Fluctuations of visual evoked potential amplitudes and of contrast sensitivity in Uhthoff's symptom

Visual evoked potentials (VEPs) to pattern reversal and psychophysical contrast sensitivity (CS) were tested in five patients with Uhthoff's symptom before and after exercise. Four of the cases were related to a demyelinating disease and one patient had a severe brain injury. Uhthoff's symptom occurred also in neuropathies without previous clinical neuritis and in eyes with normal latency time of the VEPs. A depression of CS was observed by all five patients after exercise; a transient "overshoot" of CS following the depression was present in three of the patients. VEP amplitudes were reduced by exercise in three cases. Responses by stimulation with small checks were more affected. Paradoxical increased VEP amplitudes after exercise in the presence of a loss of psychophysical CS were found in one case.