Myotonia, which is the main symptom in these cases and concerns skeletal muscles rather than heart and gastrointestinal muscles, affects the ability of the muscle to relax after movement. The myotonic crisis is usually transient and essentially results in an inability to relax and lift from the sitting position. It lasts from a few seconds to minutes and can cause uncomfortable feelings to complete incompetence. It can be activated after exposure to cold or intense noises, affecting, depending on the type, feet, face, arms, hips, shoulders, eyelids and speech ability. They are inherited autosomally either dominantly or in a recessive pattern. Many are cngenital, but depending on type and severity, the symptoms start by adolescence or adulthood.
- Congenital Myotonia
It is hereditary that is manifested by birth and does not affect life expectancy and development of the individual. It is distinguished in two types: A. Thomsen’s disease, B. Becker disease. Their differences lie in the severity of the clinical condition and the pattern of inheritance.
- Thomsen’s Disease: it is autosomal dominant, with milder symptoms than Becker, which begin earlier, early in childhood or even at birth. In very mild cases, symptoms are not observed for many years.
- Becker Disease: It is an autosomal recessive with symptoms onset from the end of childhood or the beginning of puberty, but depending on the severity, symptoms may also occur at the beginning of childhood. Usually symptoms are more severe for a few years after diagnosis and the condition stabilizes during the second decade.
In both cases there is myotonia mainly in the legs, which makes walking difficult and causes falls. Hands, shoulders and head are often affected and problems arise in chewing, handles and eye blink. In rare cases of Becker after myotonic crisis, there is weakness for a few seconds to hours, depending on the strength of the crisis. In addition, in both cases, the myotonic crisis can be overcome by repeated use of the affected muscle. Stiffness will worsen after the first contractures and with repetitive moves, it will recede, allowing normal muscle function. This process allows intense moves and sport, especially those that require strength rather than speed. Muscles are hypertrophic), mainly of legs and buttocks, but also in the arms, shoulders, back, especially in Becker disease.
- Congenital Paramyotonia
It is autosomal dominant, stable and non-life-threatening disease. Symptoms are distinguished from birth or at the beginning of childhood, with generalized myotonic rigidity, mainly in the hands, face and neck. It is activated or gets worse after intense physical exercises or even after exposure to low temperatures (which improves after exposure to high temperature). It is often accompanied by weakness of the affected area, which can last from a few minutes to hours. Here the rigidity does not improve with repeated movements of affected muscle. On the contrary it gets worse, characterized as paradoxical myotonia.
- Schwartz-Jampel Syndrome
This is the most serious case, very rare and inherited in an autosomal recessive pattern. Symptoms start from birth or shortly after, and vary depending on the case. In particular, stiffness occurs in face and thighs, often causing falls, speech difficulties and other skeletal anomalies in the face. As in congenital myotonia, repetitive moves of affected muscle can relieve stiffness. Multiple skeletal abnormalities cause developmental problems, hypertrophic thighs, atrophic shoulders and hips, muscle twists (intense and severe moves) and in some cases mental retardation.
- Clinical exams to test myotonic responses to various stimuli (eg low temperatures).
- Laboratory blood tests.
- Genetic test.
- Muscle biopsy.
There is no cure, but without medication, most people live normally. If myotonia worsens, medication such as mexiletine, quinine, procanimide, tegretol, phenytoin, unfortunately with severe side effects. When someone is aware of the factors that can trigger a myotonic crisis, avoids them and does not show symptoms and thus avoids medication.
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- Dunø ,E. Colding-Jørgensen, Myotonia Congenita, https://www.ncbi.nlm.nih.gov/books/NBK1355/?report=readerMuscular Dystrophy Canada, Myotonic Non Dystrophic, http://muscle.ca/wp-content/uploads/2012/11/431E_Myotonic_Non_Dystrophic_2007.pdf
- Muscular Dystrophy Association, About Neuromuscular Diseases, June 08, 2017, https://www.mda.org/disease/
- Muscular Dystrophy Canada, Myotonia Congenita, Muscular Dystrophy Canada, http://www.muscle.ca/about-muscular-dystrophy/types-of-neuromuscular-disorders/myotonia-congenita/, August 30, 2017.
- NORD (National Organization for Rare Disorders), rare diseases, Myosin storage Myopathy, https://rarediseases.info.nih.gov/diseases/