Thomsen and Becker Disease: A Patient Guide

Thomsen and Becker diseases are the two primary forms of a rare genetic condition known as myotonia congenita. At its core, this is a disorder of muscle relaxation caused by a malfunction in the electrical “braking” system of your muscle cells ^[1]. While most people’s muscles relax instantly after a contraction, your muscles remain in an excited state for several seconds or even minutes after you try to let go. This results in a persistent feeling of stiffness or “locking up” that can affect everything from your handshake to your ability to walk after sitting for a long period ^[2].

A unique and defining characteristic of this condition is the warm-up phenomenon ^[3]. Unlike many other muscle issues where exercise causes more pain or fatigue, people with myotonia congenita usually find that their stiffness is most intense during their very first movements. As you continue to repeat the activity—such as walking across a room or opening and closing your hand—the stiffness gradually melts away, and your muscles begin to move more fluidly ^[4]. This “warm-up” allows many individuals to remain active throughout their lives, though the severity of the disease and its impact on daily fatigue vary from person to person ^[5].

Doctors distinguish between the two types based on how the condition is inherited. Thomsen disease is the dominant form, often passed directly from one affected parent, and it is typically associated with milder symptoms ^[6]. Becker disease is the recessive form, requiring a gene from both parents, and it tends to be more noticeable. Those with the Becker form often develop hypertrophy—unusually large, powerful-looking muscles—and may experience transient weakness, a brief loss of strength that occurs when they first try to move quickly ^[3][7].

Living with myotonia congenita is largely about management and safety rather than progression or “muscle wasting.” The condition does not typically shorten your lifespan or cause the systemic health problems seen in other muscle dystrophies ^[8]. Symptoms can often be reduced through lifestyle adjustments or medications that help stabilize the electrical signals in your muscles ^[9]. However, the most critical safety measure is ensuring that any surgical team or anesthesiologist knows about your diagnosis, as certain common medications used in surgery (like succinylcholine) can cause dangerous muscle reactions in people with this condition ^[10]. Carry a medical alert card so emergency personnel are aware of this critical precaution. With proper precautions and an understanding of your body’s unique “warm-up” needs, you can navigate daily life with confidence ^[11].