Pulmonary Alveolar Microlithiasis: A Morphologic Study of Six Cases Including TEM and SEM with EDX Analysis and Immunocytochemistry

Pulmonary alveolar microlithiasis (PAM) is a rare lung disease of unknown etiology characterized by calcified spherules which fill alveolar spaces. Although there are approximately 110 cases of PAM previously reported, only 26 have been confirmed by histologic examination. Increased interstitial fibrous tissue is seen in some cases, and some patients develop shortness of breath. However, many patients remain assymptomatic for years following the diagnosis of PAM.Six cases from the files of the Armed Forces Institute of Pathology and Hartford Hospital were studied. Light, scanning and transmission electron microscopic studies were performed as were chemical, immunocytochemical and energy dispersive x-ray analysis. Analyses suggest that they are composed in part of mucopolysaccharides and Ca3(PO4)2. Our findings indicate that microliths form initially around a cellular nidus by the deposition of calcium and phosphate salts from the extracellular matrix vesicles of surrounding cells similar to the method previously demonstrated 1n the formation of bone and psammoma bodies. PAM is not usually associated with Identifiable systemic disturbances in calcium and phosphorus metabolism.