Quantifying mast cells in bladder pain syndrome by immunohistochemical analysis

OBJECTIVES To evaluate a simple method for counting mast cells, thought to have a role in the pathophysiology of bladder pain syndrome (BPS, formerly interstitial cystitis, a syndrome of pelvic pain perceived to be related to the urinary bladder and accompanied by other urinary symptoms, e. g. frequency and nocturia), as > 28 mast cells/mm(2) is defined as mastocytosis and correlated with clinical outcome. PATIENTS AND METHODS The current enzymatic staining method (naphtolesterase) on 10 mu m sections for quantifying mast cells is complicated. In the present study, 61 patients had detrusor biopsies taken between 2002 and 2005; the patients were given a clinical score, and sections of the biopsy stained with (i) naphtolesterase on 10 mu m sections, staining every third section, or (ii) immunohistochemically with antitryptase on both 10 mu m and 3 mu m sections, with two and six unstained sections between, respectively. Mast cells were counted according to a well-defined procedure. RESULTS The old and the new methods, on 10 and 3 mu m sections, showed a good correlation between mast cell counts. When using tryptase staining and 3 mu m sections, the mast cell number correlated well with the clinical score (Spearman's. 0.576; 95% confidence interval 0.155-0.820) and 27 mast cells/mm(2) was the threshold suggesting mastocytosis. CONCLUSIONS We recommend taking biopsies from the detrusor of patients with suspected BPS and examining them with tryptase-stained 3 mu m thick sections, with every seventh section used for quantification; 27 mast cells/mm(2) is considered indicative of mastocytosis.