Myotonia Congenita (Becker & Thomsen Disease)
What is myotonia congenita?
here to be taken to a fact sheet on this condition.
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
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.
Extract from a case study showing treatment
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.