A case report of pulmonary amyloidosis recognized by detection of AA amyloid exclusively in alveolar macrophages

Amyloidosis is a rare condition in which tissue deposits of inert fibrillar protein result in organ damage and dysfunction. There are several types of amyloid fibrils. Some of the most common forms are AL (amyloid light chain) protein and AA (amyloid-associated) type of amyloid fibril protein. Pulmonary amyloidosis is relatively common but is usually asymptomatic. Thus, the diagnosis may be easily overlooked. A 78-year-old male with a history of multiple myeloma followed by systemic amyloidosis presented with abnormal chest CT showing diffuse interlobular thickening in the whole lung field with bilateral pleural effusion. Bronchoalveolar lavage and transbronchial biopsy were performed. Due to the patient's poor condition and hemorrhage, only one fragment was available from forceps biopsy. Histologically, there was no amyloid deposition in the lung parenchyma; however, some histiocytes showed eosinophilic granular contents which prompted us to perform additional staining. The cytoplasmic material turned to be positive with direct fast scarlet (DFS) staining and AA amyloid immunostaining. Similar macrophages with AA amyloid were also found in the bronchoalveolar fluid. We experienced a case with AA amyloidosis affecting the lung diagnosed by the presence of intracytoplasmic amyloid in alveolar macrophages. The microscopic changes were so subtle that they may be overlooked. Recognition of amyloid deposition in alveolar macrophages may be an important clue to diagnose pulmonary amyloidosis. Such finding is of particular significance in the small-sized specimens, such as biopsies and cytologic smears.