Uhthoff’s Phenomenon: Understanding OverheatingShare on Pinterest
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Some people with multiple sclerosis (MS) feel their symptoms worsen when they become overheated. When elevated body temperature impairs vision or other MS symptoms, it’s called Uhthoff’s phenomenon.

Uhthoff’s occurs because of previous damage to myelinated nerves due to MS. It interferes with the transmission of nerve signals to the brain. Symptoms include blurry or reduced vision, and it’s often one of the first symptoms of MS.

Uhthoff’s phenomenon is sometimes called “Uhthoff’s syndrome” or “Uhthoff’s sign.” The condition was named for Wilhelm Uhthoff, a German professor of ophthalmology who lived from 1853 to 1927.

MS is a chronic disease in which the immune system attacks myelin, the protective covering surrounding nerve cells in the central nervous system (CNS).

Inflammation damages the nerve cells and causes lesions and scar tissue to form. This damage impairs the ability of the CNS to send signals to the rest of the body.

Symptoms of MS vary depending on the location of the lesions. Some symptoms include:

  • vision problems
  • bladder dysfunction
  • difficulty with balance and coordination
  • fatigue
  • muscle weakness
  • numbness or tingling
  • cognitive changes

A 2018 study reported that between 60 and 80 percent of people with MS experience heat sensitivity.

Demyelinated fibers in the CNS are hypersensitive to a rise in body temperature. This makes it more difficult for the body to receive internal signals. This can result in a worsening of MS-related symptoms and cause blurred vision.

The good news is that heat sensitivity and the related worsening of MS symptoms are only temporary. This is called pseudo-exacerbation. It doesn’t mean new lesions, lasting neurological damage, or a more rapid progression of MS.

Uhthoff’s is only temporary, so there’s no need to panic if you develop symptoms. But if your vision is seriously impaired, ask someone to assist you in getting to a safe place to rest and cool off.

MS-related heat sensitivity doesn’t cause new symptoms, but it can aggravate existing symptoms. Besides vision problems, these can include:

  • fatigue
  • numbness
  • weakness
  • bladder problems

Treatment involves cooling your body temperature. Once you’ve cooled down, symptoms generally improve quickly.

Ways to cool off during Uhthoff’s

  • When outdoors, find a shady area to rest or head indoors to a fan or air conditioning
  • hydrate with cool water
  • take a cool bath or shower
  • apply a cold compressor ice pack to your neck, wrists, and feet
  • Have a cooling vest or scarf handy for when you may be in a hot area
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Fever can also cause Uhthoff’s. When you have a fever, the remedy is to treat the underlying cause.

Medical intervention isn’t necessary for symptoms of Uhthoff’s. If you’ve experienced it before, you’ll know what to expect. But it’s easy to confuse heat-related symptoms with other medical emergencies.

Seek medical attention if:

  • you’ve never experienced heat-related symptoms of MS before
  • you’re uncertain that your symptoms are Uhthoff’s or MS-related
  • you have accompanying symptoms unrelated to MS
  • your symptoms don’t improve after you’ve cooled down

To avoid Uhthoff’s phenomenon, the key is to avoid overheating in the first place.

When indoors:

  • Use an air conditioner or fan during times of extreme heat and humidity. This is especially helpful when exercising.
  • Avoid hot showers, baths, and saunas.

When outdoors:

  • Try to stay in the shade and avoid intense exercise.
  • Use cooling products such as cooling vests, neck wraps, and portable fans.
  • Enjoy icy beverages.
  • Avoid hot tubs and swimming pools heated above 85°F (29°C).

In some cases, MS and Uhthoff’s don’t go together. If you’re not sensitive to the heat, there’s no need to avoid activities you enjoy.

While heat and humidity can trigger a wide range of MS-related symptoms, so can cold weather. High humidity or cold temperatures can trigger involuntary muscle spasms or stiffness, called spasticity.

If you have heat- or cold-related symptoms of MS, it’s best to avoid exposure to any extreme temperature, if you can. If you’re thinking of relocating for health reasons, you may want to spend some time in a different climate first to see if it makes a difference for you.

Uhthoff’s phenomenon is easy to treat and doesn’t mean your MS symptoms are worsening. But if you’ve never experienced symptoms of Uhthoff’s or of MS, talk with your doctor.