Spontaneous remission of the micronodular pattern in cryptogenic organizing pneumonia.

Organizing pneumonia (OP) is a common interstitial lung disease, pathologically characterized by polypoid granulation tissue in the alveolar ducts and alveoli. In clinical practice, OP occasionally presents as non-resolving pneumonia. The typical radiographic pattern of OP is characterized by dense consolidation with ground-glass opacities. Diffuse micronodular pattern of OP (MNOP) is a rare radiographic manifestation that mimics non-resolving bronchiolar diseases such as pulmonary tuberculosis or hypersensitivity pneumonitis. Steroid therapy is usually effective for MNOP; however, spontaneous remission in MNOP has never been reported. Herein, we report a case of a diffuse micronodular form of cryptogenic OP (COP) that was diagnosed via transbronchial biopsy (TBB) and resolved spontaneously within a few months. Our case highlights that MNOP may resolve spontaneously similar to other forms of OP, and mild cases may be under-recognized. Furthermore, careful observation could be an option for managing MNOP with mild and non-progressive symptoms.