Myotonia congenita

This is part of Rare diseases.

Diagnosis: Myotonia congenita

Synonyms: Congenital myotonia, Thomsen disease, Becker myotonia

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Date of publication: 2014-10-09
Version: 4.0



The disease

Myotonia congenita is an inherited form of muscle stiffness (myotonia). The disease presents as attacks of muscle stiffness brought on by physical activity immediately after a period of rest. In some cases the stiffness is accompanied by transient periods of muscle weakness. There are two types of myotonia congenita, Thomsen disease and Becker myotonia.

The disorder was first described in 1876 by the Danish physician Julius Thomsen who was affected by the condition himself, as were more than twenty of his relatives over several generations. In 1971, the German physician Peter Emil Becker described a variant with a different inheritance pattern, which frequently gives more severe symptoms.


International medical literature indicates that myotonia congenita affects approximately 6 individuals per 100,000 population. This means that there are between 500 and 600 individuals with myotonia congenita in Sweden. However, many of them have not yet received an accurate diagnosis. Becker myotonia is about twice as common as Thomsen disease.


Both variants of myotonia congenita are caused by a mutation in gene CLCN1, a gene which controls the production of (codes for) one of the proteins making up the muscle’s chloride channel. This gene is located on chromosome 7 (7q35). The chloride channel can be described as a pore consisting of two matching sub-units in the membranes of muscle fibres. This pore normally opens to allow chloride ions to pass into the cell after a muscle contraction. It is essential that chloride ions flow rapidly through the pore in order to restore and maintain the difference in electric charge between the outside and inside of the cell. If the functioning of the chloride channel is impaired the muscle is not able to relax, leading to stiffness. More than 100 mutations in gene CLCN1 have been identified, associated with different inheritance patterns and varying degrees of severity.


The inheritance pattern of Thomsen disease is autosomal dominant, while Becker myotonia is an autosomal recessive disorder.

An autosomal dominant pattern of inheritance means that one of the parents has the disease, and so has one normal gene and one mutated gene. Sons and daughters of this parent have a 50 per cent risk of inheriting the disease. Children who do not inherit the mutated gene do not have the disease and do not pass it down.

Figure: Autosomal dominant inheritance

An autosomal recessive inheritance pattern means that both parents are healthy carriers of a mutated gene. In each pregnancy with the same parents there is a 25 per cent risk that the child will inherit double copies of the mutated gene (one from each parent). In this case the child will have the disease. In 50 per cent of cases the child inherits only one mutated gene (from one parent only) and like both parents, will be a healthy carrier of the mutated gene. In 25 per cent of cases the child will not have the disease and will not be a carrier of the mutated gene.

Figure: Autosomal recessive inheritance

A person with an inherited autosomal recessive disease has two mutated genes. If this person has a child with a person who is not a carrier of the mutated gene, all the children will inherit the mutated gene but they will not have the disorder. If a person with an inherited autosomal recessive disease has children with a healthy carrier of the mutated gene (who has one mutated gene) there is a 50 per cent risk of the child having the disorder, and a 50 per cent risk of the child being a healthy carrier of the mutated gene.


Symptoms of Thomsen disease commonly manifest in infancy, and in both forms of myotonia congenita onset is before the age of 15. However, there are cases where symptoms do not manifest until the individual is in his or her thirties. The predominant symptom is muscle stiffness triggered by strenuous exercise immediately after a period of rest. All voluntarily-controlled musculature can become stiff, even that which controls the movements of the eyes, face and tongue. The stiffness is relieved if the individual continues physical activity. This is often called “warming up.” In many cases stiffness is accompanied by transient muscle weakness. Sudden loud noises or other unexpected stimuli may trigger severe muscle stiffness and weakness, sometimes even causing the individual to fall down. Muscle stiffness may also be triggered, or aggravated, by exposure to cold, stress, fasting, and fatigue. Muscle strength is usually normal between attacks, although some individuals may experience mild weakness of the neck, the lower arms, and the hands. Myotonic stiffness causes the muscles to tense even when the individual is at rest, and as a result the individual may have larger than normal muscles, particularly in the calves, thighs and buttocks. Muscle pain is common. The symptoms of Thomsen disease and Becker myotonia differ slightly.

Thomsen disease presents early (at between one and two years of age) and is not progressive. The symptoms affect all muscles including the face, tongue, and pharynx. The degree of muscle stiffness varies, even within the same family, and some people with the mutation are symptom-free throughout life.

