Effects of Body Temperature Lowering on Visual Evoked Potentials in Patients with Multiple Sclerosis

Abstract

Objective: Aggravation of neurologic symptoms in patients with multiple sclerosis (MS) due to heating is well known. This phenomenon, known as Uhthoff phenomenon (UP), is explained by transient conduction block in demyelinated nerve fibers and transected axons. The threshold of conduction block dependent on temperature is probably proportional to the degree of demyelination or axonal injury. On the other hand, about half of all patients reported improvement in a cold bath (anti-UP effect). This study aimed to assess the effects of body cooling on clinical parameters [neuro-opthalmologic examination and contrast sensitivity in visual acuity/Sloan letter test, and the Expanded Disability Status Scale (EDSS)] and electrophysiologic measurements [visual evoked potentials (VEP)] in patients with MS previously clinically affected by optic neuritis. Materials and Methods: Twenty patients who described a UP or anti-UP effect with definite MS according to the McDonald and Poser criteria were enrolled in the study. Before the cooling process, all patients with a history of optic neuritis (at least once) were examined clinically, neurologically and neuro-ophthalmologically, and electrophysiologically. Body cooling was achieved using a “Medivance Arctic Sun Temperature Management System” and the body temperature was decreased by about 1 °C. After that, all patients were re-evaluated clinically and electrophysiologically. Results: After the cooling process, P100 latency significantly shortened at the 1st, 6th and 24th hours (p<0.001, p<0.001, p<0.001) and EDSS scores improved significantly (p<0.001). Visual acuity, including contrast sensitivity and color vision, significantly improved in both affected and unaffected eyes (p<0.001). Conclusion: These results suggest that heat caused a conduction block in demyelinated or transected axons in the visual pathways. Our results also demonstrate that the cooling process had beneficial effects on clinical disability scores (EDSS) and the visual system based on clinical and electrophysiologic (VEP) evaluations. These findings suggest that the cooling process may be used for symptomatic therapy and increasing life quality of patients with MS.

Keywords

• multiple sclerosis
• visual evoked potentials
• cooling effect
• uhthoff’s phenomenon