Pulmonary Alveolar Microlithiasis: A Disorder of Pulmonary Phosphate Homeostasis

Pulmonary alveolar microlithiasis is an ultrarare autosomal recessive lung disease caused by loss of a key pulmonary epithelial sodium phosphate cotransporter resulting in elevation of luminal phosphate and accumulation of calcium phosphate crystals in alveolar spaces. The disease is often discovered incidentally on routine chest films in asymptomatic individuals or through screening of families with a known history of pulmonary alveolar microlithiasis (PAM) and tends to progress slowly, often culminating in respiratory failure in late middle age. Current management is limited to supportive measures, with lung transplantation in end stage disease. Recent advances in the pathogenesis of PAM have suggested therapeutic approaches.