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Infiltrative Colonic Disease |  |
| Any process that causes a thickening of the wall of the large colon may interfere with absorption of fluid and result in chronic diarrhea, weight loss, and sometimes hypoproteinemia. Thickening may be due to neoplasia, inflammatory cells (such as lymphocytes, plasma cells, macrophages, or eosinophils), or scar formation from previous acute colitis. Rectal palpation may help detect bowel thickening and mesenteric lymphadenopathy. Abdominal fluid cytology may reveal neoplastic cells.
Ultrasonography can be used to determine the degree of thickening of the bowel wall (if the affected area of bowel can be imaged) and may reveal masses in the liver or spleen or on the peritoneal surfaces; a percutaneous biopsy could provide a histopathologic diagnosis of neoplasia or inflammatory cell infiltrate. A biopsy of the rectal mucosa may be beneficial in diagnosis of inflammatory bowel disease but is not without risk to the horse. A surgically obtained colonic biopsy is
more reliable for diagnosis of inflammatory bowel disease (
Inflammatory Bowel Disease) but is more expensive and involves risks of general anesthesia and poor postoperative healing. |
| Treatment of abdominal neoplasia or inflammatory bowel disease is generally unrewarding and seldom undertaken. However, improvement of clinical signs and laboratory parameters with high-dose dexamethasone (0.1 mg/kg, sid) treatment has been reported in 3 horses with clinical signs of alimentary tract lymphoma of T-cell origin. In 2 horses, the high-dose dexamethasone was followed by a lower dosage (0.01-0.95 mg/kg, sid) once clinical improvement
occurred. Favorable responses persisted for >9 mo. The third horse had to be maintained on the higher dose of dexamethasone throughout treatment, as signs recurred whenever the dose was lowered. Clinical signs recurred despite high doses of dexamethasone, and after 2 mo of treatment the horse was euthanized. The mechanism of action of the steroid is speculated to be control of inflammation associated with the condition, as opposed to glucocorticoid-induced apoptosis. |
