Histopathology of nonspecific granulomatous prostatitis with special reference to eosinophilic epithelial metaplasia: Pathophysiologic, diagnostic and differential diagnostic correlations.

Recently, we publish two case reports about association of nonspecific granulomatous prostatitis (NSGP) and eosinophilic metaplasia (EM) in benign prostatic epithelium. There is no investigation of large series of this association in medical literature. Aim of the current study is to investigate the frequency of association of NSGP and prostatic EM in a large series of cases and their relationship with the basic prostate pathology: benign prostatic hyperplasia (BPH), National Institutes of Health-category IV prostatitis (so-called histologic prostatitis (HP)), and prostatic adenocarcinoma (PCa).
A retrospective record review for NSGP was performed on a total of 2366 prostatic specimens of all types of material. All cases of NSGP were reviewed for the presence of EM, BPH, and HP. NSGP with EM-cases and control cases with high grade PCa with endocrine differentiation (so-called Paneth cell-like changes) were evaluated immunohistochemically.
NSGP was found in nine cases (0.38%). EM was detected in benign perigranulomatous secretory epithelial cells in 100% of cases with NSGP and were closely associated with BPH and HP. Immunohistochemically, in 55.5% of cases with EM, there was weak focal apical false-positive staining for p504s.
EM is a very common lesion in NSGP and reflects histologically a nonspecific cellular response, connected with repeated inflammation, in close relation with BPH and HP. We speculate that EM might serve as a morphological precursor of the immunologic phase of NSGP. This constant morphological finding could facilitate the histopathological differential diagnosis of NSGP with other types of granulomatous prostatitis and high grade PCa with or without endocrine differentiation.