Drugs blocking Na+ channels (phcnytoin, procainamide, quinine and mexiletine), may reduce myotonia.
Cardiac conduction defects may need a pacemaker.
Identification and treatment of diabetes mellitus is important.
Sedative drugs are to be avoided as patients show an excessive sensitivity.
Genetic counselling should be given.
Cataracts should be dealt with surgically.
This is an autosomal dominant disorder presenting in early middle age. Ptosis is the initial finding with progressive involvement of extraocular muscles until paralysis of all eye movements results. The pupillary reactions are spared. Dysphagia, facial weakness and proximal limb weakness develop later.
Laboratory findings demonstrate a high CK (5 x normal). Muscle biopsy is characteristic with filamentous inclusions in a proportion of muscle fibres. Treatment is supportive, with death eventually from intercurrent infection. Swallowing difficulties may necessitate cricopharyngeal myotomy.
Distinction must be made from myasthenia gravis and mitochondrial myopathy (see later) in which ptosis is a distinctive feature.
LIMB-GIRDLE MUSCULAR DYSTROPHY
This is an autosomal dominant or recessive disorder with onset often delayed to middle age.
Often muscle involvement is asymmetrical and onset is usually in the pelvic girdle muscles. Progression is slow. The disease may arrest in some patients. Muscle enlargement (calves) occurs in a proportion of cases.
Attempts have been made to subdivide on the basis of pelvic or shoulder girdle onset - this has not been convincing. The creatine kinase (CK) is moderately elevated. Cardiac involvement does not occur (ECG normal). EMG studies show non-specific myopathic features. Muscle biopsy confirms myopathy with connective tissue proliferation. Differentiation: This distribution of weakness in proximal muscles may be a feature of chronic spinal muscular atrophy, certain metabolic myopathies, polymyositis and Becker's dystrophy. Investigation is essential to classify correctly as EMG and muscle biopsy will distinguish these disorders.
Treatment: Treatment is symptomatic. Genetic counselling is difficult because of the high frequency of sporadic cases, variable inheritance, and absence of CK elevation in the carrier states.
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