An Extremely Rare Case of Pulmonary Alveolar Microlithiasis
Year: 2025
Type: article
Study design: Case Report
Abstract: QUESTION A 27-year-old female presented with shortness of breath for 2 years duration with a dry cough and chest pain. The patient developed dyspnea, which is initially MMRC (Modified Medical Research Council) grade 1, progressing to MMRC grade 2. She is a housewife. There was no history of similar complaints in the past. There was no clubbing, cyanosis, or peripheral edema on clinical examination. On chest auscultation, it revealed pan-inspiratory fine crepitations present in the bilateral infrascapular and infra-axillary regions. Cardiac auscultation and electrocardiography were normal. Blood counts and serum biochemistry were normal. The pulmonary function test showed a restrictive pattern. Induced sputum for cartridge-based nucleic acid amplification test done. Mycobacterium tuberculosis was not detected. The human immunodeficiency virus test was negative. A chest skiagram [Figure 1] and computed tomography of the thorax [Figures 2 and 3] were done as a part of the workup and revealed the following pictures. Please identify the condition.Figure 1: Chest skiagram PA view shows diffuse dense bilateral micronodular opacities (sandstorm appearance)Figure 2: Axial High resolution computed tomography (HRCT thorax) at the lung window shows bilateral diffuse intra-alveolar as well as interlobular septal calcifications with calcification of pleuraFigure 3: Axial High resolution computed tomography (HRCT thorax) at the mediastinal window shows bilateral diffuse intra-alveolar as well as interlobular septal calcifications with calcification of pleura, shows Black pleura sign (a vertical linear radiolucency between ribs and lung parenchyma) ANSWER Pulmonary Alveolar Microlithiasis (PAM). DISCUSSION Chest skiagram [Figure 1] shows diffuse dense bilateral micronodular opacities (sandstorm appearance). Axial high-resolution computed tomography (HRCT) thorax at the lung window [Figure 2] and mediastinal window [Figure 3] show bilateral diffuse intra-alveolar as well as interlobular septal calcifications with calcification of pleura. PAM is a rare disease with poorly defined etiology and pathogenesis, characterized by numerous microcalculi within air spaces.[1] More than 1000 cases have been reported worldwide. It appears to be due to autosomal recessive inheritance due to mutations of the SLC34A2 gene, which encodes a type-IIb sodium-dependent phosphate cotransporter. SLC34A2 is primarily expressed in the lung in alveolar type II cells. These cells are responsible for the production of surfactant. Loss of function of a gene due to mutation leads to decreased cell uptake of phosphate, which leads to the formation of intra-alveolar microliths as a result of phosphate chelating calcium in extracellular fluid.[2] Lung biopsy shows characteristic intra-alveolar lamellar microliths. In advanced cases, microliths are seen in interlobular septa, bronchovascular bundles, and subpleural space, where fibrosis and ossification are often observed.[3] Many patients are asymptomatic and either has a normal pulmonary function or a mild restrictive pattern. Symptomatic patients have dyspnea and a nonproductive cough. In some other cases, it worsens at different rates, leading to pulmonary fibrosis, respiratory failure, and cor pulmonale.[4] Characteristic chest radiographs show fine, sand-like micronodulation of calcific densities bilaterally involving mainly middle and lower zones with a sandstorm appearance. High concentration of microliths within the periphery of the secondary pulmonary lobule is responsible for the thickening of interlobular septa and micronodulation on HRCT. Black pleura sign–a vertical linear radiolucency between ribs and lung parenchyma can also be seen, which is secondary to subpleural cystic changes often seen on HRCT and pathological evaluation. Differential diagnosis of PAM includes pulmonary alveolar proteinosis, sarcoidosis, silicosis, pulmonary hemosiderosis, amyloidosis, and metastatic calcification in chronic renal failure. No effective treatment for PAM is known except for lung transplantation. Therapeutic bronchoalveolar lavage and corticosteroids are ineffective. The recurrence of disease after lung transplantation was not reported yet. Disodium acetedronate, known to inhibit microcrystal growth of hydroxyl appetite, used in the dose of 10 mg/kg/day orally for 1 year, can cause considerable regression of calcific densities in PAM.[3] Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
Source: Journal of Advanced Lung Health
Institution: Government of Haryana
Language: English
Subfield: Pulmonary and Respiratory Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: diamond
OpenAlex ID: W4412523646