Background: The aim of this study was to investigate the histological and immunohistochemical features of granuloma annulare (GA) in comparison to deep granuloma annulare (DGA) and granulomatous dermatoses (GDs).
Methods: Our material comprised 13 GA, 8 DGA and 1 atypical granuloma annulare (AGA) in a child with primary immunodeficiency, 10 cases of nonspecific GDs and 1 case of sarcoidosis with cutaneous involvement. The immunohistochemical streptavidin-biotin-Horseradish peroxidase (HRP) analysis was performed on paraffin sections for the detection of CD68/KP-1, CD68/anti-human CD68 clone PGM1 (PGM1), lysozyme, S-100 protein, CD1a, CD3, CD20/L-26, CD4 and CD8.
Results: All 13 GA were characterized by typical palisading and interstitial granulomas. In 6 cases, the lesion extended to the subcutaneous fat, while a considerable perivascular lymphocytic infiltrate without any signs of vasculitis was observed in 10 cases. The DGA were located to the deep dermis and subcutaneous fat, showing palisading granulomas with central necrobiosis. Immunohistochemistry revealed a broad intense expression of CD68/PGM1 in the histiocytic population in all cases, a constant but fainter detection of CD68/KP-1 and a variable one of lysozyme. T-cell markers (CD3, CD4 and CD8) were mainly detected in the perivascular lymphocytic infiltrate of GA and DGA, with CD4+ T lymphocytes predominating over CD8+ in GA and DGA, while CD8+ T lymphocytes was the predominant population in AGA.
Conclusions: CD68/PGM1 is a sensitive and reliable histiocytic marker in confirming the histiocytic nature of equivocal GA and DGA, but the histiocytic immunoprofile is of no particular usefulness in differentiating GA from other GD.