Uhthoff Symptom also referred to as Uhthoff Phenomenon does not display solely in Multiple Sclerosis patients, however, it was the principal diagnostic test for multiple sclerosis until the 1980’s when more accurate test methods became available.

Avoiding an unwanted heatwave Reaction, stay out of the summer sun Uhthoff Ssymptom

The patient will show a worsening of symptoms with an increase in body temperature. The temperature rise may be the result of exercise, a hot bath, or the prevailing climatic conditions. Most associated with Optic Neuritis this may demonstrate with or without multiple sclerosis. In one study, patients exhibiting Uhthoff’s phenomenon without multiple sclerosis were found to be more likely to develop MS than patients with Optic Neuritis who didn’t didn’t display Uhthoff’s Symptom.

MS Sign

An increase in heat can worsen many Multiple Sclerosis symptoms and cause new ones to appear. As well as Optic Neuritis it is most often seen to exacerbate MS fatigue.

It is thought, and these are just theories, that heat may affect serum calcium, circulatory change, heat shock proteins, and the most popular theory is the blockade of ion channels.

Uhthoff’s Symptom temperature sensitivity

I prefer the explanation, discussed on the fatigue page,  that demyelinated nerves suffer a performance drop when used a lot and the associated heat probably worsens this degradation.

A couple of anecdotal examples spring to mind:

  1. In the early days of living with MS; I still had the energy to attempt some physical work and I decided, against my better judgement, that the garden needed weeding. It was a lovely warm late-spring day so I ventured out to the garden shed and set about tidying the flower border. I managed only 15 or 20 minutes before my vision started to become blurry. I had to retreat to the house and take a seat for half an hour. My vision cleared so, undaunted, I set about the weeding again. Again, I lasted about fifteen minutes before the eyesight failed.
  2. I always enjoy a hot, relaxing soak in the bath. I was aware that many MSers don’t share my pleasure because of the heat intolerance. But, I was lucky; or I thought I was! On one occasion, I had been enjoying my little pleasure and having completed my ablutions I rose to step out of the bath, I got as far as the bathroom mat, where I intended to towel myself dry, when my legs rebelled. I didn’t fall, I just gently sank to the floor and found I could not get back up. I could not even site up or crawl. So I lay, naked, on the bathroom floor for a full fifteen minutes when my legs showed signs of some activity. I managed to stand, very unsteadily, and hobble to my bedroom and collapse on the bed. I remained there for the next hour before I felt strong enough to venture downstairs.

Interesting Observation

A hot sticky July afternoon, I was checking my blog, as one does, and notice that this page was top of my “popular posts” which MUST be related to the ambient temperatures we are experiencing today. If you, like me, are suffering in the summer heat then you have my sympathies.

I also find that I am not only sensitive to extremes of heat, but also, and perhaps more so, I find extremes of cold just as debilitating. Finding a happy medium is becoming increasingly difficult.


  • Wearing of a cooling vest
  • Cool bath or shower


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