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WSVA7-0364
NEUROLOGY
THE FELINE NEUROLOGIC EXAMINATION - NEED TO KNOW APPROACH
S. Platt1
1College of Veterinary Medicine- University of Georgia, Small Animal Medicine & Surgery, ATHENS, USA
THE FELINE NEUROLOGIC EXAMINATION - NEED TO KNOW
Simon R. Platt BVM&S MRCVS Dipl. ACVIM (Neurology) Dipl.ECVN
University of Georgia, Athens, GA. srplatt@uga.edu
A neurological examination is easily integrated into a routine physical examination. The objectives of the neurological examination are to confirm if there is a neurological abnormality and to specifically localize the abnormality within the nervous system. In conjunction with the history, signalment, presenting complaint
and the physical examination, the neurological lesion localization is a piece of a jigsaw essential to creating
a list of differential diagnoses for the disease. However, caution must be used as some manipulations necessary for the neurological examination could exacerbate problems such as spinal cord disease.
Observation
Observation of the dog or cat is essential as it allows evaluation of the mentation, posture, attitude, and
gait. Changes in mentation (level and content of consciousness) are revealed by a history of personality change, change in awareness of surroundings, and inappropriate behavioural responses. Consciousness
is a function of the brainstem (responsible for arousal) and the cerebral cortex (responsible for content and regulation). The evaluation of the state of consciousness can classify the patient as depressed, demented or obtunded, delirious, stuporous and comatose.
Cranial nerves
Simplistically, cranial nerve dysfunction may indicate a central nervous system (CNS) lesion (brainstem disease) or a peripheral lesion (affecting the cranial nerves after they have exited the brainstem and course through the skull). Evaluation of the cranial nerves should follow observation and palpation, with particular attention paid to normal functions of eye movement, head movement, blinking, jaw and tongue movement and general symmetry of the head. Initially an ophthalmic exam should be performed, which will assist with the evaluation of the optic (CN II), oculomotor (CN III), trochelar (CN IV), and abducens (CN VI) nerves.
The menace response
1. How to perform – obscure the vision in one eye and make slow threatening hand gesture toward the other eye.
2. How to interpret - this is a learned response, not a reflex, to a perceived threat, which evaluates CNs II and VII (responsible for innervation of the orbicularis oculi muscle which closes the eyelids), as well as the central visual pathways and the cerebellum. Normal function is demonstrated by a blink or retraction of the globe in response to the threat. To localize the lesion, other cranial nerve tests would be required.
The pupillary light reflex
1. How to perform – shine a bright light in each eye to evaluate the response of the pupil.
2. How to interpret – this is a reflex. Light is sensed by CN II; parasympathetic fibers of CN III cause contraction of the iris muscle with direct and indirect simulation. The pupil is also innervated by sympathetic fibres responsible for dilation, which have their origin
in the thalamus and send fibres down the cervical spinal cord to
the T1-T3 spinal nerve roots, before they ascend up the neck and through the middle ear. A resting inequality in pupil size is termed anioscoria; to determine which pupil is abnormal, the animal should be evaluated in the light and dark. In the dark, a sympathetic lesion will mean the affected pupil will not be able to fully dilate. In the light, a parasympathetic lesion will mean the affected pupil will not be able to fully constrict. Animals with sympathetic lesions will often demonstrate miosis in accompaniment to third eyelid protrusion and enophthalmus; a condition called Horner’s syndrome.
The palpebral reflex
1. How to perform – touch the medial canthus of the normal eyelid and watch response.
2. How to interpret – the normal eyelid should close. Cranial nerve V (trigeminal nerve) is responsible for facial sensation, whereas the motor response to facial sensory stimulation is generally provided by the facial nerve (CN VII). Facial paresis presents as a drooping of the facial muscles, most notably the lips and the eyelids. It may also be detected as a reduction or absence in the blink response.
Evaluation of jaw tone
1. How to perform – observe patient for a dropped lower jaw and / or an inability to eat. Assess the strength of the jaw safely by manually opening the mouth and evaluating the resistance to opening.
2. How to interpret – the mandibular branch of CN V provides motor function to the jaw. A dropped lower jaw or the inability to chew can indicate damage to CN V
Postural reactions
1. How to perform – a leg is placed in an abnormal position and a correcting response by the animal is observed. Knuckling the toes over whilst supporting the body can be done to evaluate how long it takes for the animal to correct. Alternatively, a piece of paper may be placed under each foot and slowly moved sideways, to see if the animal returns its foot to the standing position. Other postural reactions include wheelbarrowing, hopping, hemistanding and extensor postural thrust.
2. How to interpret – conscious proprioception is the patient’s awareness of limb position and movement without visual information. When the knuckling test is performed, an abnormality is indicated by a delay or absence of the response. The sensory branch of proprioception is carried from the skin, muscle and joints of the leg through the spinal cord and brainstem to the sensory motor cortex, where the brain responds by sending messages back
An Urban Experience
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