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 the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality showi ...

s in

multiple sclerosis Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This ...

(MS) and other

demyelinating disease A demyelinating disease is any disease of the nervous system in which the myelin sheath of neurons is damaged. This damage impairs the conduction of signals in the affected nerves. In turn, the reduction in conduction ability causes deficiency i ...

s when the body is overheated. This may occur due to hot weather,

exercise Exercise is a body activity that enhances or maintains physical fitness and overall health and wellness. It is performed for various reasons, to aid growth and improve strength, develop muscles and the cardiovascular system, hone athletic ...

fever Fever, also referred to as pyrexia, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using val ...

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

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

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

nerve impulse An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, c ...

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 describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...

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

* concentration difficulties * urinary urgency * worsen of existing

optic neuropathy Optic neuropathy is damage to the optic nerve from any cause. The optic nerve is a bundle of millions of fibers in the retina that sends visual signals to the brain. Damage and death of these nerve cells, or neurons, leads to characteristic featu ...

(although optic neuropathy may occur for the first time) *

muscle stiffness Delayed onset muscle soreness (DOMS) is the pain and stiffness felt in muscles after unaccustomed or strenuous exercise. The soreness is felt most strongly 24 to 72 hours after the exercise. It is thought to be caused by eccentric (lengthening) e ...

dizziness Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to disequilibrium or a non-specific feeling, such as giddiness or foolishness. Dizziness is a common medical c ...

and unsteadiness

Causes

Uhthoff's phenomenon is caused by a raised

body temperature Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperatur ...

. This may be caused by: * hot weather *

sauna A sauna (, ), or sudatory, is a small room or building designed as a place to experience dry or wet heat sessions, or an establishment with one or more of these facilities. The steam and high heat make the bathers perspire. A thermometer in a ...

s *

sun tanning Sun tanning or tanning is the process whereby skin color is darkened or tanned. It is most often a result of exposure to ultraviolet (UV) radiation from sunlight or from artificial sources, such as a tanning lamp found in indoor tanning be ...

* hot tubs, and hot baths and

shower A shower is a place in which a person bathes under a spray of typically warm or hot water. Indoors, there is a drain in the floor. Most showers have temperature, spray pressure and adjustable showerhead nozzle. The simplest showers have a ...

s * hot food and drink *

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

(which may raise body temperature) * sitting near a

radiator Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in cars, buildings, and electronics. A radiator is always ...

Mechanism

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

action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells ...

s in the

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

(CNS). Heat may increase the time when

voltage-gated sodium channels Sodium channels are integral membrane proteins that form ion channels, conducting sodium ions (Na+) through a cell's membrane. They belong to the superfamily of cation channels and can be classified according to the trigger that opens the chan ...

are inactivated, which delays further

s. This is worsened by the

demyelination A demyelinating disease is any disease of the nervous system in which the myelin sheath of neurons is damaged. This damage impairs the conduction of signals in the affected nerves. In turn, the reduction in conduction ability causes deficiency i ...

caused by MS. Other theories have considered the role of

heat shock protein Heat shock proteins (HSP) are a family of proteins produced by cells in response to exposure to stressful conditions. They were first described in relation to heat shock, but are now known to also be expressed during other stresses including expo ...

s and changes to

blood flow Hemodynamics or haemodynamics are the dynamics of blood flow. The circulatory system is controlled by homeostatic mechanisms of autoregulation, just as hydraulic circuits are controlled by control systems. The hemodynamic response continuously m ...

. 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 is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in eye movements. Ataxia is a clinical manifestation indicating dysfunction of ...

weakness Weakness is a symptom of a number of different conditions. The causes are many and can be divided into conditions that have true or perceived muscle weakness. True muscle weakness is a primary symptom of a variety of skeletal muscle diseases, i ...

, 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

s, warm baths, and other sources of heat. They may wear ice or evaporative cooling clothes, such as

vests A waistcoat ( UK and Commonwealth, or ; colloquially called a weskit), or vest ( US and Canada), is a sleeveless upper-body garment. It is usually worn over a dress shirt and necktie and below a coat as a part of most men's formal wear. I ...

, neck wraps,

armband An armband is a piece of material worn around the arm. They may be worn for pure ornamentation, or to mark the wearer as belonging to group, or as insignia having a certain rank, status, office or role, or being in a particular state or condit ...

s, wristbands, and

hats A hat is a head covering which is worn for various reasons, including protection against weather conditions, ceremonial reasons such as university graduation, religious reasons, safety, or as a fashion accessory. Hats which incorporate mech ...

. Taking advantage of the cooling properties of

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

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 physiotherapy, that involves the use of water for pain relief and treatment. The term ...

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

. This is most commonly MS, but it may also occur with neuromyelitis optica spectrum disorder. 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 describes any condition that causes inflammation of the optic nerve; it may be associated with demyelinating diseases, or infectious or inflammatory processes. It is also known as optic papillitis (when the head of the optic nerv ...

. 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 Etiology (pronounced ; alternatively: aetiology or ætiology) is the study of causation or origination. The word is derived from the Greek (''aitiología'') "giving a reason for" (, ''aitía'', "cause"); and ('' -logía''). More completely, ...

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