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The neurologic examination for the busy small animal veterinarian (Proceedings)
A complete neurologic examination is an essential component of the physical examination for patients with suspected neurologic disorders, but is sometimes not performed because of the time constraints of a busy practice.
A complete neurologic examination is an essential component of the physical examination for patients with suspected neurologic disorders, but is sometimes not performed because of the time constraints of a busy practice. At other times, patients with symptoms of neurologic disease can seem intimidating for those not accustomed to performing the neurologic examination. However, with practice, a basic understanding of neurology and a few tips, the neurologic examination can easily be incorporated into all physical examinations.
Before the neurologic examination
The patient's signalment (age, breed, sex) and history should be obtained before the neurologic examination. The following list of questions is important for all patients in whom neurologic symptoms are present or suspected, but is by no means complete. It is easy to incorporate these questions when obtaining a history, or they may asked in a questionnaire that is filled out by a client prior to examination. For others, having a trusted technician obtain answers to these questions prior to the veterinarian entering the examination room may be possible.
• What is the main concern about your pet?
• Was the onset of symptoms sudden or gradual?
• Have the symptoms progressed, improved, remained the same or do they come and go?
• Has your pet seemed painful?
• Is one part or side of the body affected more than others?
• Has your pet had any seizures? Describe what their body does during the seizure.
• Have these symptoms occurred before?
• What medications does your pet receive? How has this problem been treated?
• Obtain a general medical history, including previous illnesses, appetite, vaccinations, etc.
Components of the neurologic examination
The neurologic examination should cover all areas of the nervous system, including the brain, spinal cord and neuromuscular system. The component parts of the neurologic examination include 1) evaluation of mentation, 2) observation of gait and posture, 3) postural reactions, 4) spinal cord reflexes, 5) cranial nerve examination, 6) palpation of the vertebral column, skull and muscles and 7) sensory testing. In most instances it is preferable to begin with the least threatening components of the examination and work towards those areas of the examination which may be resented most or painful to the patient. Whenever possible, all components of the examination should be covered, however there are situations in which an abbreviated examination is necessary. One such instance is with aggressive patients. Often the patient's response to a stimulus on the neurologic examination is subtle and requires some degree of cooperation from the patient. If a animal does not allow examination with light restraint, increasing physical restraint rarely provides useful information from the neurologic examination. Similarly, accurate neurologic assessment can not be obtained in patients given chemical restraint. The safety of the investigator, pet owner and pet should be taken into consideration when deciding upon the components of the neurologic examination for each individual patient.
Observation of gait and posture
Put the patient on the floor. This seems simple but often pet owners have the patient waiting for the veterinarian on the examination table before the examination begins. If possible, observe the patient while walking on and off leash in a area with good traction. If necessary take the patient outside on a leash. Often weakness or gait changes will be apparent within just a few steps. If deficits are not readily observable, having a patient go up and down stairs, an incline or turning quickly may make more subtle deficits apparent. It is preferable to have an assistant or the pet owner to walk the pet so the veterinarian can observe the gait more accurately.
When observing a patient off a leash note the direction in which they turn. While circling is readily apparent to most pet owners, turning predominantly to one direction is a more subtle clue to possible neurologic disease that will often not be noticed at home. The pet owner may be a tremendous help at motivating the pet to move during this phase of examination. Placing the patient on the floor in an enclosed room while the history is being obtained is a good time to begin observing gait and posture.
Evaluation of mentation
Evaluation of mentation can also begin with the patient on the floor while a history is obtained or reviewed. Observe how the pet interacts with its environment (your examination room), the pet owner and the veterinary staff. Keep in mind the differences in behavior expected between species, age of the pet and breed. Young animals and puppies/kittens are energetic and may be very willing to explore the exam room and play, while older pets are more content to lie by their owner's feet. Puppies that only want to sleep and are difficult to arouse or older dogs that compulsively walk throughout the room are examples of behaviors that are usually not appropriate. Cats are often very reluctant to walk in the exam room and often prefer to seek refuge under a chair. Placing a cat at the farthest distance in the room from their hiding place often stimulates them to move back to the place of safety, and their gait can be observed at this time.
The hands on portion of the neurologic examination begins with evaluation of postural reactions. For this portion of the examination it is very important to have an assistant to help restrain and support the patient. Many pet owners are able to assist during the examination, but assistance from veterinary staff is recommended if possible. Postural reactions evaluate a patient's understanding of their body position in space and require all components of the nervous system (peripheral nerves, spinal cord and brain) to be functioning properly for the test to be completed normally. For some postural reactions, such as hopping, wheel barrowing and extensor postural thrust some degree of strength is also required for the patient to complete the reaction. By beginning the hands on portion of the neurology examination with postural reaction testing the veterinarian and the patient can "get to know each other" in the least threatening manor for the pet.
