Immunohistochemical Features of MMP-9 and pSTAT1 in Granuloma Annulare and Sarcoidosis: A Comparative Study of 62 Cases

BACKGROUND: Granuloma annulare (GA) and sarcoidosis are granulomatous inflammatory diseases that share similarities. OBJECTIVE: To identify the histological and immunohistochemical (IHC) features of GA and sarcoidosis. METHODS: A retrospective review of 36 patients with GA and 26 with sarcoidosis was performed. Results from hematoxylin and eosin (H&E) staining and IHC staining of MMP-9 and pSTAT1 within the skin lesions of GA and sarcoidosis were analyzed, and random forest was applied for developing a predictive model. RESULTS: Significantly greater expressions of MMP-9 (especially in elastic fibers, EFs, P < 0.0001) and pSTAT1 (P = 0.0003) were observed in lesion samples of GA versus sarcoidosis patients. In GA patients, MMP-9 was significantly upregulated in the interstitial type (P = 0.0222), while staining of pSTAT1 was positively correlated with the area of mucinous collagen in palisading GA (R = 0.5356, P = 0.0484). In sarcoidosis patients, MMP-9 (R = −0.7127, P = 0.0009) and pSTAT1 (R = −0.5604, P = 0.0067) were found to show stronger expressions in lesions with less lymphocyte infiltration. The predictive model demonstrated an AUC of 0.9675. CONCLUSION: These results indicate that MMP-9 and pSTAT1 might exert roles in granulomatous inflammation in different modes, and the presence of more robust MMP-9 staining in EFs appears to be more suggestive of GA.