Becker myotonia has a later onset (between the ages of 5 and 15), muscle stiffness is more severe, and it may progress slowly until around the age of thirty when it stabilises or becomes less pronounced. The stiffness is most severe in the legs, but may gradually spread to the arms and face. Unlike Thomsen disease, there is often mild muscle atrophy of the arms.

Muscle stiffness may increase as a result of certain medical treatments, such as some asthma medications (beta-agonists), medications used to treat heart problems and high blood pressure (beta-blockers), diuretics, and muscle relaxants sometimes used in surgical procedures.

For reasons as yet unclear, men often have more severe symptoms than women. The severity of the disease often varies greatly within the same family. Women commonly experience a temporary worsening of muscle stiffness during pregnancy. Muscle stiffness is also worse in cases where the metabolism is impaired (hypothyroidism).


The diagnosis is based on typical symptoms and by confirming muscle stiffness in physical activity after rest. Muscle weakness which follows a muscle contraction (myotonic muscular contraction) can often be stimulated by a light blow to a muscle with a reflex hammer.

An electromyography (EMG), which measures electrical activity in the musculature, will show typical muscle stiffness without indicating signs of any other muscle disease. Special tests where the nerve is electrically stimulated and the muscle response measured (decremental response or exercise test) can often establish the presence of changes typical of myotonia congenita.

A muscle biopsy, a procedure in which a piece of muscle tissue is removed and examined microscopically, is often performed. In myotonia congenita, the muscle biopsy is usually normal or displays only minor abnormalities.

Tests for the muscle enzyme creatine kinase (CK) can sometimes reveal elevated levels (two to four times above normal values).

DNA analyses confirm a diagnosis in more than 95 per cent of cases. At the time of diagnosis it is important that the family is offered genetic counselling. Carrier and prenatal diagnosis, as well as pre-implantation genetic diagnosis (PGD) in association with IVF (in vitro fertilization), are available to families where the mutation is known.


There is currently no cure for the disease. It is important to learn what triggers attacks of muscle stiffness. Physical activities should preferably be carried out at an even pace without long breaks, and lengthy periods without food should be avoided. As myotonic stiffness is relieved by repetitive muscular activity, it is possible to prepare for more strenuous activities by carefully warming up the muscles. Most individuals with the disorder learn to manage muscle stiffness, for example by avoiding exposure to cold. Since stress can induce myotonic reactions, it is important to avoid stressful situations. There should be contact with a physiotherapist for both general and specific advice about physical exercise.

Certain medications can reduce muscle stiffness, and many individuals with myotonia congenita use these drugs regularly or periodically. The most effective one is mexiletine. In Sweden the use of this drug requires authorization by the Swedish Medical Products Agency.

Under general anaesthesia, some medications used to relax muscles (depolarizing muscle relaxants, suxamethonium for example) may trigger severe myotonia and cause breathing difficulties. It is therefore important that the anaesthetist is informed about the disorder well before a planned surgical intervention.

Other medications which should be avoided if possible are adreneline, beta-adrenergic agonists, propranolol and colchicine as these can exacerbate muscle stiffness.

It is important for children with the disease to be in regular contact with a paediatric neurologist as they are growing up. Habilitation is available for those children who need it, and is planned according to their needs in collaboration with those close to the child. A habilitation team includes professionals with special expertise in how disability affects everyday life, health and development. Help is available within the medical, educational, psychological, social and technical fields. Habilitation may include assessments, treatment, assistance with choice of aids, information about disabilities and counselling. Information is also given about support offered by public services as well as advice on the way accommodation and other environments can be adapted to the child’s needs.

It is important to provide psychological support to people with the condition and their relatives. Children and young people should be offered continuous support tailored to their age and maturity, and this should continue in adulthood.

It is helpful to be well-informed about the disorder when making choices about education and what games and sports to participate in. When deciding on a suitable career, it is important to avoid jobs requiring great physical exertion particularly outdoors in cold weather. Career guidance for people whose capacity to work is limited by disability is offered by the Swedish Public Employment Service.

Adults with myotonia congenita should be in contact with a neurologist.

Practical advice


National and regional resources in Sweden

Neurologists and paediatric neurologists at regional and county hospitals can confirm the diagnosis. At university hospitals in Gothenburg, Linköping, Örebro and Stockholm there are units which specialize in neuromuscular diagnostics.

Resource personnel

Associate Professor Christopher Lindberg, Neuromuscular Centre, Sahlgrenska University Hospital/Sahlgrenska, SE-413 45 Gothenburg, Sweden. Tel: +46 31 342 10 00, email: christopher.lindberg@vgregion.se.

