Pulmonary lymphangioleiomyomatosis.: Morphological and immunohistochemical findings

Pulmonary lymphangioleiomyomatosis (LAM) is a rare disease affecting only women which is characterised by cystic parenchymal changes and smooth muscle proliferation and has to be considered in the differential diagnosis of interstitial lung disease. The LAM cell is classified as a so-called perivascular epithelioid cell (PEC) showing immunohistochemical co-expression of smooth muscle and melanocytic markers (melanomyopericyte). A total of 18 cases of LAM and 56 cases of various other pulmonary diseases were analysed by immunohistochemistry. For the diagnosis of LAM in transbronchial or open lung biopsies, immunohistochemistry using the antibody HMB 45 is decisive because it shows a highly specific and sensitive, but often only faint reaction for pulmonary LAM. The immunohistochemical detection of nuclear localised microphthalmia transcription factor (MiTF) in LAM as an additional melanocytic marker further emphasises the melanocytic (as well as smooth muscle) line of differentiation within the cells of LAM. Using the concept of a melanomyopericyte, pulmonary LAM could be classified as a hamartomatous interstitial lung disease showing perivascular smooth muscle and partial melanocytic differentiation.