[Long-lasting and isolated Uhthoff's phenomenon after effort preceding multiple sclerosis]. / Phénomène d'Uhthoff lié à l'effort, isolé, précédant une sclérose en plaques.

INTRODUCTION: Described in 1890, Uhthoff's symptom corresponds to a transient blurred vision provoked by physical exercise or an increase of temperature. It is a frequent symptom occurring during the course of multiple sclerosis. PATIENTS AND METHOD: We report here four cases of patients presenting isolated Uhthoff phenomenon preceding multiple sclerosis by several years. RESULTS: These four patients presented transient neurological symptoms induced by intensive sporting activity for 1 to 6 years before diagnosis of multiple sclerosis. These symptoms were often visual but sometimes motor or sensorial. All symptoms appeared above a certain threshold specific to each patient, after 15 to 30minutes of intense physical exercise (bike, running or handball) and all disappeared after a few minutes to one hour rest with full recovery to baseline. DISCUSSION: Uhthoff's phenomenon is explained by a conduction block. It is due to axonal demyelization that provokes a reorganization of sodium channels induced by a decrease in a safety factor highly sensitive to temperature, or by release of soluble blocking substances (oxide nitric or cytokines). CONCLUSION: Without being specific, this symptom is strongly suggestive of this disease. Our case reports confirm the existence of "infraclinic multiple sclerosis".