MS Signs vs. Symptoms: What is Uhthoff's Phenomenon?

by Lisa Emrich Patient Advocate

With summer approaching, I thought that Uhthoff’s phenomenon would be an appropriate topic for discussion in our MS Signs vs. Symptoms series.

What is the Uhthoff’s phenomenon?

Originally noted by Wilhelm Uhthoff in 1890, some patients with multiple sclerosis experience a “marked deterioration of visual acuity during physical exercise.” Observed in 4 of 100 MS patients, temporary and reversible optic symptoms (including blurriness, double vision, and blind spots) were induced by an increase in body temperature. This phenomenon is primarily associated with previous or ongoing optic neuritis.

Does Uhthoff’s phenomenon only involve vision?

A rise in body temperature (whether from exercise, a hot bath, illness, stress, or other causes) may cause other symptoms to appear or re-emerge in patients who have a demyelinating disease. It is not only vision which can be affected. For example, my legs become weak and ataxic when my body becomes overheated. I become extraordinarily fatigued which affects my physical and cognitive abitilies.

This is often called “heat intolerance” or “heat sensitivity.”

Some sources strictly associate with Uhthoff’s phenomenon only with visual symptoms, while others expand the description to include additional temporary deficits in body functions caused by damage to the central nervous system.

What is the “hot bath” test?

In the decades before magnetic resonance imaging (MRI’s) and other tests for multiple sclerosis, doctors would observe any changes in neurological symptoms occurring during or after a patient was exposed to a hot bath. The appearance or worsening of symptoms was used as evidence of demyelinating lesions or the presence of multiple sclerosis. These symptoms could involve motor, sensory, or visual function.

What causes Uhthoff’s phenomenon?

The exact cause or explanation of Uhthoff’s symptom is somewhat controversial. The rise in temperature is believed to interfere directly with the conduction of axons (which carry nerve signals), to release a chemical substance that interferes with conduction (such as serum calcium, heat shock proteins, or unidentified humoral substances), or both. In other words, we don’t really know for certain.

A simplified way of describing what happens in my own body is that the nerve signals feel as if they SLOW DOWN when I get overheated. When I say slow down, I really mean slow as in molasses slow. The cause of the rise in body temperature doesn’t seem to make much of a difference. My physical therapist says that even a rise in core body temperature of one degree Fahrenheit can cause symptoms to emerge or affect the body’s function.

If I experience Uhthoff’s phenomenon, do I have MS?

Just because you have experienced optic neuritis and may experience Uhthoff’s phenomenon, it doesn’t automatically mean that you have multiple sclerosis. However, evidence points to Uhthoff’s as a strong predictor of later development of MS.

In a 1991, 81 patients with a first attack of isolated optic neuritis, 40 patients who also had Uhthoff's symptom (Group 1) and 41 patients who didn’t (Group 2), were studied. The visual evoked potential testing from both groups did not differ significantly. However, the MRI scans of patients in Group 1 showed significantly more abnormal results. Treatment with steroids did not affect Uhthoff’s phenomenon, which was also associated with a higher incidence of recurrent optic neuritis. Overall 43% of patients (35 out of 81) developed MS within 3.5 years, significantly more from Group 1.

What if a patient’s symptoms improve when they get hot?

This is called an Inverse Uhthoff’s syndrome. An unexpected improvement is experienced when the body temperature rises. It has also been described as a worsening of symptoms which occur when the body temperature drops.

What can I do to prevent or relieve the symptoms of Uhthoff’s phenomenon?

Keep in mind that the Uhthoff’s phenomenon is a temporary (transient) condition. Once your body temperature returns to normal, the symptoms generally will subside. This situation can also be referred to as a pseudoexacerbation. It is not a true relapse of your MS.

One way to avoid the effects of Uhthoff’s phenomenon is to keep your body temperature at a comfortable level especially during the summer heat. These same strategies can help when you exercise.


Stutzer P, Kesselring J. Wilhelm Uhthoff: A Phenomenon, 1853 to 1927. (pdf) The International MS Journal. 2008 Sep;15(3):90-3.

Scholl GB, Song HS, Wray SH. Uhthoff's symptom in optic neuritis: relationship to magnetic resonance imaging and development of multiple sclerosis. Ann Neurol. 1991 Aug;30(2):180-4.

Guthrie TC, Nelson DA. Influence of temperature changes on multiple sclerosis: critical review of mechanisms and research potential. J Neurol Sci. 1995 Mar;129(1):1-8.

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Additional studies can be found by searching for Uhthoff's phenomenon.

Lisa Emrich
Meet Our Writer
Lisa Emrich

Living with multiple sclerosis and rheumatoid Arthritis, Lisa Emrich is an award-winning, passionate patient advocate, health writer, classical musician, and backroad cyclist. Her stories inspire others to live better and stay active. Lisa is author of the blog Brass and Ivory: Life with MS and RA and founder of the Carnival of MS Bloggers. Lisa frequently works with organizations in support of better policies, patient-centered research, and research funding. Lisa serves on HealthCentral’s Health Advocates Advisory Board, and is a Social Ambassador for the MSHealthCentral Facebook page.