Diurnal variations in vision and relations to circadian melatonin secretion in multiple sclerosis.

It has long been recognized that symptoms of multiple sclerosis (MS) wax and wane with fluctuations occurring on an hour to-hour basis throughout a 24 hour period. It has been proposed that changes in circadian core body temperature, which alter axonal conductivity, may account for the fluctuations of symptoms in MS. A 51-year-old man with MS is reported in whom visual acuity deteriorated throughout the course of the day only to improve again at night between 10:00 p.m. and 2:00 a.m. These changes in vision were unrelated to rest or physical activity, but appeared to coincide with the circadian secretion of melatonin which is coupled to the circadian temperature rhythms. Since melatonin lowers body temperature, it is hypothesized that the nocturnal rise in melatonin secretion was related to improvement in vision in this patient. This hypothesis is supported by the observation that administration of melatonin (3 mg, orally) at 2:00 p.m., when the patient experienced severe blurring of vision, resulted within 15 minutes in a dramatic improvement in visual acuity and in normalization of the visual evoked potential latency after stimulation of the left eye. Moreover, since the pineal gland is a thermoregulatory organ which functions to prevent excessive rise of body temperature, it is possible that since MS is associated with dysfunction of the pineal gland, these patients may experience diminished capacity to eliminate heat at rest or during physical activity with resultant elevation of body temperatures which may further compromise neurologic functions by causing failure of axonal conduction.