Myotonia

What is myotonia?

Myotonia is a symptom in which your muscles can’t relax after they contract. For example, you might not be able to let go of someone’s hand after you shake it. Or you may have trouble standing up. There are several types of myotonia. All types happen because of a genetic change. With each type, a different gene is affected.

The genetic changes that cause myotonia can affect other organs throughout your body. Depending on the type of myotonia, this could include your:

• Heart
• Lungs
• Digestive tract
• Brain
• Eyes

Having an unexplained symptom like muscle tightness can be alarming. You may worry about how much worse it’ll get and how it’ll affect your life. The best thing you can do is see a healthcare provider. Given the rarity of myotonia, it may take time to find the correct diagnosis. But your provider can ease your concerns and answer your questions along the way.

Types of myotonia

Healthcare providers classify disorders with myotonia as dystrophic or non-dystrophic. Both of these disorders affect the electrical process that regulates muscle contraction. Dystrophic myotonia also affects the muscle structure itself. “Dystrophy” means “the deterioration of tissue.”

Dystrophic myotonia (DM) is a type of muscular dystrophy that causes muscle weakness and loss (atrophy) over time. Types of DM include:

• Myotonic dystrophy type 1 (DM1) — the most common form
• Myotonic dystrophy type 2 (DM2)

Types of non-dystrophic myotonia include:

• Andersen-Tawil syndrome
• Hyperkalemic periodic paralysis
• Hypokalemic periodic paralysis type 1 and type 2
• Myotonia congenita — the most common form
• Paramyotonia congenita
• Sodium channel myotonia

Non-dystrophic myotonias don’t affect the structure of muscle tissue.

What are the symptoms of myotonia?

The main symptom of myotonia is not being able to relax a muscle after it contracts. Myotonia symptoms can arise in infancy, childhood or adulthood. It depends on the specific type. Other common symptoms include:

• Atypical appearance of your muscles, like an increase (hypertrophy) or decrease (hypotonia) in muscle size
• Fatigue
• Muscle pain
• Muscle weakness
• Muscle stiffness that gets better with activity (warm-up phenomenon)

Each type of dystrophic myotonia has specific symptoms. Examples include:

• Abdominal pain, constipation, diarrhea, acid reflux and bloating
• Atypical facial features (facial dysmorphisms)
• Cataracts that cause blurred vision
• Insulin resistance that causes high blood sugar (hyperglycemia)
• Intellectual disability
• Irregular heartbeat (arrhythmia) or problems with the electrical signals in your heart
• Male pattern baldness (androgenic alopecia)
• Sleep apnea

If you have hyperkalemic periodic paralysis, you may have paralysis (loss of muscle strength) episodes that last from one to four hours. If you have hypokalemic periodic paralysis, you may have muscle weakness at night or early in the morning that lasts from hours to days.

What causes myotonia?

Myotonia happens due to a specific change in one of your genes. More specifically, the gene changes affect the ion channels that are responsible for regulating your muscles’ activity.

Each type of myotonia results from a different gene change. For example, myotonic dystrophy type 1 happens because of an issue with the DMPK gene. Myotonia congenita happens due to an issue with the CLCN1 gene. You may inherit a genetic change from one or both of your biological parents, or you can develop it randomly.

How is myotonia diagnosed?

To start the diagnostic process, your healthcare provider will ask about your symptoms and family health history. They’ll rule out more common conditions that may explain your symptoms, like hypothyroidism, before suggesting tests for myotonia. Tests to diagnose myotonia include:

• Creatine kinase (CK) blood test. Creatine kinase is an enzyme that mainly exists in your muscles. Myotonia typically causes high CK levels.
• Electromyography (EMG). This test evaluates the health and function of your skeletal muscles and the nerves that control them.
• Genetic tests. These tests can often identify genetic changes that cause various forms of myotonia.
• Potassium blood test. Your provider may use this test to check for hyperkalemic periodic paralysis (high potassium) or hypokalemic periodic paralysis (low potassium).
• Short exercise test. During this test, you’ll contract your muscles at measured intervals while a provider monitors how your nerves and muscles respond.

Due to the rarity of myotonia, it may take time before you get a proper diagnosis.

What is the treatment for myotonia?

Treatments for myotonia are specific to each type and the symptoms you have. Together, you and your healthcare provider will tailor a treatment plan to meet your needs. Don’t hesitate to ask questions.

In general, physical therapy may be a part of your treatment. A physical therapist can help you develop an exercise plan that helps avoid known or possible triggers while allowing you to engage in physical activity as much as possible. Occupational therapists can also help you find new ways of doing everyday tasks and may recommend certain adaptive or mobility aids.

Dystrophic myotonia treatments

Treatment of dystrophic myotonias depends on the symptoms. You’ll need regular tests that monitor the health of the organs affected by the type of dystrophic myotonia you have.

The main medication healthcare providers prescribe is mexiletine. It’s actually an antiarrhythmic medication, but it can also help with muscle cramps and stiffness. Mexiletine may also help in some forms of non-dystrophic myotonia.

Non-dystrophic myotonia treatment

Other than medication, treatment of non-dystrophic myotonias may include avoiding triggers, like:

• Avoiding exposure to cold temperatures
• Limiting intense exercise

Periodic paralysis treatment

Treatment of periodic paralysis typically involves managing potassium levels and avoiding triggers. Your provider may recommend avoiding:

• Extended rest after exercise
• High-carbohydrate meals
• Eating meals at irregular times
• Irregular periods of sleep
• Working overnight

If you have hypokalemic periodic paralysis, your provider may recommend eating foods high in potassium, like bananas, beans, dried fruits, mangos and papayas.

If you have hyperkalemic periodic paralysis, you may need to avoid eating foods that have a lot of potassium.

If these measures aren’t enough to manage your symptoms, your provider may prescribe a medication, typically either dichlorphenamide or acetazolamide.

Can I prevent myotonia?

Myotonia happens due to genetic changes, so you can’t do anything to prevent it. If you have a biological family history of myotonia or have it yourself and are planning to have biological children, consider meeting with a genetic counselor. They can go over your risk of having or passing on the condition.

What is the prognosis for someone with myotonia?

If you have myotonia, your prognosis (outlook) can vary depending on several factors, like:

• The type of myotonia you have
• The severity of your symptoms
• How your body responds to treatment
• Your overall health and age

Your healthcare provider will be able to give you a better idea of what to expect given your unique circumstances. But in general:

• Non-dystrophic myotonias typically have a good prognosis, but this can vary based on your symptom severity.
• The prognosis of dystrophic myotonias depends on how severely other body systems are affected. Myotonic dystrophy type 1 and 2 can potentially shorten your lifespan.
• Periodic paralyses can worsen with age and lead to permanent severe muscle issues (myopathy).

When should I see my healthcare provider?

Myotonia is a chronic (long-term) condition. So, you’ll need to see your healthcare provider throughout your life to monitor your symptoms and how well your treatment is working.

It’s important to note that myotonia disorders may affect your reaction to anesthesia. You should contact your provider if you have a surgery planned and notify the anesthesiologist who’ll be taking care of you during surgery.