Myopathy in familial hypokalaemic periodic paralysis independent of paralytic attacks

Case histories and muscle biopsy findings are reported of two members of a family suffering from hypokalaemic periodic paralysis associated with permanent muscular weakness. the first patient aged 9 years, as well as her affected sibs, gives a history of a slight and slowly progressing impairment from early childhood on. At the age of 8 she exhibited slightly reduced muscle strength occasionally in the morning, with a frank paralytic attack only on two occasions. Physical examination revealed slight proximal muscle weakness, predominantly in the legs. Light microscopic examination as well as ultrastructural analysis of the biopsy revealed large vacuoles in many muscle fibres, mostly containing glycogen. the second patient, a man aged 18 years, never experienced a paralytic attack nor any fluctuation in muscle strength. Though his muscular strength was sligthly below expectation, no frank paresis could be detected on examination. the EMG revealed no abnormalities except for slight myopathic changes bilaterally in the adductor magnus. Light microscopic examination of the muscle biopsy showed no pathological changes. Accumulations of glycogen and secondary atrophy and disappearance of muscle fibrils were seen with the electronmicroscope. These observations demonstrate that in this family, myopathic histological changes do not result from paralytic attacks.