Hypokalemic periodic paralysis

THE CLINICAL SYNDROME of periodic paralysis is typically described as consisting of temporary weakness of skeletal muscle in individuals who are normal between attacks. Many conditions can produce periodic weakness. These include aldosteronism, hyperthyroidism, myophosphorylase deficiency, myasthenia gravis, hysteria, paramyotonia congenita, acute intermittent porphyria, idiopathic myoglobinuria, gastrointestinal and renal disease associated with excessive loss of potassium, and exposure to exogenous toxins. When these conditions have been excluded, there still remains a poorly understood group that is identified by changes in serum potassium during an attack. Many syndrome names are given to each group, but essentially they consist of periodic paralysis with low, high, or normal potassium in the serum during an attack. Despite the clinical requirements that the patient be normal between attacks, permanent interictal weakness has been reported in all three groups.l-21 At least 33 instances of permanent paresis have been reported in patients with assumed or proved hypokalemia during an attack (Table 1). Although nine of these cases were reported before Biemond and Daniels ( 1934)IO discovered that potassium dropped during an attack, Singer and Goodbody2* suggested treating t h i s condition with potassium salts in 1901. Usually the permanent weakness occurred late in the disease; in only one case reported did it definitely occur before the age of 14 years. The purpose of this paper is to present the clinical course and muscle biopsy and electromyographic findings in two children who had the syndrome of hypokalemic periodic paralysis and who developed permanent proximal weakness at the ages of 9 and 12 years. Although most biopsy reports describe vacuolization of muscle fibers, and electromyography has, on occasion, demonstrated neurogenic findings, these were not present in our cases.