A case of hypercalcemia secondary to hot tub lung

Hypersensitivity pneumonitis (HP) is a diffuse granulomatous lung disease resulting from inhalation of an antigen to which an individual has been previously sensitized. Hot tub lung is an increasingly common form of HP associated with inhalation of water aerosols containing Mycobacterium avium complex organisms that contaminate hot tub water. Granulomatous lung disorders, most classically sarcoidosis, have been associated with unregulated 1-α-hydroxylase expression by macrophages present in the granulomas, causing conversion of 25-OH-vitamin D to the active form of vitamin D, 1,25(OH)2 vitamin D, and, thus, hypercalcemia. To our knowledge, this is the first confirmed case of hypercalcemia secondary to elevated 1,25(OH)2 vitamin D levels associated with HP.