Heat sensitivity in people with Multiple Sclerosis

Studies report that about 60 to 80% of people diagnosed with multiple sclerosis show excessive sensitivity to heat. People with this neurological disorder experience a temporary exacerbation of their existing symptoms and also new disturbing symptoms when they are exposed to elevated temperatures. They are sensitive to even a slight increase in their core body temperature (0.25°C to 0.5°C) that may be due to physical exercise or a warmer environment.In many people with Multiple Sclerosis, the disease presents with intermittent periods of relapses and remissions. But the heat sensitivity causing exacerbation of symptoms is different from relapses. The problem is actually a ‘pseudo-exacerbation’ of the symptoms. Increase in temperature as such does not cause any nerve damage. Most people with MS can actually figure out their intolerance to heat and they are aware of the fact that their symptoms get worse with increasing temperature.

Increase in temperature worsens the symptoms of MS

Most of the symptoms of MS are due to the impaired nerve impulse conduction and with an increase in temperature the symptoms worsen in the affected people.

  • Wilhelm Uhthoff in 1890 described the peculiar phenomenon of ‘temporary worsening of symptoms with exercise’ in optic neuritis patients. Optic neuritis is a condition affecting the eyes.
  • Fatigue is a common symptom and it is seen in nearly 70% of people with Multiple Sclerosis. Premature fatigue occurs in people with Multiple Sclerosis when they are exposed to even a slight increase in temperature. Weakness, especially affecting the limbs is also a symptom that is perceived during or aggravated by a temperature rise.
  • Central pain is another common symptom that worsens with an increase in temperature. Studies propose that the reason behind this may be the damage caused to the thalamus and the spinothalamic-cortical pathways leading to thermo-regulatory dysfunction. Numbness is another symptom that worsens with rising core body temperature.
  • Cognitive functions in Multiple Sclerosis patients are also sensitive to heat. Memory problems, judgment difficulties, concentration difficulties and problems with other cognitive skills like language comprehension are more pronounced with the increase in body temperature. A recent study pointed out that people with MS demonstrated worsening of cognitive functions in warmer days.  source


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