Reversible Severe Left Ventricular Dysfunction in an Adolescent With Vitamin D Deficiency-Associated Hypocalcemia and Secondary Hyperparathyroidism: A Case Report

Hypocalcemia is an uncommon but clinically important and potentially reversible metabolic contributor associated with left ventricular (LV) systolic dysfunction and heart failure. Vitamin D deficiency can precipitate hypocalcemia with secondary hyperparathyroidism, and delayed recognition may lead to severe decompensation. We report the case of a 13-year-old female patient with decompensated heart failure and dilated cardiomyopathy with severe LV dysfunction and severe functional mitral and tricuspid regurgitation. Evaluation revealed profound hypocalcemia with low ionized calcium, persistent hypomagnesemia, low 25-hydroxyvitamin D, and markedly elevated parathyroid hormone (PTH), consistent with a multifactorial metabolic derangement including vitamin D deficiency-associated secondary hyperparathyroidism. She was treated with decongestive therapy and guideline-directed heart failure pharmacotherapy alongside targeted correction of calcium, magnesium, and vitamin D deficiency. Serial echocardiography documented progressive recovery of LV systolic function (ejection fraction (EF) 35% at baseline, improving to 40% at one month and 55% at three months), and echocardiography at the one-year follow-up confirmed normal biventricular function (EF 65%) with resolution of valvular regurgitation. This case highlights that systematic screening for calcium, ionized calcium, magnesium, PTH, and vitamin D should be incorporated early in young patients with severe or disproportionate LV dysfunction because identifying metabolic contributors can alter management and prognosis.