Which phenomenon describes symptom worsening with increased core temperature in multiple sclerosis?

• A. Lhermitte sign
• B. Uhthoff phenomenon
• C. Heat intolerance
• D. Nystagmus

Answer: (B)

In MS, symptoms can temporarily worsen when body temperature rises because heat impairs the conduction of nerve impulses along already demyelinated fibers. This makes signals travel more slowly or fail to transmit, leading to new or intensified symptoms during fever, exercise, or hot environments. This temperature-related decline in function is known as the Uhthoff phenomenon. It’s typically reversible with cooling or rest, which helps nerve conduction return toward baseline. Other options describe different signs not tied to temperature: for example, a neck-flexion–triggered electric shock sensation, involuntary eye movements, or a general term for sensitivity to heat, none of which specifically capture the temperature-dependent symptom worsening seen in MS.