Pulmonary Alveolar Microlithiasis (PAM) is a rare idiopathic autosomal recessive depositional lung condition characterized by widespread intra-alveolar deposition of spherical calcium phosphate microliths or calciferites or calcospherites, despite no recognized issues with calcium metabolism. 1.1 Epidemiology- PAM is present on every continent and does not have a specific racial or regional distribution but it is concentrated mostly in Europe and Asia, and particularly in Turkey, Italy and China. The average age at the time of diagnosis is said to be around 40 years. There is no predilection on the basis of sex. 1.2 Pathogenesis- The disorder is linked to mutations in the type IIb sodium-dependent phosphate cotransporter, which results in alveolar epithelial type 2 cells' incapacity to remove phosphorus ions from the alveolar environment, thus leading to microlith or calcospherite formation in the extracellular fluid (1). Type IIb NaPi is not regulated directly or indirectly by dietary phosphate content via 1,25 dihydroxyvitamin D3. 1.3 Genetic Aspect- The SLC34A2 gene, which encodes a 690-amino acid protein and a 2280-nt mRNA, is found on the short arm of chromosome 4 (4p15) (2). It has 13 exons, the first of which is noncoding. A variety of mechanisms, including frameshifts, chain terminations, and amino acid changes, can result in the homozygous mutations that have been identified (3). The function of the encoding protein can be lost as a result of these mutations, which can also dictate the production of a faulty protein or eliminate gene expression is primarily in the apical portions of alveolar type II cells and is the most common phosphate carrier in the lungs. The reported frequency of familial PAM cases ranges from 36% to 61%, highlighting the significance of genetic factors in the disease's development (4). PAM has been found to occur less frequently between parents and children in a vertical pattern of familial inheritance and more commonly among siblings and cousins in a horizontal arrangement. 1.4 Pathology- Lung biopsy, BAL Fluid and autopsy specimens demonstrate characteristic intra-alveolar lamellar microliths. PAM-related microliths are spherical or ovoid, with sizes ranging from 0.01 to 2.8 mm. The microliths' phosphorus: calcium ratio, as determined by X-ray energy-dispersive spectroscopy, was 1:2, which is compatible with calcium phosphate and calcium hydroxyapatite or carboxyapatite. According to histology, the microliths are periodic acid-Schiff-positive and are made up of calcareous concentric lamellae encircling an amorphous or granular core nucleus (5). 1.5 Clinical Manifestation- The majority of individuals have no symptoms, and PAM is discovered by chance based on radiologic results. Dyspnea, dry cough, chest pain, and occasionally weight loss begins after a slow progression that typically lasts 10 to 20 years. Most patients with severe illness have clubbing, and pneumothorax has been observed as a consequence (6). 1.6 Radiolographic Features- • Chest X-Ray: 1. Sand storm-like calcification distributed throughout the lungs 2. Black pleura sign 3. Apical small bullae • Computed Tomography: HRCT better shows numerous sand-like calcifications throughout the lungs(predominantly in inferior and posterior portions) with subpleural and peri-bronchial distribution (typically ~1 mm) (7). Additional accompanying HRCT features include 1. crazy paving pattern 2. calcified interlobular septa (virtually pathognomonic) 3. small subpleural cysts/emphysema 4. black pleura sign 5. ground glass opacities: tends to be more common in children 6. The vascular tree and borders of the heart and diaphragm are often obscured (“vanishing heart” phenomenon). • Magnetic Resonance Imaging: On T1- and T2-weighted images, the calcific lesions typically exhibit hypointensity or a signal void. In advanced stages of PAM, interstitial fibrosis and thicker alveolar walls are frequently observed; however, the signal strength of these alterations is higher on T2-weighted imaging than on T1-weighted images (8). • PET-CT: On occasion, PET may show high FDG uptake, but primarily in the lung regions that spare calcification. 1.7 Clinical Course- Due to the clinical course's unpredictability and the possibility that diagnostic measures do not accurately reflect the disease's beginning, the long-term survival of PAM patients is yet unknown (9). PAM typically advances in 10–20 years, and the majority of cases have been monitored for up to 10 years following the initial diagnosis; however, a small number of cases have been followed up for more than 40 years. Death usually happens within the fifth decade of life, 10 to 15 years following diagnosis, as a result of cor pulmonale and pulmonary hypertension-induced respiratory failure (10). It has been hypothesized that pulmonary fibrosis and the degeneration of alveolar wall capillaries are caused by microliths irritating alveolar walls over time. Therefore, significant pulmonary hypertension and cor pulmonale are caused by reduced pulmonary capillary beds linked to pulmonary fibrosis. Thus, PAM results in hypoxemia and a restrictive pattern by gradually impairing the architecture of the lungs. Because of these factors, PAM patients, even those initially diagnosed during the asymptomatic stage of childhood, have a dismal long-term prognosis. 