| Uhthoff's phenomenon | |
|---|---|
| Other names | Uhthoff's syndrome, Uhthoff's sign, Uhthoff's symptom |
 | |
| Wilhelm Uhthoff | |
| Specialty | Neurology |
| Symptoms | fatigue,pain,urinary urgency, worseoptic neuritis |
| Causes | high body temperature, causes longer inactivation ofvoltage-gated sodium channels |
| Diagnostic method | based on symptoms |
| Differential diagnosis | degeneration of condition ofmultiple sclerosis |
| Prevention | keeping cool, use of cool clothing |
| Treatment | cool clothing |
| Medication | none |
| Prognosis | typically completely reversible |
| Frequency | 60-80% of people withmultiple sclerosis |
| Deaths | 0 |
Uhthoff's phenomenon (also known asUhthoff's syndrome,[1]Uhthoff's sign,[1] andUhthoff's symptom) is the worsening ofneurologicsymptoms inmultiple sclerosis (MS) and otherdemyelinating diseases when the body is overheated. This may occur due tohot weather,exercise,fever,saunas,hot tubs,hot baths/showers, and hot food and drink. Increasedtemperature slowsnerve conduction, but the exact mechanism remains unknown. With an increased body temperature,nerve impulses are either blocked or slowed in a damaged nerve. Once the body temperature is normalized, signs and symptoms typically reverse.[citation needed]
Symptoms of Uhthoff's phenomenon occur when exposed to heat, and include:
Uhthoff's phenomenon is caused by a raisedbody temperature.[1] This may be caused by:
The exact mechanism of Uhthoff's phenomenon is unknown. It causes a decrease in the speed ofaction potentials in thecentral nervous system (CNS).[1][6] Heat may increase the time whenvoltage-gated sodium channels are inactivated, which delays furtheraction potentials.[6][7] This is worsened by thedemyelination caused by MS.[7] Other theories have considered the role ofheat shock proteins and changes toblood flow.[1]
Peripheral nerve studies have shown that even a 0.5 °C increase in body temperature can slow or block the conduction ofnerve impulses indemyelinated nerves. With greater levels of demyelination, a smaller increase in temperature is needed to slow down the nerve impulse conduction.[8] Exercising and normal daily activities can cause a significant increase in body temperature in individuals with MS, especially if their mechanical efficiency is poor due to the use ofmobility aids,ataxia,weakness, andspasticity.[9] However, exercise has been shown to be helpful in managingMS symptoms, reducing the risk of comorbidities, and promoting overall wellness.[10]
Diagnosis of Uhthoff's phenomenon isclinical and based on symptoms when it occurs in a person who is already diagnosed with MS.[1] The main differential diagnosis is a more serious worsening of MS symptoms.[1]
Many patients with MS tend to avoidsaunas, warmbaths, and other sources of heat. They may wearice or evaporative cooling clothes, such asvests,neck wraps,armbands,wristbands, andhats. Taking advantage of the cooling properties ofwater may help attenuate the consequences of heat sensitivity. Exercise pre-cooling via lower body immersion in water of 16–17 °C for 30 minutes may allow heat sensitive individuals with MS to exercise more comfortably with fewer side effects by minimizing body temperature increases during exercise.[9]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 invokingspasticity.[10]
Uhthoff's phenomenon is a temporary problem, and typically completely reverses once body temperature returns to normal.[2][8] This may take up to 24 hours.[1]
Uhthoff's phenomenon may affect any person with ademyelinating disease.[1] This is most commonly MS, but it may also occur withneuromyelitis optica spectrum disorder[1][3] orGuillain-Barré Syndrome. It affects between 60% and 80% of people with MS.[1][3]
Uhthoff's phenomenon was first described byWilhelm Uhthoff in 1890 as a temporary worsening of vision with exercise in patients withoptic neuritis.[1][11] Later research revealed the link between neurological signs such as visual loss and increased heat production and Uhthoff's belief that exercise was theetiology of visual loss was replaced by the conclusions of these later researchers stating that heat was the prime etiology.[12]