Q1: What are the findings on the chest radiograph and computed tomogram of the chest (see 302)?

The chest radiograph reveals diffuse bilateral symmetrical minute nodular shadows involving almost the entire mid and lower zones with sparing of the apices. The heart and mediastinal shadows are totally obscured by these nodules, which are quite dense. The mediastinal window of the computed tomogram shows bilateral diffuse micronodular alveolar calcification.

Q2: What is the likely diagnosis?

The diagnosis is pulmonary alveolar microlithiasis. The chest radiographic picture of “sandstorm” appearance is characteristic and diagnostic of this condition.¹

Q3: What additional investigations should be performed to confirm the diagnosis?

The diagnosis of pulmonary alveolar microlithiasis can most often be made with confidence from the classic chest radiographic pattern and the striking radiological-clinical dissociation. Microliths (round or oval, irregular shaped with concentric laminated appearance) can be identified in sputum, bronchoalveolar lavage fluid, and transbronchial lung biopsy specimens (fig 1). Open lung biopsy is seldom, if ever, indicated.¹ The microliths also bind technetium-99m, which can be a diagnostic adjunct.²

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Figure 3

Microphotograph showing calcific material (calcispherites) within an alveolus and its wall (haematoxylin and eosin stain × 550).

Q4: What is the treatment and prognosis of the condition?

There is no definitive treatment for pulmonary alveolar microlithiasis. Treatment is largely supportive. Bronchopulmonary lavage and corticosteroids have no effect.³ Although usually asymptomatic at presentation, pulmonary alveolar microlithiasis, on rare occasions, can produce functional abnormalities such as progressive breathlessness, pulmonary hypertension, and cor pulmonale. The prognosis is variable. Many patients remain asymptomatic with stable chest radiographs for several years. When disease does progress, it may do so very slowly. Cases have been reported in which respiratory failure and death ensued after a period as long as 40 years.

Discussion

Pulmonary alveolar microlithiasis is a rare disease of unknown aetiology and is one of the few conditions in which gross radiographic changes are present in the face of minor clinical symptoms.⁴ The disease is characterised by the deposition of calcium and phosphorus microliths (calcispherites) within the alveolar space.⁴ Most patients are asymptomatic at presentation and incidentally detected to have an abnormal chest radiograph. About 20%–40% of patients may present with respiratory symptoms such as exertional dyspnoea, dry cough, chest pain, or rarely haemoptysis.¹ The physical examination is usually unrevealing at presentation. As the disease progresses, respiratory insufficiency may develop and be associated with cyanosis, clubbing, and evidence of pulmonary hypertension and cor pulmonale.¹ However, pulmonary function remains normal or slightly impaired for a prolonged period after the diagnosis.

No other pulmonary disease has a radiographic pattern as characteristic and diagnostic as that of pulmonary alveolar microlithiasis.¹ The chest radiograph shows sharply defined nodules, predominantly basal and less than 1 mm in diameter. In gross disease, as in our case, the radiographic opacity is so great that the cardiac borders are completely obscured and the heart shadow may “vanish”. Other radiological findings include presence of bullae at the lung apices, a zone of hyperlucency between lung parenchyma and the ribs (black pleura sign), and pleural calcification.¹

Although the aetiology of this condition is not known, familial occurrence in approximately half of the cases point towards either genetic or environmental factors in the pathogenesis of this condition.⁵ A history of occupational or environmental exposure to inorganic dust is usually lacking in these cases. The microliths typically consist of calcium and phosphorus. However, these patients do not have any systemic disturbances of calcium metabolism.⁶ It is possible that the disease is a manifestation of abnormal calcium metabolism localised only or predominantly to the lungs.

Final diagnosis

Pulmonary alveolar microlithiasis.