Pulmonary alveolar microlithiasis is a rare disorder of unknown etiology recognized by the characteristic radiographic appearance of widespread intraalveolar accumulation of calcific concretions. Despite the striking calcifications, no metabolic abnormalities of calcium or vitamin D have been identified.

No consistent epidemiologic pattern or exposure history to environmental toxins or infectious agents has been established, and autosomal recessive inheritance has been suggested. Onset can occur in childhood, although most cases are reported in adults. Approximately one-half of cases are familial, identified among asymptomatic siblings after diagnosis of the incident case. Excluding the secondary cases, more than 400 cases have been reported worldwide.

Frequently, the illness is discovered in asymptomatic patients when a chest roentgenogram is taken for an unrelated illness. When symptoms develop, cough often is the chief complaint.

The characteristic chest roentgenogram shows fine bilateral diffuse, “sandlike” micronodulation, most prominent in the bases, often obliterating the diaphagmatic, mediastinal, and cardiac borders (Fig. 241.1). An unusual feature of this disease is the striking radiographic changes in contrast to the relative paucity of physical findings. High-resolution computed tomography more precisely defines the extent and severity of the disease. Bronchoalveolar lavage and open lung biopsy show calcispherites in recovered fluid and in the alveolar spaces, respectively. In children, the differential diagnosis of this miliary pattern includes disseminated tuberculosis, healed disseminated histoplasmosis, and other conditions associated with diffuse calcification such as chronic renal failure, hyperparathyroidism, or vitamin D intoxication. Pulmonary function tests show restrictive lung disease, the severity of which correlates with the degree of interstitial lung disease. Histologically, numerous laminated calcispherites (average diameter 1 mm) are found within the alveolar spaces with either normal or thickened fibrotic interstitium. This appearance is distinct from other disorders associated with metastatic and dystrophic calcification in which calcification occurs in the interstitial or vascular components. Although additional evaluations (bronchoalveolar lavage, 99m-technetium bone scintigraphy, computed tomography, and transbronchial or open lung biopsy)
have been performed, none usually provides more diagnostic information than do the clinical history and plain-film roentgenogram of the chest.