Autosomal Dominant Calpainopathy in a Diabetic Patient Complicated by Functional Gitelman Syndrome

Adult-onset Gitelman syndrome with calpainopathy is a rare clinical condition in patients with diabetes mellitus. We present the case of a 52-year-old male diabetic patient who presented with muscle weakness and fatigue. On evaluation, he had reduced power in the thigh and pelvic girdle muscles. Laboratory tests revealed hypokalemia, hypomagnesemia, metabolic alkalosis, kaliuresis, and hypocalciuria, which led to the diagnosis of Gitelman syndrome. Electromyography revealed a myopathic pattern with polyphasic motor unit action potentials of a short duration. Genetic analysis revealed a heterozygous mutation in CAPN3, suggestive of autosomal dominant calpainopathy or limb girdle muscular dystrophy. He was administered intravenous potassium and magnesium supplements, followed by oral potassium chloride, magnesium oxide, and potassium-sparing diuretics. The patient had improved muscle strength on follow-up, with resolution of the electrolyte abnormalities. This case report highlights this rare clinical entity, its variable clinical manifestations, and the pathophysiological mechanisms involved in electrolyte abnormalities.