A description of the clinical picture of multiple sclerosis (MS) includes symptoms, the patient's complaints, and signs, what the doctor finds in an examination, such as a change in the knee-jerk reflex test. Together, they are called "findings" and are the principal clues to accurate diagnosis and eventual prognosis.
Symptoms and signs are most commonly believed to be the result of MS lesions causing disturbances in electrical conduction in one or more of three general sites in the central nervous system - the optic nerve, the brain stem-cerebellum, and the spinal cord. As each area controls particular functions of the central nervous system, the location of the lesion will determine the type of attack. For example, an optic nerve lesion may cause blurred vision, blind spots, or a decrease in brightness. A brain stem-cerebellar lesion can cause dizziness or double vision or balance and coordination trouble. Spinal cord lesions give rise to symptoms such as weakness or numbness of the limbs. Occasionally, signs and symptoms are caused by lesions in a fourth area, the cerebrum. This area, however, remains something of a puzzle.
Although the pathological lesions of MS are very common there, cerebral signs and symptoms are relatively rare. This discrepancy between lesions and clinical signs and symptoms is one of the great curiosities of MS; many, possibly most, MS plaques are "silent." In fact, a January 1986 study at the Neurologic Institute of the Millard Fillmore Hospital in Buffalo, New York, found that 75 percent of all lesions were "clinically silent."