What is Uhthoff Phenomenon?
The Uhthoff phenomenon, also known as Uhthoff’s sign or syndrome, happens when patients with multiple sclerosis (MS) temporarily experience increased neurological problems due to a rise in body temperature. This effect, which often lasts less than a day, was first identified by Wilhelm Uhthoff, a German eye doctor, in 1890. He noticed that physical exercise led to partial or total loss of vision (termed amblyopia) in MS patients. By the 1960s, these symptoms, now known as the Uhthoff phenomenon, were recognized as being triggered by increased body temperature, causing visual problems and other neurological symptoms in MS patients.
In Uhthoff’s original study, physical exercise was thought to be the cause, and the effect of increased body temperature was overlooked. By 1950, a test known as the “hot bath test,” based on these findings, was developed as a way to diagnose MS. But by 1980, more advanced methods like MRI and cerebrospinal fluid analysis replaced the hot bath test as more precise diagnostic tools.
Heat exposure’s temporary increase in neurological problems can affect the physical and mental capabilities of MS patients, making it harder for them to carry out their daily activities. It’s important not to confuse this temporary worsening with an actual relapse or an increase in the severity of MS. Understanding the Uhthoff phenomenon is crucial for recognizing these symptoms and treating them appropriately.
What Causes Uhthoff Phenomenon?
The Uhthoff phenomenon is most commonly seen in people with multiple sclerosis, but it can also occur in other conditions that affect the optic nerves or pathways that carry sensory information, such as neuromyelitis optica. In multiple sclerosis, it’s thought that several factors might cause the Uhthoff phenomenon. These factors can include blockages of channels that let ions pass through, changes in circulation, the effects of calcium in the blood, heat shock proteins (proteins produced in response to stressful conditions), and other substances that are not yet identified.
The most widely accepted explanation for this phenomenon is that it’s caused by a block in conductivity of nerve fibers, especially in areas where the protective layer around the nerve fibers (called myelin) is damaged. This blockage is thought to be sensitive to temperature changes.
Several triggers for the Uhthoff phenomenon have been reported, including the period around menstruation, physical exercise, fever, sunbathing, hot showers, sauna use, psychological stress, and even hot meals or smoking.
Risk Factors and Frequency for Uhthoff Phenomenon
Between 60% and 80% of patients with MS show symptoms of the Uhthoff phenomenon when exposed to heat. In a study, around 52% reported experiencing this phenomenon over a period of 1 to 20 years. Among those MS patients experiencing the Uhthoff phenomenon, 88% had non-visual heat-related symptoms compared to 30% who didn’t show the phenomenon. Approximately 16% of patients fully recovered within 8 weeks. However, if the sign persists beyond 2 months, it could indicate sub-optimal remyelination.
Signs and Symptoms of Uhthoff Phenomenon
Understanding what may cause the worsening of neurological symptoms is important for people with Multiple Sclerosis (MS). Certain factors can trigger this, such as exercise, hot showers or baths, exposure to the sun, menstrual cycles, stress, hot meals, fever, and infections. However, it’s important to note that this worsening of symptoms due to these factors is temporary, typically lasts less than 24 hours, and is often called a “pseudo exacerbation” or “pseudo-relapse”.
If a new neurological issue arises and lasts for at least 24 hours without any obvious fever or infection, this is considered a relapse or exacerbation. This condition is a common trait of relapsing MS. By understanding the patient’s history, it is usually possible to tell the difference between a true relapse and a pseudo-relapse.
During a medical exam, various neurological issues can be found depending on where the demyelination, or damage to the protective cover of the nerves, is located. This could result in a range of symptoms including issues with vision, eye movement disorders, muscular weakness, and abnormal reflexes.
- Exercise
- Having a hot bath or shower
- Exposure to the sun
- Menstrual cycle
- Stress
- Hot meals
- Fever
- Infections
Testing for Uhthoff Phenomenon
Uhthoff phenomenon typically occurs due to areas of damaged nerve insulation, called demyelinating plaques, being stressed by heat. To identify this condition, doctors will need to talk with patients in detail about the situations in which the symptoms came about.
For people already diagnosed with a demyelinating condition who seem to be experiencing a sudden worsening of symptoms (known as a pseudo-relapse), it’s important for doctors to rule out causes like urinary tract infections, upper respiratory tract infections, or metabolic abnormalities. These causes can bring about symptoms that mimic a relapse, so they will often do laboratory tests to check for these.
