Uhthoff's phenomenon (also known as Uhthoff's syndrome, Uhthoff's sign, and Uhthoff's symptom) is the worsening of neurologic

symptom Signs and symptoms are diagnostic indications of an illness, injury, or condition. Signs are objective and externally observable; symptoms are a person's reported subjective experiences. A sign for example may be a higher or lower temperature ...

s in

multiple sclerosis Multiple sclerosis (MS) is an autoimmune disease resulting in damage to myelinthe insulating covers of nerve cellsin the brain and spinal cord. As a demyelinating disease, MS disrupts the nervous system's ability to Action potential, transmit ...

(MS) and other demyelinating diseases when the body is overheated. This may occur due to hot weather,

exercise Exercise or workout is physical activity that enhances or maintains fitness and overall health. It is performed for various reasons, including weight loss or maintenance, to aid growth and improve strength, develop muscles and the cardio ...

fever Fever or pyrexia in humans is a symptom of an anti-infection defense mechanism that appears with Human body temperature, body temperature exceeding the normal range caused by an increase in the body's temperature Human body temperature#Fever, s ...

, saunas, hot tubs, hot baths, and hot food and drink. Increased

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

slows nerve conduction, but the exact mechanism remains unknown. With an increased body temperature,

nerve impulse An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific Cell (biology), cell rapidly ri ...

s are either blocked or slowed in a damaged nerve. Once the body temperature is normalized, signs and symptoms typically reverse.

Signs and symptoms

Symptoms of Uhthoff's phenomenon occur when exposed to heat, and include: *

fatigue Fatigue is a state of tiredness (which is not sleepiness), exhaustion or loss of energy. It is a signs and symptoms, symptom of any of various diseases; it is not a disease in itself. Fatigue (in the medical sense) is sometimes associated wit ...

pain Pain is a distressing feeling often caused by intense or damaging Stimulus (physiology), stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sense, sensory and emotional experience associated with, or res ...

* concentration difficulties * urinary urgency * worsen of existing optic neuropathy (although optic neuropathy may occur for the first time) * muscle stiffness * dizziness and unsteadiness

Causes

Uhthoff's phenomenon is caused by a raised body temperature. This may be caused by: * hot weather *

* saunas * sun tanning * hot tubs, and hot baths and showers * hot food and drink *

menstruation Menstruation (also known as a period, among other colloquial terms) is the regular discharge of blood and Mucous membrane, mucosal tissue from the endometrium, inner lining of the uterus through the vagina. The menstrual cycle is characterized ...

(which may raise body temperature) * sitting near a radiator

Mechanism

The exact mechanism of Uhthoff's phenomenon is unknown. It causes a decrease in the speed of

action potential An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific Cell (biology), cell rapidly ri ...

s in the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

(CNS). Heat may increase the time when voltage-gated sodium channels are inactivated, which delays further

s. This is worsened by the demyelination caused by MS. Other theories have considered the role of heat shock proteins and changes to

blood flow Hemodynamics American and British English spelling differences#ae and oe, or haemodynamics are the Fluid dynamics, dynamics of blood flow. The circulatory system is controlled by homeostasis, homeostatic mechanisms of autoregulation, just as hydrau ...

. Peripheral nerve studies have shown that even a 0.5 °C increase in body temperature can slow or block the conduction of

s in demyelinated nerves. With greater levels of demyelination, a smaller increase in temperature is needed to slow down the nerve impulse conduction. 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 of mobility aids,

ataxia Ataxia (from Greek α- negative prefix+ -τάξις rder= "lack of order") is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in e ...

, weakness, and

spasticity Spasticity () is a feature of altered skeletal muscle performance with a combination of paralysis, increased tendon reflex activity, and hypertonia. It is also colloquially referred to as an unusual "tightness", stiffness, or "pull" of muscles. ...

. However, exercise has been shown to be helpful in managing MS symptoms, reducing the risk of comorbidities, and promoting overall wellness.

Diagnosis

Diagnosis of Uhthoff's phenomenon is clinical and based on symptoms when it occurs in a person who is already diagnosed with MS. The main differential diagnosis is a more serious worsening of MS symptoms.

Prevention and management

Many patients with MS tend to avoid saunas, warm baths, and other sources of heat. They may wear

ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...

or evaporative cooling clothes, such as vests, neck wraps, armbands, wristbands, and hats. Taking advantage of the cooling properties of

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

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.

Hydrotherapy Hydrotherapy, formerly called hydropathy and also called water cure, is a branch of alternative medicine (particularly naturopathy), occupational therapy, and Physical therapy, physiotherapy, that involves the use of water for pain relief and ...

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

Prognosis

Uhthoff's phenomenon is a temporary problem, and typically completely reverses once body temperature returns to normal. This may take up to 24 hours.

Epidemiology

Uhthoff's phenomenon may affect any person with a demyelinating disease. This is most commonly MS, but it may also occur with neuromyelitis optica spectrum disorder or Guillain-Barré Syndrome. It affects between 60% and 80% of people with MS.

History

Uhthoff's phenomenon was first described by Wilhelm Uhthoff in 1890 as a temporary worsening of vision with exercise in patients with

optic neuritis Optic neuritis (ON) is a debilitating condition that is defined as inflammation of cranial nerve II which results in disruption of the neurologic pathways that allow visual sensory information received by the retina to be able to be transmitted to ...

. Later research revealed the link between neurological signs such as visual loss and increased heat production and Uhthoff's belief that exercise was the etiology of visual loss was replaced by the conclusions of these later researchers stating that heat was the prime etiology.

References

{{Eponymous medical signs for nervous system Symptoms and signs: Nervous system Autoimmune diseases Multiple sclerosis