Proprioceptive placing should be performed on all patients that permit this test. Care should be taken to support the pet to prevent leaning or falling when the limb being tested is lifted and the foot misplaced. This prevents integration of the vestibular system into the results and allows for more accurate results. I perform this test on the rear limbs first from behind the patient, with the patient facing away from me. After testing the rear limbs the front limbs are tested from the side of the patient. A normal response is the patient refusing to allow the foot to be misplaced, or rapidly replacing the foot after the foot is released by the examiner. Paying attention to the symmetry of the response between the right and left sides will allow even subtle differences to be observed
The hopping response can also be useful for detecting subtle evidence of asymmetry in symptoms in smaller patients. In small dogs and cats the entire animal is supported off the ground and the animal allowed to bear weight on the limb being tested. Lateral and forward movement is most useful for assessing patients, as medial hopping can be hard for many normal animals. In larger dogs lifting only one front or rear limb and moving the patient laterally can be performed. Lifting both limbs on one side of the body is the hemiwalking test and is also a way to test limb strength in larger dogs. As with all postural reaction testing, care should be taken to perform the testing consistently between the left and right sides of the patient to ensure the most reliable results.
If there are clear neurologic deficits present when testing proprioceptive placing and/or hopping there is no need to perform further postural reaction testing. However, if there are still questions about whether neurologic deficits are present, other postural reaction tests can be helpful. In my experience, placing reaction testing is especially useful when evaluating cats. Both visual and tactile placing can be assessed, but tactile placing should be tested before visual placing if possible. When testing cats I hold the patient with one front limb restrained against the pet's body with the test limb in a normal position and unrestrained. The head is extended with the other hand to prevent the cat from seeing the edge of the table and the cat is moved forward so the metacarpal area of the food touches the edge of the table. After several trials are performed, the opposite limb is tested. Holding the cat as far away from your body as possible produces a more accurate test. A positive/normal response is for the patient to reach for the top of the table when they feel their limb touch the edge of the table. Tactile placing tests sensory and motor pathways to the limb. The placing reaction can be repeated but this time the patient is allowed to see the table as they are moved toward the table edge. For visual placing the patient should reach for the table edge prior to touching the table. When testing visual placing I move the patient so that the table edge will hit the mid to upper portion of the limb. This often stimulates a stronger positive response. Tactile placing tests vision and motor function of the limb.
Reflex testing to the limbs is most accurately performed with the patient relaxed on their side, and use of an assistant is recommended. The most reliable myotatic reflex is the patellar (knee jerk, quadriceps) reflex. With the patient on their side, the upper limb is supported with the palm of the hand under the medial stifle and the patellar tendon is percussed with a neuro hammer. A normal response is a single, brisk kick of the lower limb as the quadriceps muscles contract. I test the ventral most rear limb as well with the limb flat against the floor, remembering that the response may not be as brisk because of the weight of the patient on the upper thigh and friction of the limb moving against the floor. If the pet raises the upper limb to expose the abdomen in a submissive posture, there will be too much tone in the limb to get an accurate response. In patients in this submissive posture testing the lower limb usually provides a more accurate response, as the lower limb will be relaxed even when the pet is in the submissive posture. Patellar reflex testing is then repeated by placing the pet in lateral recumbency on its other side with both the upper and lower limbs tested. The patellar reflex tests the sensory and motor components of the femoral nerve, which originates from spinal cord segments L4-L6.
With the patient still in lateral recumbency the withdrawal (flexor) reflexes of both the front and rear limbs can be tested. The upper limb is initially palpated and flexed so the tone of the muscles in the limb can be assessed. Many patients will flex the joints of the limb when the foot is touched, and in such patients no further stimulus of the foot is necessary. For others pinching the web of the toes is necessary. Start with your fingers and use the least amount of force necessary to stimulate flexion. If there is no initial response the toes themselves can be stimulated. The normal response is for the patient to flex all of the joints in the limb. Some patients with peripheral neuropathies can strongly flex the hip and stifle but have decreased flexion of the hock. Extension of the contralateral limb when testing withdrawal is a positive crossed extensor reflex, and indicates an upper motor neuron lesion when present. In the rear limb the withdrawal reflex tests primarily the sciatic (ischiatic) nerve and spinal cord segments L6-S1. If only the medial digit is stimulated the saphenous nerve (branch of the femoral nerve) may also be stimulated. In the front limb the radial, median and ulnar nerves provide sensory innervation to the foot and the musculocutaneous, axillary, median and ulnar nerves innervate the major flexor muscles of the front limb. These nerves originate from spinal cord segments C6-T1.
