Mycobacterium avium complex: An unusual cause of hypercalcemia

Abstract

Mycobacterium avium-complex (MAC) is an infectious granulomatous disease which is associated with hypercalcemia especially in immunocompromised patients. We present an unusual case of MAC infection in an immunocompetent patient presenting as hypercalcemia.A 76-year-old immunocompetent male was admitted for hypercalcemia of 12.6 mg/dl found on outpatient evaluation for fatigue. PTH level was low 8 pmol/L, Vitamin D 25hydroxy was 29 ng/ml, 1,25 dihydroxy vitamin D (1,25(OH)2 vitamin D) levels was low at 11 pg/ml, PTH related peptide was 1.1 pmol/L. Hypercalcemia resolved with intravenous hydration and bisphosphonate administration. CT chest identified a nodule with central cavity in the right upper lobe. Pathology from percutaneous biopsy of thenodule demonstrated granulomatous inflammation. AFB culture came positive for MAC. Patient was treated with Azithromycin, Rifabutin and Ethambutol for twelve months.Granulomatous diseases like MAC cause hypercalcemia via activation of macrophages which express extrarenal 1- alpha -hydroxylase. It converts vitamin D to its active form 1,25(OH)2 vitamin D causing its excess, leading to hypercalcemia. Interestingly, in our patient calcium level was elevated with appropriately low PTH but 1,25(OH)2 vitamin D level was also low. There are few reported cases of hypercalcemia in granulomatous disease with normal levels of 1,25(OH)2 vitamin D levels, and our case is the first one to have MAC associated hypercalcemia with low 1,25(OH)2 vitamin D levels, suggesting an alternative mechanism for hypercalcemia in these patients

Keywords

• Hypercalcemia
• Mycobacterium avium complex
• Granulomatous disease
• Immunocompetent