A thorough neurologic examination can be performed in 10 to 15 min. The main components are evaluation of mental status and behavior, gait and postural reactions, cranial nerves, spinal reflexes, palpation, and pain perception. General observation of mental status, posture, attitude, and gait is performed while taking the history. Once the history is clarified, the remainder of the examination is completed. Based on the presenting complaint, it may be necessary to modify portions of the examination. For example, a tetraplegic patient after being hit by a car is not subjected to postural reactions for fear of exacerbating a possible unstable cervical injury. Start with procedures least likely to upset the patient. Disagreeable or painful procedures, such as palpating painful areas, are left until the end of the examination. If the clinician upsets the patient early on, it may be difficult to complete the examination. Also, once pain is elicited, the patient will often anticipate further painful stimuli, making it difficult to determine if other procedures are truly painful. The purposes of the various procedures are explained to the client as the examination proceeds. This lessens the client’s distress when he or she observes unfamiliar procedures performed on a pet. Some abnormalities will be blatantly obvious, whereas others will be subtle. A subtle abnormality is still an abnormality. There is a tendency for subtle abnormalities to be chalked up to anything but a neurologic lesion; trust your neurologic findings.
A pleximeter (rubber hammer) is used to test myotatic reflexes. Other instruments, such as scissors, are not recommended because these do not provide a consistent stimulus and appear less professional to the client. A hemostat is often useful when testing for nociception (deep pain perception) or eliciting a cutaneous trunci reflex. A strong light source is necessary to elicit pupillary light reflexes in excited dogs and cats. A cotton-tipped applicator or a piece of cotton to cover a hemostat is useful to evaluate the nasal sensation. Finally, a moistened cotton-tipped applicator stick is recommended for performing the corneal reflex. A light touch with your fingertip is acceptable, but if a client is watching you, it may appear that you are poking the pet in the eye.
Before handling the patient, let the patient have the run of the examination room, if ambulatory, and observe the patient’s reaction to the surroundings.
Mental status should be evaluated in terms of both level and content of consciousness.
Level of consciousness
Alert—the patient responds appropriately to environmental stimuli.
Depressed/obtunded—the animal is drowsy but arousable. Depressed/obtunded dogs and cats are typically inattentive and display little spontaneous activity.
Stuporous—the patient is in a sleep state, but arousable with a strong stimulus.
Comatose—the patient is unconscious and cannot be aroused even with painful stimuli.
Content of consciousness
Refers to the quality of consciousness
Dementia/delirium—the patient has an alert level of consciousness, but exhibits abnormal behavior and responds inappropriately to stimuli.
Mental status is a function of the ascending reticular activating system (ARAS) that extends over the entire length of the brain stem to activate the cortex. Brain-stem disease can cause changes in mental status.
Abnormal behavior is identified by comparing the patient’s behavior to expected behavior for animals of a similar breed and age. The client is often able to bring subtle changes in behavior to the veterinarian’s attention. Behavioral changes may be an indication of forebrain (cortical) disease.
Attitude/posture
Attitude refers to the position of the eyes and head in relation to the body. Abnormal head position is often manifested as a head tilt or a head turn (Fig. 2.1). In a patient with a head tilt, one ear is held lower than the other. It is also important to make sure that the eye in the affect side is also lower than the other, because sometimes ear diseases can cause a dropped ear without an associated head tilt. Unilateral vestibular dysfunction will often cause a head tilt. When an animal develops a head turn, the head is held level, but the nose is turned right or left. Animals with forebrain lesions may tend to turn their heads and circle in one direction. (Videos 7 and 8).
Figure 2.1 A head tilt posture should be differentiated from head turn. Head tilt indicates vestibular disease, whereas head turn suggests a forebrain (thalamocortical) lesion. (The Ohio State University. Reproduced with permission.)
Posture is the position of the body with respect to gravity. Abnormal postures, such as a wide-based stance, are common in dogs and cats with neurologic disease. Several classic abnormal postures indicative of neurologic dysfunction have been described.
Decerebrate rigidity—due to a brain-stem lesion and characterized by extension of all limbs and sometimes opisthotonus (dorsiflexion of the head and neck). A decreased level of consciousness (often stupor or coma) usually accompanies this posture.
Decerebellate rigidity—due to an acute cerebellar lesion and characterized by opisthotonus, thoracic limb extension, and flexion of the hips. Consciousness is not impaired due to lack of brain-stem involvement.
Schiff–Sherrington posture—frequently encountered in veterinary practice and caused by a lesion in the thoracic or lumbar spinal cord segments. Extension of the thoracic limbs (best appreciated in lateral recumbency) with paralysis of the pelvic limbs characterizes Schiff–Sherrington posture (Fig. 2.2).
Figure 2.2 Schiff–Sherrington posture in a Dachshund with thoracolumbar intervertebral extrusion.
Kyphosis, lordosis and scoliosis—abnormal spinal postures frequently observed. A kyphotic posture is commonly seen with painful conditions of the thoracolumbar vertebral column. Scoliosis may be seen with congenital malformation and in cases of caudal occipital malformation (Chiari-like syndrome and syringomyelia). Lordosis is infrequently seen and reflects weakness of the epaxial musculature.
