Cystic Lung Disease from Protein Deposition: Pathogenesis and Associated Conditions

Purpose of Review

We explicate the development of cystic lung disease from the deposition of protein in the lung. The protein may be in the form of amyloid or non-amyloid (typically immunoglobulin-associated light chains) and is usually seen in the context of three entities: idiopathic light-chain deposition disease, Sjogren's syndrome, and clonal lymphoplasmacytic proliferative disorders. A commonly observed and distinctive feature of the circumscribed cystic spaces is the presence of internal tissue septations.

Recent Findings

The traditional causal association of lung cysts and the pathologic entity of lymphocytic interstitial pneumonitis is untenable. Instead, the development of cysts as a consequence of the degradation of lung extracellular matrix by metalloproteinases, the process initiated with the accumulation of macrophages around deposited protein, is a compelling alternative explanation.

Summary

Lung cysts may be a consequence of parenchymal protein deposition. When internal septations are present, this particular pathogenesis should explicitly be considered, and the presence of associated clinical disorders further pursued.