1.8 Treatment- Currently, there is no recognized medical or gene therapy. Calcium-chelating agents, diphosphonates, and serial BAL have been ineffective. Lung transplantation should be considered. 1. Case Studies Case 1: A 13-year-old female from Khordha presented with chest pain in bilateral mammary and infra-axillary region for 2years. She had normal antenatal and delivery history. She had history of delayed milestone but ultimately caught up with milestones with normal IQ. Her CNS, CVS, Abdomen and other systemic findings were within normal limit. Investigation:- Chest X-Ray (Figure 1) showed sand like calcification in bilateral lung fields with profusion in mid and lower zone (sand storm appearance). HRCT Thorax (Figure 2) showed crazy paving pattern, calcified interlobular septa, black pleura sign and ground glass opacity Blood routine investigations, Serum Calcium and Phosphate level-which was within normal limit. Exome sequencing–patient could not afford. Bronchoalveolar Lavage fluid-microliths were found to be present when stained the BAL with Von Kossa stain. She was diagnosed as Pulmonary Alveolar Microlithiasis and was started with Injectable Zolendronate, which was given six monthly and Calcium monitoring was done. Case 2: She was sister of the case 1 and is 9 years old. She had no clinical symptoms but, her chest X-Ray showed following findings. Rest other investigations were normal. Chest X-Ray (Figure 3) showed sand like calcification in bilateral lung fields with profusion in mid and lower zone (sand storm appearance). Figure 3 Chest Xray of patient 2 Case 3: 35 years old female presented with chief complain of dry cough only during winters (on and off) for 9 years. She had history of rhinitis. She had come to Respiratory Medicine Department of PGIMER and Capital Hospital for Pulmonary clearance for Hysteroscopy as she had infertility. She had clubbing (Grade 3). Other systemic examination was normal. She had 3 sisters and one brother, all 3 sisters had features of PAM, but the brother had no features of PAM. The elder sister of the patient died due to breast cancer. The patient’s father had succumbed to Brain tumour and he had no features of PAM. The patient had undergone the following tests 8 years back. Investigation: - Chest X-Ray (Figure 5) showed sand like calcification in bilateral lung fields with profusion in mid and lower zone (sand storm appearance). HRCT Thorax (Figure 4) showed crazy paving pattern, calcified interlobular septa, peripheral subpleural cysts black pleura sign and ground glass opacity Blood routine investigations, Serum Calcium and Phosphate level-which was within normal limit. Exome sequencing–patient could not afford. Bronchoalveolar Lavage Fluid-Pale white elevated Granular lesions were seen. Spirometry-showed Restrictive pattern Sputum AFB and CBNAAT was negative for Mycobacterium Tuberculosis. Figure 5 HRCT Thorax- crazy paving pattern, calcified interlobular septa, and ground glass opacit Result: -She was diagnosed as Pulmonary Alveolar Microlithiasis. Case 4: She is the sister of Case 3 and is 30 years old. She had presented to us for dry cough during winter seasons. She had history of infertility. As she had a family history of PAM, we asked her to undergo the following investigation. Investigation: -Chest X-Ray-showed (Figure 6) sand like calcification in bilateral lung fields with profusion in mid and lower zone (sand storm appearance). • HRCT Thorax (Figure 6) -Hyperdense lung parenchyma with calcified thickening of intra and interlobular septa, multiple calcified sand like material in peribronchial and subpleural distribution in both lungs. Crazy paving pattern is seen. Features suggestive of PAM. • Blood routine investigations, Serum Calcium and Phosphate level-which was within normal limit. • Spirometry-showed Restrictive pattern • Sputum AFB and CBNAAT was negative for Mycobacterium Tuberculosis. • Sputum Cytology was normal • Bronchoalveolar Lavage: -Bronchus was normal. • Exome sequencing: -patient could not afford Figure 6 (a)Chest xray and (b)HRCT of patient 4 Result: -She was diagnosed as a case of PAM as her HRCT showed features of PAM and one of her siblings was a diagnosed case of PAM. Case 5: She is elder sister of Case 3. She has passed away due to Breast cancer. She also had similar Chest Xray and HRCT Thorax which were suggestive of PAM.

• Out of my 5 cases only one case had clubbing .2 cases came with cough during the winters, one case had chest pain and other 2 were asymptomatic.2 cases had history of infertility.2 of them had Restrictive pattern in Spirometry. • This disease affects people of all ages and most individuals are asymptomatic in early stages. • Pulmonary Alveolar Microlithiasis is a slowly progressive disease which results in respiratory failure. There is no effective treatment and management is mainly supportive. • Lung transplantation may be needed at advanced stage of disease.

There is currently no effective medical treatment for pulmonary alveolar microlithiasis, an extremely rare condition that has been documented to develop horizontally in siblings and cousins. The usual cause of death is respiratory failure, and the long-term prognosis is not good. At a certain point in the disease's course, a lung transplant is necessary.

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