Abnormal limb postures—plantigrade or palmigrade postures are used to describe an abnormal posture of the pelvic or thoracic limb, respectively (Fig. 2.3). These postures are frequently seen in cases of neuromuscular diseases, primarily polyneuropathies, but can also be seen in patients with musculoskeletal diseases.
Figure 2.3 (A) Palmigrade posture in a cat. (B) Plantigrade posture in a dog.
Gait (Video 2)
Lameness
Limb pain can cause a limp when the patient tries to bear weight on a painful limb and then quickly plants the contralateral limb to relieve the pain. As a result, the stride of the painful limb is often shortened. When a single limb is severely painful, it is often carried. This is in contrast to a paretic limb, which is often dragged. Lameness is usually caused by orthopedic disease, but some neurologic lesions—such as attenuation or inflammation of a nerve root or spinal nerve by intervertebral disc extrusion or nerve sheath tumor—can cause lameness. This form of lameness is often referred to as a “root signature.”
Patients with bilateral limb pain, such as hip disease or ruptured cruciate ligaments, may not walk at all or have short-strided, stilted gaits. This can mimic weakness due to neurologic disease.
Lower motor neuron (LMN) weakness can cause a short-strided gait in the affected limb(s).
Ataxia—inability to perform normal, coordinated motor activity that is not caused by weakness, musculoskeletal problems, or abnormal movements, such as tremor. There are three types:
Sensory or proprioceptive ataxia (Videos 11, 26 and 27)
Loss of the sense of limb and body position due to interruption of ascending proprioceptive pathways (primarily unconscious proprioception).
Characterized by clumsiness and incoordination, resulting in a wide-based stance and a swaying gait. This type of ataxia is often seen in association with paresis. The stride of the affected limb(s) is often longer than normal and the toes may drag or scuff the ground.
Caused by a lesion affecting primarily the white matter of the spinal cord (unconscious proprioceptive pathways).
Cerebellar ataxia (Videos 9 and 21)
Inability to regulate the rate and range of movement (unconscious proprioception).
Characterized by dysmetria, especially hyper-metria—an overreaching, high-stepping gait.
Caused by cerebellar disease or selective dysfunction of spinocerebellar tracts (less likely).
Vestibular ataxia (Videos 8, 19 and 20)
Unilateral vestibular lesions cause leaning and falling to one side. Other signs of vestibular disease, such as head tilt and abnormal nystagmus, may be evident.
With bilateral vestibular dysfunction, the patient maintains a crouched position, is reluctant to move, and exhibits side-to-side head movements, without an obvious head tilt (since both vestibular receptors and nuclei are affected).
Paresis/paralysis
Paresis is a partial loss of voluntary movement. This is manifested as a decreased rate or range of motion, increased fatigability, decreased muscle tone, or limited ability to perform certain motor acts. Paralysis (plegia) is a complete loss of voluntary movement. Paresis or paralysis indicates a lesion of either the upper motor neuron (UMN) system or the lower motor neuron (LMN) system. It is not possible to discriminate between UMN weakness and LMN weakness based solely on the severity of the weakness.
Abnormal movements
Tremor—a rhythmical, oscillatory movement localized to one region of the body or generalized to involve the entire body. A terminal tremor, or intention tremor, occurs as the body part nears a target during goal-oriented movement. This is most evident as a head tremor when the patient attempts to sniff an object, eat, or drink. A postural tremor occurs as the limb or head is maintained against gravity.
Myotonia—delayed relaxation of muscle following voluntary contraction. Myotonia is manifested as muscle stiffness that is relieved by exercise. Attacks of myotonia may culminate in recumbency with rigid extension of the limbs. Some patients with myotonia will display “dimpling” of sustained indentation of affected muscle when percussed.
Myoclonus—a brief, shock-like muscle contraction producing a quick, jerking movement of a body part.
Postural reactions (Video 3)
Postural reactions test the same neurologic pathways involved in gait, namely the proprioceptive and motor systems. Their main value is detecting subtle deficits or inconspicuous asymmetry that may not be obvious during the observation of gait. Postural reactions are also useful in discriminating between orthopedic and neurologic disorders. Frequently it is only necessary to perform two postural reaction tests: proprioceptive positioning and hopping.
Proprioceptive positioning
Support the animal to avoid body tilt and turn one paw over so that the dorsal surface is in contact with the ground. The patient should immediately return the foot to a normal position (Fig. 2.4).
Figure 2.4 Proprioceptive positioning is evaluated with the patient supported in a standing position in the pelvic (A) and thoracic limbs (B). Proper support of the patient is essential. The dorsal surface of the paw is placed on the floor without pushing it down. The patient should immediately replace the paw to a normal position.
When properly supported, most patients with orthopedic disease will have normal proprioceptive positioning. On the other hand, proprioceptive pathways are often compromised early in the course of neurologic diseases, so defects in proprioceptive positioning may be detected before there are obvious signs of weakness.
