Localized nodular pulmonary amyloidosis: an uncommon diagnosis with malignancy-like features

An 83-year-old woman presented with a nodule in the upper lobe of her left lung, discovered incidentally on a standard chest X-ray. Chest computed tomography (CT) revealed a peripheral, subpleural nodule with spiculated margins and some calcifications, features highly suggestive of malignancy. A wedge resection of the nodule was performed. Macroscopically, the surgical specimen consisted of a firm, grayish subpleural nodule measuring 6 cm in greatest diameter. Histologically, the lung tissue was replaced by an amorphous eosinophilic acellular deposit that stained brick red with Congo red and exhibited an apple-green birefringence under polarized light. This appearance was consistent with an amyloid deposit. No associated neoplastic lesion was identified. A comprehensive clinical work-up was undertaken to exclude systemic amyloidosis, which yielded negative results. Consequently, a diagnosis of localized nodular pulmonary amyloidosis (NPA) was established. NPA is an exceedingly rare entity, often discovered incidentally, and manifests as a single or multiple subpleural nodules of varying sizes. The radiological appearance is non-specific, leading to misdiagnosis of pulmonary cancer. The definitive diagnosis is made by histopathological examination. Therefore, localized NPA should be considered in the differential diagnosis of a pulmonary nodule. Awareness of this rare condition is crucial to avoid misdiagnosis and unnecessary extensive surgical procedures.