Uhthoff's Phenomenon - Clinical Significance

Clinical Significance

Many patients with MS experience increased fatigue and other symptoms such as pain, concentration difficulties, and urinary urgency when exposed to heat. As a result, many patients with MS tend to avoid saunas, warm baths, and other sources of heat or wear ice or evaporative cooling apparel in the form of vests, neck wraps, arm/wrist bands, and hats.

Peripheral nerve studies have shown that even a 0.5°C increase in body temperature can slow or block the conduction of nerve impulses in demyelinated nerves. With greater levels of demyelination, a smaller increase in temperature is needed to slow down the nerve impulse conduction. Exercising and performing activities of daily living can cause a significant increase in body temperature in individuals with MS, especially if their mechanical efficiency is poor due to the use of mobility aids, ataxia, weakness, and spasticity. However, exercise has been shown to be helpful in managing MS symptoms, reducing the risk of comorbidities, and promoting overall wellness.

Taking advantage of the cooling properties of water may help attenuate the consequences of heat sensitivity. In a study done by White et al. (2000), exercise pre-cooling via lower body immersion in water of 16-17°C for 30 minutes allowed heat sensitive individuals with MS to exercise in greater comfort and with fewer side effects by minimizing body temperature increases during exercise. Hydrotherapy exercise in moderately cool water of 27-29°C water can also be advantageous to individuals with MS. Temperatures lower than 27°C are not recommended because of the increased risk of invoking spasticity.