Quantifying mast cells in bladder pain syndrome by immunohistochemical analysis

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.

The current enzymatic staining method (naphtolesterase) on 10 microm 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 microm sections, staining every third section, or (ii) immunohistochemically with antitryptase on both 10 microm and 3 microm sections, with two and six unstained sections between, respectively. Mast cells were counted according to a well-defined procedure.

The old and the new methods, on 10 and 3 microm sections, showed a good correlation between mast cell counts. When using tryptase staining and 3 microm sections, the mast cell number correlated well with the clinical score (Spearman's rho 0.576; 95% confidence interval 0.155-0.820) and 27 mast cells/mm(2) was the threshold suggesting mastocytosis.

We recommend taking biopsies from the detrusor of patients with suspected BPS and examining them with tryptase-stained 3 microm thick sections, with every seventh section used for quantification; 27 mast cells/mm(2) is considered indicative of mastocytosis.