Persistent neurological deficit precipitated by hot bath test in multiple sclerosis.

For a half century, the hot bath test has been used as a "diagnostic test" in multiple sclerosis. The appearance of new neurological signs or aggravation of preexisting signs generally is transient, with resolution on return of body temperature to normal. We have observed four patients, however, with considerable and prolonged neurological debilitation after hot bath testing. We suggest caution in the application of such testing.