Pulmonary alveolar microlithiasis
Pulmonary alveolar microlithiasis is characterized by the deposition of calcium phosphate in the alveolar air spaces as a result of mutations of the SLC34A2 gene. The diagnosis is often made before symptoms have developed when a chest radiograph is performed for other reasons, and shows a dramatic typical ‘sandstorm’ pattern of diffuse bilateral calcified micronodules. The patient is often symptom-free when the diagnosis is made after a chest radiograph is taken incidentally and reveals calcified micronodules, but typically the disease progresses to respiratory failure over about 10–20 years. Etidronate has led to improvement in some cases that have been detected early. Lung transplantation is the main option in advanced disease. The severity of the disease and prognosis are variable, and this may be influenced by the specific type of gene mutation. Survival of 10–20 years from the onset of symptoms is typical.