Hypokalemic periodic paralysis in a patient with acquired growth hormone deficiency

Context: Hypokalemic periodic paralysis (HypoPP) is a rare disorder consisting of sudden episodes of muscle weakness with areflexia involving all four limbs, which spontaneously resolve within several hours or days. Primary HypoPP is genetically determined, while secondary acquired HypoPP has been described in association with thyreotoxycosis, hyperaldosteronism, kidney diseases, diuretics and liquorice abuse, gastrointestinal potassium loss, or cysplatinum therapy. Objective: To report a case of HypoPP associated with GH deficiency. Patient: A 33 yr-old man with hypopituitarism and diabetes insipidus secondary to pituitary stalk-localized sarcoidosis, and documented HypoPP episodes. Clinical presentation: Neurologic exam outside HypoPP episodes was normal. Needle electromyography was normal without myotonia or other spontaneous electric activity. Muscle biopsy documented a vacuolar myopathy with tubular aggregates. However, genetic analysis ruled out common mutations of the voltage-gated calcium channel observed in primary HypoPP. Common causes of secondary HypoPP were also ruled out. The patient was diagnosed with severe GH deficiency with modest fasting hyperinsulinemia and insulin resistance and started on GH replacement therapy, an αglucosidase inhibitor (acarbose) and a diet low in simple carbohydrates. Conclusions: GH replacement therapy, acarbose and a diet low in simple carbohydrates resulted in the complete long-term (>2 yr) remission of HypoPP episodes. This is consistent with the hypothesis that the hyperinsulinemia associated to GH deficiency may trigger HypoPP episodes by increasing Na⁺/K⁺ AT-Pase activity and K⁺ transport into the intracellular compartment with subsequent hypokalemia.