Some people with multiple sclerosis (MS) feel their symptoms worsen when they become overheated. When elevated body temperature impairs vision, it’s called Uhthoff’s phenomenon.
Uhthoff’s occurs because of damage to the optic nerve. It interferes with the transmission of signals between the eyes and 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 William 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
A 2011 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 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.
MS-related heat sensitivity doesn’t cause new symptoms, but it can aggravate existing symptoms. Besides vision problems, these can include:
- bladder problems
Treatment involves cooling your body temperature. If you’re outdoors on a hot or humid day, find a shady area to rest. If you can, stay indoors and take advantage of air conditioning or a fan. You could also take a cool bath or shower. And drink a cool beverage or use ice cubes to cool your body. Once you’ve cooled down, symptoms generally improve quickly.
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. Try to stay indoors and use an air conditioner or fan during times of extreme heat and humidity. This is especially helpful when exercising. Also avoid hot showers, baths, and saunas.
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, and 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’re thinking of relocating for health reasons, it’s a good idea to spend some time in a different climate first to see if it makes a difference.
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, see your doctor.