Pulmonary Alveolar Microlithiasis: A Unique Case of Familial PAM Complicated by Transplant Rejection

Abstract

Background: Pulmonary alveolar microlithiasis (PAM) is a rare lung disease characterized by the deposition of calcium phosphate microliths or calcospherites, within the alveolar airspace. Typical imaging findings demonstrate a "sandstorm" appearance due to bilateral, interstitial sand-like micronodularities with basal predominance.

Methods and results: We describe an unusual case of a 48-year-old male with severe, familial PAM ultimately treated with a bilateral lung transplant.

Conclusions: PAM is a rare lung disease caused by a mutation in the SLC34A2 gene, which encodes for a sodium-phosphate cotransporter in type II alveolar cells, leading to accumulation of intra-alveolar phosphate causing microlith formation. PAM has an indolent course but can progress to chronic hypoxic respiratory failure, ultimately requiring lung transplant, the only known effective treatment.

Figure 1

Radiologic findings consistent with PAM. (a) Chest X-ray demonstrating diffuse bilateral interstitial hyperdensities with bibasilar predominance consistent with severe interstitial lung disease. (b) Transverse view of chest CT showing diffuse ground-glass opacities, peripheral cystic change, and diffuse areas of fine calcification.

Figure 2

Histologic examination of explanted lung tissue. (a) 4x H&E sections of bilateral lung parenchyma demonstrated similar findings consisting of numerous microliths filling alveolar spaces, diffuse interstitial fibrosis, and focal osseous metaplasia. (b) 10x higher magnification showing the characteristic concentric calcification of the microliths and focal osseous metaplasia.