Myotonia Congenita (Becker & Thomsen Disease)

What is myotonia congenita?

Click here to be taken to a fact sheet on this condition.

Treatment options:

The treatment of Thomsen and Becker types myotonia congenita is directed toward the specific symptoms that are apparent in each individual. Such treatment may require the coordinated efforts of a team of medical professionals, such as pediatricians; specialists who diagnose and treat disorders of the skeleton, joints, muscles, and related tissues (orthopedists); physical therapists; and/or other health care professionals.

Specific therapies for the treatment of Thomsen and Becker diseases are symptomatic and supportive. In some cases, certain medications may be prescribed to help diminish muscle stiffness and other symptoms resulting from myotonia. In addition, special exercises may be advised to help alleviate myotonic symptoms, since associated muscle rigidity may improve with proper movement and exercise of involved muscle groups.

As discussed earlier, two sisters with Becker type myotonia congenita demonstrated susceptibility to a malignant hyperthermia-like response. Although the implications of this finding are not fully understood, this potential risk must be taken into consideration by surgeons, anesthesiologists, dentists, and other health care workers when making decisions concerning surgery, the use of particular anesthetics, and the administration of certain medications.

Early intervention is important to ensure that affected children reach their potential. Special services that may be beneficial include special social support, physical therapy, and/or other medical, social, and/or vocational services.

Sourced from accessed 24/12/2015

Extract from a case study showing treatment options:

Many patients with myotonia can cope with their symptoms without the use of medications. As described in the present case, however, patients with recessive MC can experience severe myotonia, which hinders their daily activities.

Muscle stiffness responds well to drugs that reduce the associated hyperexcitability of the sarcolemma by interfering with sodium channels located on it. These drugs theoretically reduce spontaneous discharges of electrical myotonia by decreasing the number of available sodium channels, but they have no known effects on chloride channels. One such drug is mexiletine, which is able to reduce myotonia with doses of 200 mg two or three times a day. Possible adverse side effects of mexiletine include epigastric discomfort, nausea, tremor, anxiety and headaches, and in patients with recessive MC, there is a possibility of an increase in muscle weakness. Before prescribing mexiletine, an electrocardiogram must be performed to eliminate contraindications such as cardiac arrhythmias, coronary heart disease or cardiomyopathy.

Phenytoin 200-300 mg per day can also be used to treat myotonia. Care must be taken with the use of depolarizing muscle relaxants such as suxamethonium during anesthesia, because they can cause adverse events such as life-threatening muscle spasms and ventilation difficulties following a preoperative injection.

Particular care should also be taken with injections of adrenaline or selective beta-adrenergic agonists, because they aggravate myotonia.

Sourced from accessed 24/12/2015