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This issue of the Archives contains a report of four cases of multiple sclerosis in which impaired visual acuity was further reduced by heat and exercise (Uhthoff's symptom). The authors venture no explanation and frustrate the reader who asks ``Why?'' Earlier writers, also, have merely recorded the observation or have halfheartedly offered a feeble theory. This phenomenon seems not universally recognized by neurologists or by ophthalmologists, although some of us have observed it clinically for many years and relegated it to the category of the unexplained. Since those patients who have been examined carefully have shown enlargement of central scotomas, the site of the disorder appears to be in the optic nerves rather than in the cerebral hemispheres.
Heat and exercise not only impair vision in some susceptible victims of multiple sclerosis, but also intensify the weakness of the extremities and the ataxia. Explaining a phenomenon in a disease of
R. CW. Uhthoff's Symptom. Arch Ophthalmol. 1964;72(2):151. doi:10.1001/archopht.1964.00970020151001
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