Experiencing a sudden change in symptoms can be unsettling, but it’s important to know that not every worsening of symptoms represents a true MS relapse. A true relapse reflects new inflammatory activity in the central nervous system and causes new neurologic symptoms or a clear worsening of previous ones that persist for at least 24–48 hours, without another explanation such as infection or fever. These relapses often correspond with new lesions seen on MRI and may sometimes require treatment, such as corticosteroids, to help shorten the duration of symptoms—although mild relapses may simply be monitored by your care team.
In contrast, a pseudo-relapse is a temporary worsening of existing symptoms triggered by external factors such as infection, elevated body temperature (heat sensitivity), physical exhaustion, emotional stress, or even poor sleep. One well-known example is Uhthoff’s phenomenon, which occurs when small increases in body temperature—caused by hot weather, exercise, fever, or even a hot shower or hot tub—temporarily worsen neurologic symptoms, such as vision changes or weakness. Historically, clinicians sometimes used hot baths or hot tubs to observe this effect as supportive evidence of MS, but modern diagnosis relies on MRI and clinical evaluation rather than heat testing. Importantly, pseudo-relapses do not involve new immune-system–driven damage and typically improve once the trigger resolves. Because management differs between true relapses and pseudo-relapses, distinguishing between the two is important.
When should you call your MS team? You should contact your MS care team if you notice new or significantly worsened symptoms lasting longer than 24 hours—especially if there is no obvious trigger such as heat exposure or a recent illness. Please also reach out if symptoms develop suddenly over hours or overnight, or if they are severe or interfere with daily function, such as vision changes, difficulty walking, significant weakness, or problems with balance. Even if you suspect a pseudo-relapse, it is always reasonable to call—your care team can help assess whether this represents a true relapse, rule out treatable causes like infection, and guide next steps. Prompt communication helps ensure timely evaluation, support, and peace of mind. If there is a very sudden or severe neurologic change, call 911 immediately.
Managing Heat Sensitivity: For patients who notice symptoms worsen with heat, simple strategies can help minimize discomfort: stay hydrated, use cooling vests or fans, avoid prolonged exposure to hot environments (including hot tubs), and pace activities during warmer parts of the day. Remember, this does not indicate new damage or disease progression—just temporary signal disruption in previously affected nerves.