Sarcoidosis (II)
Histologically, sarcoidosis is always a diagnosis of exclusion, after infectious agents (mycobacteria or fungi) are ruled out.
The granulomata in sarcoidosis are non-caseating. Early granulomata consist of collections of epitheliod histiocytes which subsequently form giant cells with haphazardly arranged nuclei. In mature granulomata Langhans type giant cells with peripherally arranged nuclei appear. The giant cells may show “asteroid” bodies in their cytoplasm. Intracytoplasmic calcification within the giant cells (Schaumann bodies) can also be seen. Collections of lymphocytes can be present around the non-caseating granulomata. However, palisading is usually not seen.
Later on, the granulomata elicit fibrosis in the myocardium, which over time forms dense large scars , which are larger and more abundant towards the base of the heart.
The image below shows epithelioid multinucleated giant cells surrounded by dense fibrous tissue replacing a vast area of myocardium in an endomyocardial biopsy.
In this image there are multiple granulomata in the"leading edge" of the scarred process. Myocardium is clearly visible pat the granulomatous front. The fibrous nature of the scar is well demonstrated in connective tissue stains such as the Movat stain.
