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Pulmonary Alveolar Microlithiasis (PAM) is
characterized by deposition of calcium phosphate within the alveolar
airspaces (calcospherites).
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Approximately 300 patients with this disorder have been
reported worldwide.
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The high rate of familial occurrence (>50%)
led to the suggestion of an inborn error of metabolism with autosomal
recessive transmission.
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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.
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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.
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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.
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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.
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There are no special considerations for
patients with a mild form of the disease. However, patients with significant
respiratory impairment ...