Pulmonary alveolar microlithiasis (PAM), stone in lungs.

Mis à jour : 3 août 2020

Pulmonary alveolar microlithiasis is a rare autosomal recessive a disease it is slow in development and it is taking several years to develop. The disease is characterized by extensive radiopaque pulmonary alveolar microliths with only mild clinical features (dyspnea, hypoxia. where small stones form and accumulate in the air sacs of the lung. These stones cause inflammation, scarring of lung tissue and reduced respiratory ability resulting in the patient requiring supplemental oxygen.

Stones do not usually form in the lungs. But a rare genetic mutation has been known to cause a deficiency of a sodium-phosphate transporter protein leading to the formation of very tiny stones (sand like) inside the alveoli that progressively gets worse, reducing the air spaces and progressive decline in available oxygen to breathe it is an assumption perhaps no one knows yet the real cause of the PAM.

Some researchers said that PAM can occur due continuous exposure of anyone to dust, smog and polluted environment.

From an epidemiological point of view, Turkey, China, Japan, India, Italy and USA are the nations with the largest case series. A familial occurrence is very frequent among PAM patients and consanguinity of their unaffected parents is common. The clinical course is not uniform and may be rapid or slow; the reasons for this variability are not yet known. Involvement of the male genital apparatus may be more common than is currently known, and a further contribution to the knowledge of PAM may derive from future systematic investigations of the genital tract in males with PAM and, vice versa, from lung investigations in infertile males.

Diagnostic procedures

Diagnostic procedures can be classified into two main groups: imaging and anatomopathological. It include chest radiography, chest computed tomography and high-resolution computed tomography (HRCT); the latter, listed in increasing order of invasiveness, bronchoalveolar lavage (BAL), transbronchial biopsy, open lung biopsy and autopsy.

Currently, there is no medical or gene therapy capable of reducing disease progression. Systemic corticosteroids, the use of diphosphonates has also been proposed to reduce calcium phosphate precipitation in PAM.

Lung transplantation remains the only possible treatment for end-stage disease. Nonetheless, guidelines for the decision as to when transplantation should be undertaken are not available due to the lack of well-defined prognostic indices and the insidious nature of PAM. When either right heart failure or severe respiratory failure requiring oxygen are present, transplantation should be considered. In order to maximize the chances of a successful outcome, patients should be referred before the development of severe right ventricular dysfunction.

PAM is an “orphan” disease and lung transplantation is currently the only effective therapy. However, since the demonstration of the gene responsible for PAM, it is hoped that in the future new therapies may become available, that can reduce the phosphate ions in the alveolar spaces and so arrest or delay the formation of microliths and the progression to interstitial disease

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