PULMONARY ALVEOLAR MICROLITHIASIS

Pulmonary alveolar microlithiasis (PAM) is a rare chronic disease of unknown etiology and pathogenesis, characterized by the widespread presence in the alveoli of minute calcific deposits known as microliths. The deposits are probably due to an inherited defect with autosomal recessive transmission. The disease is present worldwide and a recent review of the literature counted 576 cases. It has been most frequently reported in Europe, followed by Asia. The nation with the highest number of reported cases is Turkey, followed by Italy in second place. Cases of PAM are defined as (1) ‘familial’ when two or three, or in exceptional cases even four or five siblings are affected, and (2) ‘sporadic’ when screening of the rest of the family yields negative results. In most cases patients have mild clinical symptoms, contrasting with the severe radiographic appearance: these are characteristic features that should raise the suspicion of PAM. High-resolution computed tomography (HRCT) has made it possible to define the extent and severity of the disease more precisely. Bronchoalveolar lavage (BAL) and transbronchial biopsy (TBB) confirm the presence of microliths in the alveoli. Symptomatic cases generally feature the presence of effort dyspnea, a cough, chest pain, asthenia, finger clubbing, crepitations, and a restrictive defect revealed by lung function assessment. Macroscopic findings include markedly increased lung weight. The disease is initially endoalveolar, then involvement of the interalveolar tissue begins to appear and subsequently progression is observed, with the development of pleural calcifications, emphysema bubbles, and ossification nodules. Treatment is at present only palliative. Steroids have proved to be inefficacious while the results of administration of sodium etidronate and the BAL technique are controversial. Affected individuals may undergo progression to end-stage disease requiring lung transplantation.