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Letter to the Editor
November 1998

Congenital Adrenal Hyperplasia With Normokalemic Periodic Paralysis

Arch Neurol. 1998;55(11):1487. doi:10.1001/archneur.55.11.1487

Twenty point mutations have been identified in the gene encoding a-subunit of skeletal muscle sodium channel (SCN4A) in patients with hyperkalemic periodic paralysis (HYPP) and myotonic disorders1-4; however, no information on the normokalemic periodic paralysis (NOPP) has been well documented. We encountered an interesting case of congenital adrenal hyperplasia (CAH) accompanying NOPP. Soon after birth, the patient exhibited salt-wasting symptoms. Her mother had noticed abnormalities of the infant's external genitalia since the birth, and she was diagnosed as having CAH due to 21-hydroxylase deficiency by the findings of 46XX chromosomes, the gynecologic laparoscopy, and increased plasma 17a-hydroxyprogesterone and urinary 17-ketosteroid levels. The patient had been treated with glucocorticoid replacement since the diagnosis of CAH, and the dosage had been increased as she grew up. Nevertheless, she began to experience occasional paralytic episodes at 12 years old. The paralysis tended to appear first in the legs, and then spread to her entire body in the course of several days. She remained conscious throughout these episodes. The frequency and duration of these episodes gradually increased, and particularly, the exercise followed by rest provoked severe episodes. Between episodes her muscle strength recovered adequately. These episodes had become more frequent and severe at age 16 years. Results of endocrinologic examinations including thyroid function were not remarkable under the glucocorticoid replacement, anti-acetylcholine receptor antibody was not found, and levels of muscle enzymes and electrolytes during the attack were also normal. The intravenous potassium chloride provocation, which was performed for the diagnosis of periodic paralysis, easily induced such an episode; however, serum potassium concentration (3.7-3.8 mmol/L), electrocardiographic reading, and blood pressure did not change during the episode. The electromyogram measured on the abductor pollicis brevis muscles with 10-Hz repetitive stimulation of the median nerve showed remarkable impairment of amplitude. Her grasping power decreased to 5 kg during attack, compared with 19 kg before testing. Although this paralytic condition was not affected by glucose level, it was immediately remedied by saline injection. The diagnosis of NOPP was hence confirmed.