Mast cell and substance P-positive nerve involvement in a patient with both irritable bowel syndrome and interstitial cystitis

Many patients with interstitial cystitis (IC) also have irritable bowel syndrome (IBS), both of which occur overwhelmingly in women, are characterized by pain, and worsen under stress. Bladder and colon biopsies of a female patient with both IC and IBS were evaluated immunohistochemically. There were 40 ± 10 mast cells (MC)/mm² (normal, less than 10) in the bladder, which were degranulated. The colon contained 148 ± 11 MC/mm² (normal, less than 50), mostly close to numerous substance P (SP)-positive nerves. Histamine, methylhistamine, and the unique MC enzyme tryptase were elevated in 24-hour urine during two flare-ups. These results may help explain the concurrent presentation and the painful nature of these syndromes.