Senior Physician Björn Lindvall, Muscle Centre, Örebro University Hospital, SE-701 85 Örebro, Sweden. Tel: +46 19 602 10 00, email: bjorn.lindvall@orebroll.se.

Associate Professor Göran Solders, Neurology Clinic, Karolinska University Hospital, SE-141 86 Stockholm, Sweden. Tel: +46 8 585 800 00, email: goran.solders@karolinska.se.

Professor Már Tulinius, The Queen Silvia Children’s Hospital, SE-416 85 Gothenburg, Sweden. Tel: +46 31 343 40 00.

Courses, exchanges of experience, recreation


Organizations for the disabled/patient associations etc.

Neuro Sweden, Box 49084, St Eriksgatan 44, SE-100 28 Stockholm, Sweden. Tel: +46 8 677 70 10, fax: +46 8 24 13 15, email: info@neuroforbundet.se, www.neuroforbundet.se.

Courses, exchanges of experience for personnel


Research and development


Information material

Short summaries of all the database texts are available as leaflets, in Swedish only. They can be printed out or ordered by selecting the Swedish version, and then clicking on the leaflet icon which will appear under, “Mer hos oss” in the column on the right-hand side.


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Colding-Jorgensen E, Duno M, Schwartz M, Vissing J. Decrement of compound muscle action potential is related to mutation type in myotonia congenita. Muscle Nerve 2003; 27: 449-455.

Conravey A, Santana-Gould L. Myotonia congenita and myotonic dystrophy: surveillance and management. Curr Treat Options Neurol 2010; 12: 16-28.

Duno M, Coling-Jorgensen E, Grunnet M, Jespesen T, Vissing J, Schwartz M. Difference in allelic expression of the CLCN1 gene and the possible influenze on the myotonia congenita phenotype. Eur J Hum Genet 2004; 12: 738-743.

Farbu E, Softeland E, Bindoff LA. Anaesthetic complications associated with myotonia congenita: case study and comparison with other myotonic disorders. Acta Anaesthesiol Scand 2003; 47: 630-634.

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Horga A, Raja Rayan DL, Matthews E, Sud R, Fialho D, Durran SC et al. Prevalence study of genetically defined skeletal muscle channelopathies in England. Neurology 2013; 80:1472-1475.

Jurkat-Rott K, Lerche H, Weber Y, Lehmann-Horn F. Hereditary channelopathies in neurology. Adv Exp Med Biol 2010; 686: 305-334.

Koty PP, Pegoraro E, Hobson G, Marks HG, Turel A, Flagler D et al. Myotonia and the muscle chloride channel: Dominant mutations show variable penetrance and founder effect. Neurology 1996; 47: 963-968.

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Lehmann-Horn F, Jurkat-Rott K, Rüdel R; Ulm Muscle Centre.
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Sun C, Tranebjaerg L, Torbergsen T, Holmgren G, Van Ghelue M. Spectrum of CLCN1 mutations in patients with myotonia congenita in Northern Scandinavia. Eur J Hum Genet 2001; 12: 903-909.

Tan SV, Matthews E, Barber M, Burge JA, Rajakulendran S, Fialho D et al. Refined exercise testing can aid DNA-based diagnosis in muscle channelopathies. Ann Neurol 2011; 69: 328-340.

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Thomsen J. Tonische Krämpfe in willkürlich beweglichen Muskeln in Folge von ererbter psychischer Disposition. (Ataxia muscularis?). Archiv für Psychiatrie und Nervenkrankenheiten 1876; 6: 702-718.

Trip J, Drost G, van Engelen BG, Faber CG. Drug treatment for myotonia. Cochrane Database Syst Rev 2006; (1): CD004762.

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Database references

OMIM (Online Mendelian Inheritance in Man)
Search: myotonia congenita, thomsen disease, becker myotonia

GeneReviews (University of Washington)
www.genetests.org (select GeneReviews)
Search: myotonia congenita

Document information

The Swedish Information Centre for Rare Diseases produced and edited this information material.

The medical expert who wrote the draft of this information material is Associate Professor Göran Solders, Karolinska University Hospital, Stockholm, Sweden.

The relevant organizations for the disabled/patient associations have been given the opportunity to comment on the content of the text.

An expert group on rare diseases, affiliated with the University of Gothenburg, approved the material prior to publication.

Date of publication: 2014-10-09
Version: 4.0
Date of publication of the Swedish version: 2014-03-25

For enquiries contact The Swedish Information Centre for Rare Diseases, The Sahlgrenska Academy at the University of Gothenburg, Box 422, SE-405 30 Gothenburg, Sweden. Tel: +46 31 786 55 90, email: ovanligadiagnoser@gu.se.


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