A rare case of unilateral adrenal hyperplasia accompanied by hypokalaemic periodic paralysis caused by a novel dominant mutation in CACNA1S: features and prognosis after adrenalectomy

BACKGROUND Acute hypokalaemic paralysis is characterised by acute flaccid muscle weakness and has a complex aetiological spectrum. Herein we report, for the first time, a case of unilateral adrenal hyperplasia accompanied by hypokalaemic periodic paralysis type I resulting from a novel dominant mutation in CACNA1S. We present the clinical features and prognosis after adrenalectomy in this case. CASE PRESENTATION A 43-year-old Han Chinese male presented with severe hypokalaemic paralysis that remitted after taking oral potassium. The patient had suffered from periodic attacks of hypokalaemic paralysis for more than 20 years. A computed tomography (CT) scan of the abdomen showed a nodular mass on the left adrenal gland, although laboratory examination revealed the patient had not developed primary aldosteronism. The patient underwent a left adrenalectomy 4 days after admission, and the pathological examination further confirmed a 1.1 cm benign nodule at the periphery of the adrenal gland. Three months after the adrenalectomy, a paralytic attack recurred and the patient asked for assistance from the Department of Medical Genetics. His family history showed that two uncles, one brother, and a nephew also had a history of periodic paralysis, although their symptoms were milder. The patient's CACNA1S and SCN4A genes were sequenced, and a novel missense mutation, c.1582C > T (p.Arg528Cys), in CACNA1S was detected. Detection of the mutation in five adult male family members, including three with periodic paralysis and two with no history of the disease, indicated that this mutation caused hypokalaemic periodic paralysis type I in his family. Follow-up 2 years after adrenalectomy showed that the serum potassium concentration was increased between paralyses and the number and severity of paralytic attacks were significantly decreased. CONCLUSION We identified a novel dominant mutation, c.1582C > T (p.Arg528Cys), in CACNA1S that causes hypokalaemic periodic paralysis. The therapeutic effect of adrenalectomy indicated that unilateral adrenal hyperplasia might make paralytic attacks more serious and more frequent by decreasing serum potassium. This finding suggests that the surgical removal of hyperplastic tissues might relieve the symptoms of patients with severe hypokalaemic paralysis caused by other incurable diseases, even if the adrenal lesion does not cause primary aldosteronism.