Microcrystalline Cellulose Aspiration Presenting as Interstitial Lung Disease Diagnosed via Transbronchial Lung Cryobiopsy.

Chronic occult aspiration is an underrecognized cause of airway-centered and interstitial lung disease and can mimic inflammatory or fibrotic pulmonary disorders. Microcrystalline cellulose, a widely used pharmaceutical excipient, can provoke a foreign body giant cell reaction when aspirated into the lower respiratory tract. Because aspirated material may be focal, it can be missed on small biopsy specimens, delaying diagnosis and leading to inappropriate treatment. We report a case of a 54-year-old woman with progressive exertional hypoxemia and diffuse ground-glass opacities initially concerning for interstitial lung disease. Transbronchial lung cryobiopsy demonstrated polarizable foreign material consistent with microcrystalline cellulose, accompanied by a foreign body giant cell reaction, establishing aspiration-related lung disease. This case emphasizes the importance of considering pill excipient aspiration in patients with recurrent aspiration risk and highlights the diagnostic value of transbronchial lung cryobiopsy in unexplained interstitial lung disease.