Rare disease causes unusual amount of leg cramps

Q: I am a 79-year-old woman, and I have in the past had night cramps that went away when I stamped my foot. When it got worse, including a burning sensation, a muscle relaxant helped. It's back again, and my neurologist says I have cramp-fasciculation syndrome. What is that?

A: Cramp-fasciculation syndrome, also known as CFS, is a rare condition that was first identified 30 years ago. It's a nerve disorder in which muscle fibers contract spontaneously, which causes spasms, twitches or cramps. These contractions commonly occur in the thigh and calf muscles, and they are the result of abnormal and ongoing surges of nerve activity.

Symptoms include the cramping, pain and burning that you describe, the sensation of constant muscle contraction, and also sometimes numbness, prickling or tingling in the affected area. Some people experience muscle stiffness, reflexes that are overly responsive and fatigue and anxiety. Although the symptoms of CFS typically affect the legs, it can occur in other parts of the body, such as the muscles of the arms and chest.

The condition can appear independently of any other type of illness or nerve disease or disorder, and it can be present in someone who is otherwise healthy. Because the disease is rare, few studies have been done. These studies included small sample sizes, which has made it a challenge to draw conclusions about causes and risk factors. There does appear to be a genetic link to something known as ion channel diseases. These are disorders in which a certain function of the cell membrane, which helps the regulation of electrical signals throughout the body, isn't working properly.

However, many cases of CFS are idiopathic, which means they occur without a known cause. Patients report that physical activity often triggers the symptoms of cramp-fasciculation syndrome. There is some evidence that the spasms, twitching and cramping of CFS can be relieved with stretching exercises, and also with massage. The severity of the condition can range from perceptible muscle movement that causes no pain to symptoms severe enough to interfere with daily life.

There are no specific diagnostic tests for cramp-fasciculation syndrome. The condition is identified by the presence of its unique and characteristic symptoms. This includes a history of the same sensations and muscle cramping that you have been experiencing. Because serious neuromuscular disorders, such as amyotrophic lateral sclerosis, or ALS, can share some of the symptoms as cramp-fasciculation syndrome, it's important for them to be ruled out.

Again, this is a rare disease, so there is limited information about treatment. In some cases, the condition resolves on its own. Medications can include anticonvulsants, which reduce the hyper-excitability of nerves by decreasing nerve impulses, and drugs that treat neuropathic pain. Corticosteroids, such as prednisone, have also been used with success. In order to keep track of pain levels and monitor muscular control over time, physical therapy may be recommended.

The drugs used to treat the condition can cause side effects, and some patients have found that gradually working up to the recommended dosage helped them to tolerate the medications.

• Dr. Eve Glazier is an internist and associate professor of medicine at UCLA Health. Dr. Elizabeth Ko is an internist and assistant professor of medicine at UCLA Health. Send your questions to askthedoctors@mednet.ucla.edu.