Pulmonary alveolar microlithiasis (PAM) is characterized by the formation of calcium microlith in the alveoli due to defective clearance of phosphates. The clinical traits of PAM are heterogeneous and lung deterioration progresses at different speeds even when microliths appear early. The hallmark of PAM is clinico-radiological dissociation with typical imaging findings that correlate with specific pathological findings [1]. This report highlights the clinico-radiological dissociation and the tests available for the diagnosis of PAM.

Three children were diagnosed as PAM between 2015 and 2019. The first case was a 5-year-old girl (14.6 kg) who presented with complaints of fever, cough and poor appetite for seven months. Physical examination was normal. Imaging showed lung infiltrates suggestive of interstitial lung disease (Fig. 1 and 2) but the open lung wedge biopsy showed calcific nature of the lesions confirming the diagnosis (Web Fig. 1). The second one was a 4½-year-old girl (16.3 kg) who presented with recurrent fever, poor appetite and cough. The radiological imaging showed micronodular mottling on both lung fields. Broncho-alveolar lavage (BAL) demonstrated pus cells with moderate Streptococci. Video assisted thoracoscopic lung biopsy demonstrated air-spaces with innumerable tiny calcified bodies that are concentrically laminated with radial striations in the intra alveolar lumen consistent with pulmonary alveolar microlithiasis. The third case was a 12-year-old girl (17.3 kg) who presented with fever, weight loss and poor appetite for one year. She was treated for tuberculosis. Imaging showed calcified micronodule lesions on the midzones of both the lungs and ground glass opacities. Pulmonary function testing showed a mild restrictive pattern. BAL demonstrated Moraxella spp.

Fig. 1 Chest radiograph showing diffuse reticulonodular opacities in both lung fields.	Fig. 2 Computed tomography lung window showing calcified micronodule lesions on the midzones with ground glass opacities.

PAM is reported worldwide with more than half of the cases from five countries (Turkey, China, Japan, India, and Italy) [2]. It is often diagnosed incidentally during radiography of the chest [3]. All the three children in the present study were girls, contrary to a study from Turkey which reported six boys with PAM and a familial inheritance [4]. Studies have identified mutations causing decreased cellular uptake of phosphate leading to formation of intra-alveolar microliths [5].

The clinico-radiological dissociation with significant radiological findings in the absence of lower respiratory features like dyspnea and retractions have been reported earlier [6]. As the evolution of PAM is insidious, diffuse micronodular opacities may appear as miliary shadows in the chest radiograph leading to misdiagnosis of tuberculosis. CT chest demonstrated multiple calcified micronodules in both lungs, subpleural regions, and in the cardiac margins in all three affected children. PAM is usually diagnosed on the basis of a typical radiological pattern like a sand-like micronodulation of calcific density diffusely involving both lungs with basal predominance. Presence of this pattern may preclude the need for a lung biopsy. SLC34A2 is implicated as the defective gene [5]. Paucity of symptoms and clinico-radiological dissociation may invite unnecessary investigations in the initial stages of the disease when PAM should be kept as a close differential.

1. Ferreira Francisco FA, Pereira e Silva JL, Hochhegger B, Zanetti G, Marchiori E, et al. Pulmonary alveolar micro-lithiasis. Respir Med. 2013;107:1-9.

2. Castellana G, Gentile M, Castellana R, Resta O. Pulmonary alveolar microlithiasis: Review of the 1022 cases reported worldwide. Eur Respi Rev. 2015;24:607-20.

3. Jönsson ÅLM, SimonsenU, Hilberg O, Bendstrup E. Pulmonary alveolar microlithiasis: Two case reports and review of the literature. Eur Resp Rev. 2012;21: 249-56.

4. Senyigit A, Yaramis A, Gürkan F, Kirbas G, Büyükbayram H, Nazaroglu H, et al. Pulmonary alveolar microlithiasis: A rare familial inheritance with a report of six cases in a family. Respiration. 2001;68:204-9.

5. Huqun, Izumi S, Miyazawa H, Ishii K, Uchiyama B, Ishida, et al. Mutations in the SLC34A2 gene are associated with pulmonary alveolar microlithiasis. Am J Respir Crit Care Med. 2007;175:263-8.