A 68-year-old man with elevated serum PSA underwent protate needle biopsies. Representative cross-sections were submitted.
Sections revealed fibrous stroma with reactive and atypical stromal cells and foci of eosinophic deposits (Fig.1). No prostatic epithelium was present to evaluate. Immunostain for CD34 was negative (Fig.2) and Congo red stain was positive (Fig.3).
The differential diagnosis considerations included:
Eosinophilic deposits in the prostate of an adult man
Key Features:
Amyloid can be found in the prostate as an incidental finding in corpora amylacea, stroma, and blood vessels. Most corpora amylacea in the prostate stain for amyloid because they are Congo red positive, with apple-green birefringence obtained by crossed polarizing filters. The amyloid protein in protatic corpora amylacea is β2 microglobulin, as shown by immunohistochemical staining. In primary prostatic amyloidosis both stromal and blood vessel wall involvement have been documented. The incidence in consecutive unselected cases has vaied from 0.6% to 10% of patients. The average age of patients with prostatic amyloidosis ranges from 66 to 86. Incidental prostatic amyloidosis has been reported in 38% of multiple myeloma patients. No patient with secondary amyloidosis has been initially diagnosed with amyloidosis based on finding amyloid in the prostate. No gross abnormalities referable to prostatic amyloidosis have been communicated. Microscopically, prostatic stromal amyloid has been portrayed as stromal areas of irregular nodules of amorphous, highly eosinophilic material. The amount of amyloid deposit is variable. The location within the stroma is also variable and can be periglandular or distant from glandular epithelium. Congo red is the most commonly used stain in the characterization of prostatic amyloid. Little is known of the type of amyloid deposited in prostatic stromal and vascular amyloidosis because immunohistochemical study has not been preformed. In contrast, seminal vesicle amyloidosis, which is present in about 10% to 15% of patients has been much better studied. It is not known whether prostatic amyloidosis is related to seminal vesicle amyloidosis. The pathogenic basis for the primary accumulation of amyloid in the prostate is also unknown.
Prostatic amyloidosis should not been confused with prostatic stromal collagen, including collagenous micronodules in prostatic carcinoma. When injected periurethrally to treat incontinence, collagen could also be sampled by prostate or prostatic fossa needle biopsy and is also in the differential of urethral and prostatic amyloidosis. Blood vessel hyalinization should not be mistaken for prostatic vascular amyloidosis. A congo red stain will resolve any question about the nature of amorphous deposits in prostatic stroma or vessels. It has not been established whether identification of amyloid in prostatictissue should prompt a search for systemic amyloidosis.
