Pulmonary alveolar microlithiasis

Pulmonary alveolar microlithiasis (PAM) is a rare, chronic lung disease with bilateral intra-alveolar calcium and phosphate deposition throughout the lung parenchyma with predominance to lower and midzone. Although, etiology and pathogenesis of PAM is not fully understood, the mutation in SLC34A2 gene that encodes a sodium-phosphate co-transporter in alveolar type II cells resulting in the accumulation and forming of microliths rich in calcium phosphate (due to impaired clearance) are considered to be the cause of the disease. Chest radiograph and high-resolution CT of thorax are nearly pathognomonic for diagnosing PAM. HRCT demonstrates diffuse micronodules showing slight perilobular predominance resulting in calcification of interlobular septa. Patients with PAM are asymptomatic till development of hypoxemia and cor-pulmonale. No therapy has been proven to be beneficial except lung transplantation.