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Pulmonary Alveolar Microlithiasis (PAM) is characterized by deposition of calcium phosphate within the alveolar airspaces (calcospherites).

Approximately 300 patients with this disorder have been reported worldwide.

The high rate of familial occurrence (>50%) led to the suggestion of an inborn error of metabolism with autosomal recessive transmission.

Mechanism or cause unknown. Microliths or calcospherites are intraalveolar and interstitial deposits of calcified granules with a diameter of 0.05 to 3.0 mm, consisting of laminated calcium and phosphate complexes in a ratio similar to hydroxyapatite in bone. Groups of multinucleated osteoclast-like macrophages surround the microliths, which are sometimes completely embedded in woven bone or lamellar structured bone containing osteocytes. Apoptotic bodies can be found in the nuclear chromatin and cytoplasm of modified type II alveolar pneumocytes. Microliths seem to act like autologous osteoconductive material when implanted in pulmonary parenchyma and serve as a substrate on which bone can easily be formed. PAM has also been described in association with mitral stenosis; however, the microliths are more uneven and bosselated. Interstitial pulmonary fibrosis is common and pulmonary arterial hypertension may develop.

The radiographic appearance with apical bullae and diffuse micronodular shadows (representing multiple minute calcifications located in the alveoli) is pathognomonic and results in a “sandstorm” or “snowstorm” picture in the chest radiograph. Most of the lesions occur in the posterior part of the lung bases. Heart border and diaphragm often appear obliterated. Bronchoalveolar lavage, transbronchial or open lung biopsy, or sputum analysis are used to confirm the diagnosis. The discrepancy between impressive radiological findings and the lack of clinical symptoms can be striking.

Children with the disease are usually asymptomatic or present either with chronic cough or gradually decreasing exercise tolerance. The physical examination is usually unremarkable. The disease has already been described in premature twins; however, the reduction in pulmonary function usually starts in adulthood and progresses until death results from pulmonary failure in early or mid-adult life. Hitherto, no effective therapy exists to stop the relentless course toward progressive respiratory failure. Lung transplantation may be an option for those with end-stage disease. Until then, inotropic and diuretic drugs, as well as oxygen, are administered for symptomatic relief.

Evaluation of respiratory function should include a chest radiograph and pulmonary function tests. An arterial blood gas analysis is recommended. Appropriate antibiotic therapy and chest physiotherapy may be required for respiratory tract infections. Assess cardiac function including ECG and echocardiography for signs of pulmonary hypertension and right-ventricle stains. Look for evidence of cor pulmonale and optimize cardiac function where possible (diuretics, vasodilators). Laboratory investigations should include a cell blood count, electrolytes, blood urea nitrogen, and creatinine. Sedative premedication should be avoided in the presence of significant respiratory impairment. Postoperative respiratory support may be required and should be arranged preoperatively.

There are no special considerations for patients with a mild form of the disease. However, patients with significant respiratory impairment ...

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