Myotonia

What is myotonia?

Myotonia is a rare condition where your muscles aren’t able to 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.

This disorder can affect other organs throughout your body. Depending on the type of myotonia, the organs that can be affected include your heart, lungs, digestive tract, brain and eyes. Myotonia may be present at birth, or a healthcare provider may diagnose it in mid to late adulthood.

Are there different types of myotonia?

Myotonia disorders are classified 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.

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

• Myotonic dystrophy type 1 (DM1).
• 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.
• Paramyotonia congenita.
• Sodium channel myotonia.

Who might get myotonia?

People who carry a gene mutation that causes the disorders listed above can get myotonia, at any age. It may be present at birth, which healthcare providers call congenital myotonic dystrophy. DM1 may appear between ages 20 to 40, and DM2 may appear during middle age. Healthcare providers may diagnose myotonia congenita between the ages of four and 12, or sometimes in adulthood. Paramyotonia congenita usually appears before age 10.

How common is myotonia?

About 10 people out of 100,000 get myotonic dystrophy. The most common type of myotonia is myotonic dystrophy type 1. About 1 out of every 8,000 people have this condition.

The most common type of non-dystrophic myotonia is myotonia congenita. This affects 1 out of 100,000 people.

What causes myotonia?

Myotonia is usually due to a change (mutation) in your genes. This can be passed on by a family member but may occur without a family history. Your healthcare provider may send you to a genetic counselor to discuss how this disorder will affect other family members, including your children.

What are the symptoms of myotonia?

The main symptom of myotonia is not being able to relax a muscle after it contracts. Depending on the type of myotonia, other symptoms may include:

• Abnormal appearance of your muscle, such as an increase or decrease in muscle size.
• Fatigue.
• Muscle stiffness that gets better with activity, called a warm-up phenomenon. People with paramyotonia congenita and myotonic dystrophy type 2 don’t have this symptom.
• Pain.
• Weakness.

If you have dystrophic myotonia, you may also experience:

• Abnormal facial features (facial dysmorphisms) that may come from bone abnormalities.
• Cataracts that cause blurry vision.
• Diabetes.
• Insulin resistance that causes high blood sugar (hyperglycemia).
• Intellectual disability.
• Irregular heartbeat (arrhythmia) or problems with the electrical signals in your heart.
• Premature hair loss on the front scalp in men.
• Small testes in men.
• Sleep apnea.
• Stomach pain, constipation, diarrhea, reflux and bloating.

If you have hyperkalemic periodic paralysis, you may have paralysis 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.

How is myotonia diagnosed?

To help diagnose myotonia, your healthcare provider will ask about symptoms and family health history. They’ll rule out other conditions, such as hypothyroidism, before suggesting tests for myotonia. Tests to diagnose myotonia include:

• Creatine kinase (CK) test: Your healthcare provider will take a blood sample to test for levels of CK, a type of protein. Myotonia leads to high CK levels.
• Electromyography (EMG): During an electromyogram, your healthcare provider will insert needle electrodes into your muscles. They’ll look for electrical activity when you rest and contract your muscle.
• Genetic tests: Your healthcare provider will take a blood sample to test your genes for changes that may cause myotonia.
• Potassium blood test: Your healthcare provider will take a sample of your blood to check your potassium levels. They may use this test to look 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 and a healthcare provider will monitor your nerve/muscle response.

How is myotonia treated?

Treatments for myotonia are specific to each type:

Dystrophic myotonias

Treatment of dystrophic myotonias depends on the symptoms. You’ll need annual lab work and other tests that monitor the other organs involved in these diseases.

Your healthcare provider may prescribe a medication that blocks the sodium channel that’s on your muscle membrane. This can help with muscle cramps and stiffness. Mexiletine is the primary medication used in this condition, and is used in the dystrophic myotonias and some of the non-dystrophic myotonias.

Non-dystrophic myotonias

Treatment of non-dystrophic myotonias may include:

• Avoiding exposure to cold.
• Limiting heavy exercise.

Periodic paralysis

Treatment of periodic paralysis may include limiting:

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

Hyperkalemic periodic paralysis

Treatment of hyperkalemic periodic paralysis may include:

• Eating a diet high in potassium-rich foods (bananas, beans, dried fruits, mangos, papayas).
• Medication.

Hypokalemic periodic paralysis

Treatment of hypokalemic periodic paralysis may include:

• Eating a diet low in potassium-rich foods.
• Medication.

How can I manage symptoms of myotonia?

To help relieve myotonia symptoms, you can:

• Avoid exposure to cold.
• Avoid strenuous exercise if you have non-dystrophic myotonia.
• Limit carbohydrate-rich foods if you have hypokalemic periodic paralysis.
• Reduce alcohol intake if you have hypokalemic periodic paralysis.
• Reduce your stress levels.
• Use ankle braces and other supportive devices.

Myotonia disorders may affect your reaction to anesthesia. You should contact your healthcare provider if you have a surgery planned and notify the anesthesiologist who’ll be taking care of you during surgery.

How can I reduce my risk of myotonia?

You can’t reduce your risk of myotonia. But you can avoid triggers and manage your symptoms to lead a healthier life.

What can I expect if I have myotonia?

The outlook for myotonia depends on how severe your symptoms are and whether you have other conditions. In particular, periodic paralyses can become worse with age. People with severe cases of dystrophic myotonia may have shortened lifespans.

How do I take care of myself?

Physical therapy can help restore the functioning of your muscles. Physical therapists can help you develop an exercise plan to keep active without triggering your condition. Also, be sure to see your healthcare provider regularly to monitor your symptoms and regularly check heart and breathing function.

A note from Cleveland Clinic

Myotonia occurs when your muscles aren’t able to relax after they contract. Genetic changes usually cause myotonia, which can appear at birth or any age. Symptoms vary depending on the type of myotonia. You can manage symptoms with lifestyle changes, medications, supportive devices and physical therapy.