Activation of bladder mast cells in interstitial cystitis: a light and electron microscopic study

Interstitial cystitis, a sterile bladder condition, is characterized by urinary frequency, urgency, burning and suprapubic pain. Increasing evidence indicates that interstitial cystitis is a heterogeneous syndrome that reflects an immune response to a variety of triggers. More than 50% of the patients have allergies, 30% have the irritable bowel syndrome and almost 20% suffer from migraine headaches. Increased numbers of mast cells have been reported in interstitial cystitis. Mast cell activation, which is critical if these cells were to be implicated in this syndrome, has been investigated by electron microscopy, which definitively shows mast cell secretion. Recently, methylhistamine, the major metabolite of histamine, and the specific mast cell marker, tryptase, were shown to be significantly elevated in urine of interstitial cystitis patients. Bladder biopsies from 53 patients were analyzed blindly for the number and degree of activation of mast cells using 4 different stains for light microscopy, as well as electron microscopy. Controls included 16 patients with incontinence and chronic bacterial cystitis. Mast cells in controls were less than 10/mm.2 and were all nearly intact. Surprisingly, mast cells from 11 cancer patients averaged 50/mm.2 but almost all were intact. In contrast, mast cells from 26 interstitial cystitis patients averaged 40/mm.2 and more than 90% were activated to various degrees. Therefore, bladder mast cell activation is a characteristic pathological finding in at least a subset of patients with interstitial cystitis.