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Answered on: 7/18/2012
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Q :
Why do I cry when I'm overheated (Uhthoff's)? It seems to be an automatic response, as I'm not upset.
A :
This seems to be an interesting intersection of two issues that can affect people with MS. The first is spontaneous crying or laughing which is called “pseudobulbar affect”. (The older and more unfortunate term was pathological crying/laughter). This uncontrollable behaviour is felt to be the abnormal release of an automatic reflex in the brainstem circuitry. Similar to the way reflexes in the arms and legs can be brisker than normal in MS; the reflex systems in the brainstem controlling the movements for crying or laughing can be triggered more easily. As such, people can report that they laugh or cry at the slightest trigger, or even in situations without any emotional context at all as the question writer reports.
The second issue is Uhthoff’s phenomenon, which is the emergence of symptoms when someone with MS is overheated. A common example is noting blurred vision in an eye that was previously affected by optic neuritis after a hot shower. Hot tubs, spas or vigorous exercise which raises body temperature can also produce similar symptoms. Sometimes this is can be a persistent problem in some people throughout the hot summer months. Uhthoff’s phenomenon occurs because with increased temperature, protein chemical reactions speed up, causing increased energy demands. Demyelinated axons are not able to keep up with the demand, so nerve transmission slows and symptoms reappear. When the person cools down, the symptoms disappear again. In the case of the writer, it would seem that her pseudobulbar symptoms are being brought on by overheating.
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