The Uhthoff phenomenon describes a transient worsening of neurological functions in patients with Multiple Sclerosis (MS) in response to an increase in the core temperature of the body. Originally, the phenomenon was observed in connection with deteriorated visual function following physical exertion in MS patients. Later observations showed that the same physiological mechanism responsible for visual dysfunctions during heat exposure is also responsible for a variety of other neurological symptoms in MS patients[^2].
Epidemiology
About 80% of Multiple Sclerosis patients are affected by the Uhthoff phenomenon[^3].
Pathophysiology
It is assumed that an increase in temperature temporarily worsens the conductivity of demyelinated axons. Therefore, the reversible neurological symptom worsening is a "pseudo-relapse", as the symptoms are triggered by physical phenomena, not by inflammatory activity as in an MS relapse. Studies on peripheral nerves have shown that even an increase in body temperature of 0.5°C can slow down or block the impulse transmission in demyelinated nerve fibers. The more advanced the demyelination, the more temperature-sensitive the nerve fibers become[^4].
Historical
The Uhthoff phenomenon was named after the German ophthalmologist Wilhelm Uhthoff, who described the phenomenon as early as 1890[^1].