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Paramyotonia congenita is a rare neuromuscular disorder that causes muscles to be slow to relax after contraction, with symptoms worsened by exercise and cold temperatures. It is caused by a mutation in the SCN4A gene and can be managed by avoiding triggers or medication.
Paramyotonia congenita, also called Eulenburg’s disease or Eulenberg’s paramyotonia congenita, is a rare congenital neuromuscular disorder in which muscles are slow to relax after they contract. In paramyotonia congenita, unlike other neuromuscular disorders, difficulty relaxing muscles, a symptom called myotonia, is paradoxical in the sense that it is made worse rather than improved by prolonged exercise. Eulenburg disease affects fewer than one in 100,000 people.
Patients with Eulenberg disease and other myotonias may have difficulty, for example, letting go of an object they have grasped or getting up from a squatting position. It may take significant effort or time to relax the muscles, and muscle stiffness or weakness can result even after the muscle is no longer contracted. Paramyotonia congenita typically does not cause muscle wasting, but some related conditions do.
Paramyotonia congenita is also characterized by the tendency of cold temperatures to induce myotonia. It most often affects the muscles of the face and upper extremities. Although the paradoxical myotonia associated with Eulenburg disease can lead to muscle weakness, persistent weakness is not a symptom of this particular condition. In addition to exercise and cold weather, some patients find that starvation or eating certain foods, especially those high in potassium, can trigger myotonia.
Paramyotonia congenita is caused by a mutation in the SCN4A gene, which codes for one of the sodium channel proteins responsible for muscle contraction. All people with the mutation will eventually develop the disorder. Most sufferers begin showing symptoms by the age of ten.
Many patients with paramyotonia congenita require no medical treatment. The condition can often be managed by simply avoiding whatever triggers the myotonia and muscle weakness. Some patients may be prescribed medications such as mexiletine or acetazolamide to relieve muscle stiffness.
Eulenburg’s disease has traditionally been considered a separate condition from other sodium channel myotonias and from hyperkalemic periodic paralysis, a genetic disorder in which cold weather causes uncontrollable tremors followed by paralysis. However, it is now being debated whether these various genetic myotonias are distinct conditions or belong to a spectrum of disorders.
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