Autosomal-dominant Thomsen Congenital Myotonia

The first thorough description of myotonia congenita dates bask to 1876, when German physician Julius Thomsen, published a manuscript on a muscle ailment afflicting various members of his family including himself.

First symptoms appear in early infancy (between first and second year of age), but due to mild clinical picture this diseases in frequently diagnosed later in childhood. The child appears clumsy and has difficulties in initiating movements after periods of rest. Muscles are stiff, especially in legs (for example after trying to get up after longer sitting). Patients as well experience difficulties when climbing to stairs. Due to longer period needed for muscle relaxation, inability of eye opening (after crying and sneezing) is observed. Muscle hypertrophy is not characteristic for this type of disease.

Disease can vary in severity from mild to moderate with severe cases being rare. Life expectancy is not shortened. There is no progression of the symptoms and most affected subjects learn to live with condition and avoid unpleasant attacks of muscle stiffness.

In patients with Thomsen disease involvement of central nervous systems well as other organs has not been observed.

Thomsen disease is characterized by pronounced intrafamilial variability, which means that different family members of the same family can have different symptoms or severity of disease. In some family members disease can be severe while in others appears asymptomatic and is observed only after electromyographic testing.

 Autosomal Recessive Becker Congenital Myotonia

The eponym for this disorder is in honor of German physician Peter Emil Becker who after long-term follow up of the patients with congenital myotonia observed that among Thomsen congenital myotonia another very similar entity, different by its type of inheritance and severity of clinical symptoms exists.

First symptoms in patients with Becker congenital myotonia appear later comparing to the ones in Thomsen disease, usually between ages of 4 to 12 years. In these patients myotonia is generalized (all muscles are affected). Due to chronic increased skeletal muscle activity, usually muscle hypertrophy and body “builder-like appearance” is found. Patients with Becker congenital myotonia experience episodes of muscle weakness, especially in hands and fists, most frequently upon initiating movement after long periods of rest. As well, after time a permanent muscle weakness can be appear. Even though myotonia doesn’t cause pain in most patients, it is known that some people complain on painful muscle jerks and myalgia, especially after intensive physical activity.  This type of weakness is almost never observed in patients with Thomsen disease.

 Paramyotonia Congenita (Congenital Paramyotonia)

This disease has been firstly described by Eulenburg in 1886. It is characterized by periods muscle stiffness and paralysis that are worsened by cold and longer and intensive physical activity.

Disease is inherited in autosomal-dominant fashion and it is caused by mutations of SCNA4 gene responsible for sodium channel function in skeletal muscles. Symptoms usually appear in the first decade of life.  Facial muscles, tongue and hands are most frequently affected, while rarely less severe symptoms can be observed in lower extremities. Myotonia in this muscles lasts for couple of seconds on minutes, while muscle weakness can persist for hours or even days. Comparing to other types of myotonias, muscle stiffness is worsened by repetitive muscle movements. Muscle hypertyrophy is found in about 30% of the patients.