Pulmonary Alveolar Microlithiasis - Clinico-Radiological dissociation - A case report with Radiological review

Abstract

Pulmonary alveolar microlithiasis (PAM) is a rare chronic lung disease characterized by deposition of intra alveolar calcium and phosphate in bilateral lung parenchyma with predominance in lower and mid zones. Etiology and pathogenesis is not fully understood. However, mutation in SLC34A2 gene that encodes a sodium phosphate co-transporter in alveolar type-II cells resulting in formation and accumulation of microliths rich in calcium phosphate due to impaired clearance is considered the cause of disease. Patients with PAM are asymptomatic till development of hypoxemia and cor pulmonale. It remains static, while in some it progresses to pulmonary fibrosis, respiratory failure and cor pulmonale. We report a case of 44 year old male patient presenting with progressive shortness of breath on exertion for one year in duration with dry cough, more since last six months. Chest radiograph showed dense micronodular opacities giving classical sandstorm appearance. High resolution computed tomography (HRCT) showed microcalcification, subpleural cystic changes and calcified pleura. Lung biopsy showed calcospherites within alveolar spaces.

Keywords: HRCT; Pulmonary Alveolar microlithiasis; Type-II sodium dependent phosphate co-transporter; calcospherites; microliths and micronodular opacities.

Figure 1

A 44 year old male with pulmonary alveolar microlithiasis. Technique: Frontal (posterior to anterior technique) chest radiograph. Findings: (A) Frontal view showing diffuse dense bilateral micronodular opacities (sandstorm appearance) (blue arrow) obscuring the cardiac and diaphragmatic silhouette (red arrow), more in mid and lower zones. There is no pleural effusion. There is no mediastinal or hilar lymphadenopathy. (B) Magnified view of frontal view (A) confirming the presence of micronodular opacities (sandstorm appearance) (blue arrow) obscuring cardiac silhouette.

Figure 2

A 44 year old male presenting with progressive breathlessness and dry cough subsequently diagnosed as pulmonary alveolar microlithiasis. Findings: Axial HRCT thorax at lung window (figures A, B and C) and mediastinal window (Figure D) showing bilateral diffuse intra alveolar (black arrow), as well as interlobular septal calcifications (blue arrow), with calcification of pleura (red arrow). There is no pleural or pericardial effusion, no hilar lymphadenopathy or cardiomegaly. (E) And (F) shows magnified views of axial HRCT thorax at lung window (A) and (B) respectively confirming intra alveolar (black arrow) and interlobular septal calcification (blue arrow) with calcification of pleura (red arrow). Technique: Axial CT images from a 128 slice CT scanner with lung windows figures 2A, B and C (−600 window level and 1600 window width), 120 KVp, exposure time 1279ms, 110 mA, slice thickness 1 mm, non-contrast, 1 mm thickness at 10 mm interval in axial mode. Figure 2D - mediastinal window (60 window level and 400 window width), 120 KVp, exposure time 1279ms, 110 mA, slice thickness 5 mm at 5 mm interval in axial mode, non-contrast.

Figure 3

A 44 year old male presenting with progressive breathlessness and dry cough subsequently diagnosed as pulmonary alveolar microlithiasis. Findings (Hematoxylin-eosin stain sections): shows multiple laminated calcospherites (black arrow) within the alveoli of lung parenchyma suggestive of PAM of lung (100x).