digital rectal examination may be required to further evaluate anal tone.

Testing for back or neck pain and nociception (ie, conscious perception of a noxious stimulus) should be conducted at the end of the examination so that it does not alter the results of the rest of the neurologic examination. 

Palpate firmly down the length of the vertebral column, then test for range of motion of the neck and response to elevation of the tail. Nociception should only be tested in affected limbs that are paralyzed. Although there are exceptions, if a patient can voluntarily move the limb at all, nociception in that limb should be intact. Nociception should be evaluated in the affected limb(s) by pinching the digits (lateral and medial toes) with a hemostat. Nociception should also be tested in the tail. The patient should have a visible response to the stimulus, such as turning around to look, crying, whining, biting, or experiencing a change in respiratory rate to indicate perception of the noxious stimulus. As stated above, flexion of the limb is a local reflex and not a sign of conscious perception.

Clinical neurologic signs depend on lesion location rather than etiology. Thus, the goal of the neurologic examination is to determine the affected area of the nervous system first and, from there, formulate a list of possible differentials. After this, a diagnostic and therapeutic plan can be developed.