The Uhthoff phenomenon describes a temporary worsening of neurological function in patients with multiple sclerosis (MS) in response to an increase in core body temperature. The phenomenon was originally observed in connection with impaired visual function after physical exertion in patients with MS. Subsequent observations showed that the same physiological mechanism responsible for visual dysfunction during heat exposure is also responsible for a variety of other neurological symptoms in patients with MS[^2].
Epidemiology
Approximately 80 % of patients with multiple sclerosis are affected by the Uhthoff phenomenon[^3].
Pathophysiology
It is assumed that an increase in temperature temporarily impairs conduction in demyelinated axons. The reversible worsening of neurological symptoms is therefore a "pseudorelapse," since the symptoms are triggered by physical phenomena rather than by inflammatory activity, as in an MS relapse. Studies of peripheral nerves have shown that an increase in body temperature of just 0.5 °C can slow or block impulse transmission in demyelinated nerve fibers. The more advanced the demyelination, the more temperature-sensitive the nerve fibers become[^4].
History
The Uhthoff phenomenon was named after the German ophthalmologist Wilhelm Uhthoff, who described the phenomenon as early as 1890[^1].