In some instances, placing a patient on their side produces high anxiety in the pet and they struggle excessively while being placed in this position. Consideration of the possible cause of a patient's neurologic symptoms should be taken into consideration when deciding how much effort to take to place a pet in lateral recumbency. For instance, a pet with a possible spinal trauma or intervertebral disc extrusion should not be allowed to struggle. In these patients patellar and withdrawal reflexes can be tested in the standing position. With the patient facing away from the examiner, the pelvic limb can be supported under the stifle so that the stifle can swing freely. With patience most pets will relax the limb and the patellar tendon can be struck to stimulate the reflex. Care must be taken to not impede movement of the limb or to attempt reflex testing in a limb in which the muscles are not relaxed. Pinching the web of the toes with the fingers when supporting the trunk of the body will also produce an accurate withdrawal reflex. If there are any questions about the accuracy of the results obtained, the reflexes should be repeated with the pet in lateral recumbency.
Various recording scales have been proposed to record observations in reflex testing. It must be remembered that reflex evaluation is subjective and may differ between observes. Therefore, from a clinical standpoint areflexia and hyporeflexia can be grouped together, as can normal reflexes and hyperreflexic responses. A weak or absent reflex indicates disruption of the reflex pathway and a lower motor neuron response. Conversely, a normal or exaggerated reflex indicates the reflex arc is intact.
The cutaneous trunci (panniculus) and perineal/anal reflexes also may provide useful clinical information. The cutaneous trunci reflex is stimulated by pinching the skin of the back beginning just cranial to the pelvis and gluteal muscles. The stimulus travels to the spinal cord via segmental sensory nerves, then travels up the cord to spinal cord segments C8 and T1. These spinal cord segments form the lateral thoracic nerve which stimulates contraction of the cutaneous trunci muscle. The cutaneous trunci reflex is most useful for determining the level of spinal cord injury in patients with moderate to severe motor impairment, and for assessing the integrity of the C8 and T1 nerve roots in patients with brachial plexus injuries. The perineal reflex is tested by stimulating the perineum or anus and observing for contraction of the anal sphincter. The pudendal nerve and spinal cord segments S1 and S2 are evaluated with perineal reflex testing. This reflex is usually recorded as present, hyporeflexic or absent.
Cranial nerve testing
The most clinically important cranial nerves (CN) are the optic (II), oculomotor (III), trigeminal (V), facial (VII), vestibulocochlear (VIII), hypoglossal (IX), vagus (X) and hypoglossal (XII). By observing the patient in the examination room vision (CN II) and balance (CN VIII) can be assessed. Observing the face and eyes for symmetry also evaluates CNs VII and III, IV and VI respectively. The pupillary light reflex evaluates CNs II and III and CNs V and VII are evaluated by testing the palpebral reflex. The menace response evaluates CNs II and VII. Cranial nerve VIII is further tested by observing for strabismus and/or nystagmus when the pet's head is elevated or they are placed upside down or on their side. The trigeminal nerve (CN V) is further assessed by testing facial sensation and evaluating jaw tone. As the mouth is opened the gag reflex is tested to evaluate CNs IX and X. Most patients will lick following stimulation of gag and motor control of the tongue (CN XII) can be observed.
Sensory testing is performed last during the neurology examination because this can be uncomfortable for the patient. Vertebral palpation should be performed only if there is no known history of trauma and should begin in the area of the vertebral column least likely to be painful. If neck pain is present in a young, toy breed dog flexion of the neck should not be performed because of the potential of atlanto-axial subluxation. A light stimulus is used initially, and then repeated palpation with increasing pressure can be used until the vertebral column is adequately assessed.
Sensory testing to the limbs need only be performed if there is no motor movement to the legs. Begin testing superficial pain by using the fingers on the web of the toe. If there is no response pressure can be applied with an appropriately sized hemostat to the toe web. If there is still no response pressure is applied to the toe itself and deep pain is tested. A positive response to sensory testing is behavioral recognition of the stimulus by the patient, such as vocalizing pain, turning toward the stimulus, or trying to escape. In the most stoic animals the only response may be that they stop panting or that their pupils dilate during the stimulus. It is vitally important not to confuse flexion or reflexive movement of the limb with the conscious recognition of pain, as this tests only the reflex pathways of the limb and not the integrity of the ascending sensory tracts in the spinal cord.