Bilateral stony lung: Pulmonary alveolar microlithiasis

A 40-year-old male paddy field worker was referred for exertional shortness of breath and non-productive cough for 4 years. He had been treated for pulmonary tuberculosis twice. Chest radiograph showed extensive bilateral nodular opacities (sandstorm-like) in the middle and lower lobe. Pulmonary function tests revealed a restrictive ventilatory defect. High resolution CT showed widespread nodular infiltration with crazy paving appearance and interrupted black pleura sign. This was confirmed as pulmonary alveolar microlithiasis (PAM) by trans-bronchial lung biopsy, which showed normal respiratory lining epithelium with dilated alveolar spaces containing many calcific bodies, some of which showed concentric calcification. The possibilities of silicosis (due to exposure to husk) and tuberculosis, both of which can mimic PAM clinically and radiologically, made this case a diagnostic challenge.