Pulmonary alveolar microlithiasis: two case reports and review of the literature

Abstract

Pulmonary alveolar microlithiasis is a rare diffuse lung disease characterised by deposition of calcium phosphate within the alveolar airspaces. The disease is usually discovered from birth up to 40 yrs of age and is often diagnosed incidentally during radiography of the chest for other reasons. Many patients are asymptomatic and the majority of patients either have normal or restrictive pulmonary function. The clinical course of the disease varies. While it remains static in some patients, it progresses into pulmonary fibrosis, respiratory failure and cor pulmonale in others. With the exception of lung transplantation, there is no known effective treatment for the disease. Although the aetiology remains unclear, mutations of the solute carrier family 34 (sodium phosphate), member 2 gene (the SLC34A2 gene), which encodes a sodium/phosphate co-transporter, are considered to be the cause of the disease. We present two cases of pulmonary alveolar microlithiasis with different mutations in the SLC34A2 gene that have not been previously described, and a review of the literature.

Figure 1.

Case 1. High-resolution computed tomography imaging of the lungs showing intra-alveolar calcifications, mainly subpleural, in posterior and basal parts of the lungs. Paraseptal emphysema is visible. a) Coronal view, b) sagittal view and c and d) axial view of the chest.

Figure 2.

Case 1. Chest radiograph of the lungs showing bilateral sand-like calcific micronodules <1 mm (sandstorm lung), mainly involving the lower zones (as a result of larger volumina rather than selective predilection).

Figure 3.

Case 2. High-resolution computed tomography of the lungs showing bilateral calcifications with increased attenuation involving alveoli, intra- and interlobular septa, fissures and pleura. Signs of fibrosis are visible. Hounsfield unit measurements were very high, representing areas with calcifications.

Figure 4.

Case 1. Lung section from a patient with pulmonary alveolar microlithiasis showing calcified microliths localised in the intra-alveolar spaces. Haematoxylin and eosin staining. Original magnification: a) ×40 and b) ×200.