That’s why it’s important for the doctor to thoroughly check a patient’s medical history, perform a physical examination, and possibly order lab tests. The lab tests will not only rule out metabolic issues, chemical imbalances, and infections but also help to determine whether any new lesions have developed, which could suggest a worsening of the demyelinating condition. They’ll do this mainly with magnetic resonance imaging (MRI). This is a type of scan that can create detailed images of the brain and spine, allowing doctors to spot any areas of lesion or plaque.
If the doctor suspects a new case of a demyelinating or inflammatory condition, they might do a lumbar puncture. This is a procedure where they’ll collect cerebrospinal fluid from your back to test for signs of inflammation or specific antibodies related to demyelinating diseases. The procedure can include various tests that study the fluid composition, check for inflammation markers, and possibly identify specific antibodies or cells associated with demyelination.
Treatment Options for Uhthoff Phenomenon
The crucial step in preventing or handling Uhthoff’s phenomenon, a temporary worsening of symptoms in people with multiple sclerosis (MS) when their body temperature rises, is to be aware of the factors that can increase body temperature and how this can affect a person’s neurological functions and safety. Patients should know how certain activities like hot showers or baths can weaken their arm and leg strength, leading to extreme weakness and putting them at risk of accidents, for instance, drowning. Saunas, direct sunlight when the outside temperature exceeds 30ºC (86ºF), hot water therapies, certain types of heat therapies like short-wave radiotherapy and paraffin application should also be avoided.
To avoid heat sensitivity, patients should exercise in the early morning or late evening when it’s cooler. Fortunately, the effects of Uhthoff’s phenomenon usually go away in a matter of minutes to an hour if the patient rests and is removed from the heat source. To cool down, patients can take cold showers, apply ice packs, use cooling devices, or drink cold beverages. In fact, research has shown that wearing cooling garments can improve motor performance and vision, and reduce feelings of fatigue in people with MS experiencing Uhthoff’s phenomenon.
There’s also a medication, 4-aminopyridine (4-AP), which has been known to reduce the worsening of vision problems when body temperature increases in people with MS. It works by blocking potassium channels, which affects the transmission of nerve signals. A slower-release version of this medication, known as dalfampridine, is FDA-approved to enhance the walking ability of MS patients.
What else can Uhthoff Phenomenon be?
The conditions that might be confused with the topic discussed in the article include:
- Antiphospholipid antibody syndrome
- Behçet disease
- CNS lupus
- CNS lymphoma
- CNS vasculitis
- Copper deficiency
- HIV
- Human T-lymphotropic virus (HTLV)
- Leukodystrophies
- Lyme disease
- Sarcoidosis
- Sjögren syndrome
- Small vessel disease
- Osmotic demyelination syndrome
What to expect with Uhthoff Phenomenon
The outcome of this condition is generally positive, as long as triggers for pseudo-exacerbation, or false worsening of symptoms, are avoided. It’s very important to treat the underlying immune-related disorder to prevent this situation from recurring.
Possible Complications When Diagnosed with Uhthoff Phenomenon
While there are no known complications related to the treatment of this symptom, the use of a medication called dalfampridine does have some reported side effects. These commonly include issues like pain during urination, blood in the urine, frequent urination, and back pain. Some less frequent side effects that some patients have reported include skin crawling sensations, problems with memory, mood issues, difficulty speaking, difficulty swallowing, general tiredness, and inability to control urine and bowel movements.
Known Side Effects of Dalfampridine:
- Pain during urination
- Blood in the urine
- Frequent urination
- Back pain
- Skin crawling sensations (formication)
- Memory problems
- Mood issues
- Difficulty speaking (dysarthria)
- Difficulty swallowing (dysphagia)
- General tiredness (diffuse fatigue)
- Inability to control urine (urinary incontinence)
- Inability to control bowel movements (bowel incontinence)
Preventing Uhthoff Phenomenon
Patients should be educated and reassured about the symptoms and what’s causing them. This includes learning to avoid things that might make the symptoms worse, like taking hot baths or being in environments with a lot of heat. Understanding how symptoms – both new and old – might be connected to a condition where the protective covering of nerve cells is damaged (also known as a demyelinating disease) such as Multiple Sclerosis (MS), can give patients the knowledge they need to tell their doctors if they notice these symptoms. This information can help doctors decide if further tests are needed, for example, to check for new areas of damage or worsening symptoms. This can also signal to the doctor if a patient’s current treatment is not working as well as it should be, and whether the disease might be progressing.
