Pathogenesis, diagnosis, and therapy of feline idiopathic megacolon.

Many cats have one or two episodes of constipation without further recurrence, although others progress to complete colonic failure. Middle-aged male cats are particularly at risk for the clinical continuum of constipation, obstipation, and dilated megacolon. Pelvic canal stenosis and nerve injury are minor causes in the development of this syndrome. In most affected cats, the underlying pathogenesis appears to involve colonic smooth muscle dysfunction. In this group of cats, it is not yet clear whether this disorder represents a primary or secondary (resulting from long-standing constipation and colonic distension) abnormality. Many cats with mild to moderate constipation respond to conservative medical management (e.g., dietary fiber supplementation, emollient or hyperosmotic laxatives, colonic prokinetic agents). Indeed, early use of colonic prokinetic agents is likely to prevent the progression of constipation of obstipation and dilated megacolon in many cats. Some cats may become refractory to these therapies, however, as they progress through moderate or recurrent constipation to obstipation and dilated megacolon. These cats eventually require colectomy. Cats have a generally favorable prognosis for recovery following colectomy, although mild to moderate diarrhea may persist for 4 to 6 weeks postoperatively in some cases.