Hopping
Hold the patient so that the patient’s weight is supported by one limb and move the animal laterally. The amount of support and the technique are different in small dogs or cats (Fig. 2.5 A and B), compared to large dogs (Fig. 2.6 A and B). Normal animals will hop on the limb while keeping the foot under their body for support.
Figure 2.5 The hopping response in small dogs and cats is tested by lifting and supporting the patient such that most of its weight is borne on one limb. The patient is moved laterally to test the thoracic limb (A) and pelvic limb (B). Note how the support and position of the hands differ.
Figure 2.6 The hopping response in large dogs can be tested by just lifting the contralateral limb and moving the patient laterally to test the thoracic limb (A) and pelvic limb (B). It is unnecessary to try to hop medially or cranially.
Each limb is tested individually and responses on the left and right are compared. This is a sensitive test for subtle weakness or asymmetry.
Placing response
The nonvisual (tactile) test is performed first. Cover the patient’s eyes, pick the animal up, and move it toward the edge of a table. When the paw touches the table, the animal should immediately place the limb forward to rest the paw on the table surface (Fig. 2.7).
Figure 2.7 Tactile placing is tested by covering the patient’s eyes and moving the patient toward the edge of a table. The test can be brought toward the table frontally (A), or laterally (B). Normal dogs and cats will place their paw on the table as soon as they contact the edge of the table.
Visual placing is tested similarly, except the patient’s eyes are not covered. The normal response is to place the paws on the surface as the table is approached, before the paws make contact with the table. This test may detect visual deficiencies.
Hemiwalking, wheelbarrowing, and extensor postural thrust
These tests can be performed if other postural reactions are equivocal.
For hemiwalking, hold up the limbs on one side of the body and move the patient laterally (similarly to the technique demonstrated in Fig. 2.6). The normal reaction is as described for the hopping response.
Wheelbarrowing in the thoracic limbs is done by supporting the patient under the abdomen so that the pelvic limbs do not touch the ground and moving the patient forward (Fig. 2.8). Normal animals will walk with symmetrical, alternate movements of the thoracic limbs.
Figure 2.8 Wheelbarrowing is tested by supporting the patient under the abdomen so that the pelvic limbs do not touch the ground and moving the patient forward.
Extensor postural thrust is tested by lifting the patient by the thorax and lowering the pelvic limbs to reach the floor. Normal patients will move the pelvic limbs caudally as soon as they touch the floor (Fig. 2.9).
Figure 2.9 Extensor postural thrust is tested by supporting the patient under the thorax and lowering it until it touches the ground.
Figure 2.10 Ventral aspect of the canine brain, showing the relative anatomic positions of the cranial nerves. (The Ohio State University. Reproduced with permission.)
Somatic motor to most of the extraocular muscles (dorsal, medial, ventral rectus; ventral oblique; levator palpebrae superioris) Parasympathetic innervation to pupil (pupillary light response)
CN IV
Somatic motor to dorsal oblique muscle of the eye
CN V
Somatic motor to muscles of mastication Somatic motor to tensor tympani muscle Sensory to most of face
CN VI
Somatic motor to lateral rectus and retractor bulbi muscles (extraocular)
CN VII
Somatic motor to muscles of facial expression Somatic motor to stapedius muscle Parasympathetic innervation to salivary glands (mandibular, sublingual)a and lacrimal, palatine, and nasal glandsb Sensory to inner pinna Sensory (mechanoreception, thermal) and taste to rostral 2/3 of tongue (chorda tympani nerve)c
CN VIII
Vestibular function and hearing
CN IX–XI
Parasympathetic innervation of viscera (CN X) Parasympathetic innervation to salivary glands (parotid and zygomatic, CN IX)d Sensory and taste to caudal 1/3 of tongue (CN IX) Sensory innervation of pharynx (CN IX and X) Somatic motor for laryngeal and pharyngeal function (nucleus ambiguus)
CN XII
Somatic motor to extrinsic and intrinsic tongue muscles
a Postganglionic axon in CN V, mandibular branch (after mandibular and sublingual ganglia).
b Postganglionic axon in CN V, maxillary branch (after pterygopalatine ganglion).
c Chorda tympani nerve joins lingual branch of mandibular branch of CN V near middle ear.
d Postganglionic axon in CN V, mandibular branch (after otic ganglion).
CN I (olfactory nerve) is not routinely tested. After ascertaining patency of the nostrils, cover the patient’s eyes and present a morsel of food beneath the nose, observing for normal sniffing behavior. Irritating substances, such as ammonia or isopropyl alcohol, should not be used, because they stimulate trigeminal nerve endings in the nasal passages and produce false results.
CN II (optic nerve)
Note pupillary size and any anisocoria before actually testing the pupillary light reflex (Fig. 2.11). There should be a direct and consensual pupillary light reflex in each eye (Fig. 2.12).
Figure 2.11 The size and pupillary symmetry are tested by holding a good light source one to two feet away from the patient’s face so that the light shines equally on both eyes.
