Myopathy, Granulovacuolar Lobular, With Electrical Myotonia

The rare combination of muscle weakness with electrical myotonia but without clinical myotonia has been reported in acid maltase deficiency and in centronuclear myopathy. Juguilon et al. (1982) described 3 adult patients with profound selective muscle wasting and weakness, electrical myotonia, and unusual findings on muscle biopsy: vacuoles containing hematoxylinophilic granules, and in 30% of type I fibers, demarcation of the sarcoplasm into lobules due apparently to reorganization of myofibrillar elements. Two of the patients were sibs. The sister, aged 28 years, was well until age 18 years when difficulty climbing stairs and frequent tripping were noted. At age 19, discovery of myotonic discharges on EMG led to the diagnosis of dystrophia myotonica. The brother, aged 30, had similar history and findings. In both, the quadriceps femoris muscles were spared and no cataracts were found on slit-lamp examination.