Granulomatous prostatitis on needle biopsy.

OBJECTIVE: To assess pathologic findings of granulomatous prostatitis (GP) on needle biopsy.

DESIGN: Ninety-four cases of granulomatous prostatitis were culled from 25,852 (incidence 0.36%) consecutive men who underwent needle biopsy; clinical correlations were obtained for 75. Cases were categorized as nonspecific (NSGP, 77.7%), infectious (IGP, 18.1%), or indeterminate (4.3%) granulomatous prostatitis based on histologic and clinical criteria.

SETTING: Consecutive cases from a large commercial laboratory and consultation cases.

RESULTS: All cases of IGP had a history of prior bacillus Calmette-Guerin therapy for transitional cell carcinoma. Histologically, 57% of NSGP cases mimicked infection and 4% mimicked cancer. Caseating necrosis was identified in 76% of cases of IGP. Significant numbers of eosinophils were found in 68% of NSGP cases, but in only 12% of IGP cases. In no case was eosinophilia documented in peripheral blood. Multinucleated giant cells were absent or rare in 69% of NSGP cases. Significant numbers of neutrophils were found in 53% of NSGP cases, but in only 29% of IGP cases. At the time of biopsy, cancer was clinically suspected in 55% of cases categorized as NSGP and 73% categorized as IGP. Serum prostate-specific antigen ranged from less than 0.5 ng/mL to 114 ng/mL (mean 12.7 ng/mL) in NSGP and from 0.9 ng/mL to 9.7 ng/mL (mean 4.2 ng/mL) in IGP. Digital rectal exam was abnormal in 69% and 91% of NSGP and IGP cases, respectively. Transrectal ultrasound was abnormal in 77% and 100% of NSGP and IGP cases, respectively. There was no correlation between the extent of core involvement with either clinical impression, prostate-specific antigen levels, transrectal ultrasound, or digital rectal exam. Thirty additional granulomatous prostatitis cases on needle biopsy were obtained from the consultation files of one of the authors. The major difference in this group was a higher percentage of cases histologically mimicking cancer (20%); two cases were misdiagnosed by the referring pathologist as high-grade cancer.

CONCLUSIONS: While NSGP is the most common granulomatous prostatitis seen on needle biopsy, bacillus Calmette-Guerin granulomas are not seen infrequently. Lesser known histologic features of NSGP were the frequent finding of neutrophils and eosinophils and infrequent multinucleated giant cells. Granulomatous prostatitis may be clinically indistinguishable from cancer, and NSGP may also histologically mimic carcinoma.