Diffuse Pulmonary Ossification (DPO) in the Setting of Firefighter Occupation.

A 76-year-old man with a past occupational history as a firefighter and construction worker presented at an urgent care center with signs and symptoms of chronic dry cough, exertional dyspnea, and fatigue. His initial chest X-ray showed interstitial thickening in the middle and lower lobes with pulmonary infiltrates bilaterally. The patient was treated with an outpatient course of antibiotics. A subsequent high-resolution computed tomography (HRCT) scan of the patient's lungs revealed extensive peripheral, bibasilar linear reticulations, interstitial thickening, and subpleural cystic changes, consistent with advanced pulmonary fibrosis. Also noted were diffuse calcifications within the areas of fibrosis. Based on the HRCT findings and negative laboratory tests, the patient was diagnosed with diffuse pulmonary ossification (DPO), the dendriform type. DPO is a rare heterotrophic lung disease characterized by the formation of bone in the lung parenchyma and alveolar spaces. It is categorized as nodular and dendriform; dendriform is associated with chronic respiratory diseases, with characteristics of ramifying spicules of mature bone laid in a serpentine fashion along the alveolar septa, containing bone marrow elements. This case shows a rare form of pulmonary ossification in the setting of chronic fibrotic interstitial lung disease. Interestingly, our patient had a past occupational history as a firefighter with chronic inhalation exposure to particulate matters such as chemicals, smoke, fumes, combustible trash, silica, and alumina, which may all have likely played a role in the pathogenesis of DPO.