Overview.
Pulmonary alveolar microlithiasis (PAM) is a rare disease of numerous microliths present in the alveoli. The etiology of this disease is unknown. It can occur at all ages, with no significant gender differences. The main clinical manifestations are dyspnea, cyanosis, hemoptysis, and mortar and pestle formation. Patients may also be asymptomatic or have characteristic clinical manifestations and radiographic inconsistencies. There is no specific treatment for this disease, and prevention should be the mainstay of daily life by reducing the amount of exercise or reducing the intensity of labor.
Etiology
The etiology of this disease is unknown.
1. It may be a pulmonary manifestation of systemic metabolic disease, in which calcium and phosphorus indicators are normal in blood tests. No associated virus has been isolated from lung tissue.
2. It may be autosomal recessive inheritance. According to the theory of molecular genetics, the traits of organisms are closely related to the metabolism of organisms, any metabolic process is a biochemical process, and the hereditary characteristics of organisms depend on the order of nucleotides on the DNA chain of chromosomes. The extensive deposition of calcium and phosphorus vesicles in the alveoli of the lungs in this disease may be due to a “loss of control” of biochemical regulatory genes. The mutant gene can be transmitted from parent to offspring in consanguineous gametes if there is a small error in the gene or code.
3. The disease may also be due to inborn abnormalities of calcium and phosphorus metabolism in the lungs.
Symptoms
Most patients are asymptomatic before the onset of the disease and are often detected on physical examination. Characteristic clinical manifestations and radiographic inconsistencies may develop, with severe dyspnea, cyanosis, hemoptysis, and pestle-like digit formation. Rarely, cough and sputum are seen, and some patients may cough up microscopic stones. Decreased breath sounds at the base of the lungs and even respiratory failure, right ventricular hypertrophy and cardiac insufficiency.
Examination
1. Laboratory examination
Sputum or bronchoalveolar lavage fluid (BALF) may detect microstones.
2. Other auxiliary examinations
(1) Imaging examination The main method of diagnosing this disease is imaging examination. x-ray mainly shows diffuse distribution of fine sand-like microcrystalline shadows in both lungs, which may be accompanied by pleural thickening and may be associated with cardiac insufficiency. It may be accompanied by pleural thickening, which may be due to the visual effect of the deposition of microstones in the subpleural lung parenchyma, producing a dense white line in the neighboring pleura, rather than true pleural thickening. Follow-up chest radiographs show an increase in the size of the microstones. Rupture of the subpleural pulmonary bullae may produce spontaneous pneumothorax, and rupture of the intrapulmonary bullae may produce interstitial emphysema. Examination with 99m TC phosphorus flash scanning reveals the presence of active metabolic exchange through the alveolar capillary membranes if microcrystalline uptake tracers are found.
(2) Lung function tests Progressive changes in lung function occur. Lung function is not abnormal in the early stages and may progressively show ventilatory dysfunction, reduced diffusion function, and hypoxemia. Restrictive ventilatory dysfunction may appear when the disease is aggravated. Respiratory failure may occur in advanced stages.
Diagnosis
The diagnosis of the disease is generally not difficult based on the history, typical X-ray findings (inconsistency between clinical manifestations and X-rays). Few patients require confirmation by sputum, bronchoalveolar lavage to obtain stones, or by fiberoptic bronchoscopic lung biopsy.
Differential diagnosis
Some diseases present with similar diffuse pulmonary nodules or cornified shadows on X-ray and require differential diagnosis:
1. Tuberculosis of the granular type
With symptoms of tuberculosis poisoning, chest X-ray shows that in the acute stage, it presents diffuse distribution of size, density, distribution of three uniform, clear edge corn-like shadows, but the density is lower than that of alveolar micronodules; in subacute and chronic hematogenous disseminated tuberculosis, there are foci of varying sizes and densities in the two upper and middle lung fields that are different in their distribution from that of alveolar micronodules.
2. Silicosis
There is a history of silica dust inhalation. Lung X-ray shows nodules of unequal size, interspersed with fibrous reticular shadows. Stage I silicosis has enlarged hilar lymph nodes; Stage III silicosis can be seen in the upper part of the two lungs, often with fused silica nodule shadows.
3. Idiopathic pulmonary hemosiderosis
Mostly seen in children, with repeated hemoptysis, shortness of breath, fever, cyanosis and other symptoms. The X-ray of both lungs shows nodular shadows or flaky infiltration with light density of varying sizes, and the shadows can be absorbed after stopping hemoptysis, or a small amount of reticulated or fibrous shadows can be left behind.
Treatment
There is no specific treatment, and the efficacy of bronchoalveolar lavage is not obvious. In order to avoid shortness of breath, the amount of exercise should be reduced or the intensity of labor should be lowered in daily life, and respiratory and pulmonary infections should be prevented.
Prognosis
Some patients develop pulmonary heart disease and respiratory failure after several years.
Prevention
Avoid or reduce the inhalation of dust and smoke, and avoid active and passive smoking to avoid aggravation of lung damage. Prevent and promptly treat upper and lower respiratory tract infections. Give home oxygen therapy when cyanosis occurs to delay the onset of pulmonary hypertension and chronic pulmonary heart disease.