This lorm of colitis is now considered to be one of the commonest causes of chronic diarrhoea in the dog () and appears to be much less common in the cat. However, there is a report of six cases of lymphocytic-plasmacytic colitis in cats (). It may be better described as a syndrome rather than a specific condition as there are many possible aetiological agents which may be responsible for the changes in the colon. Idiopathic colitis appears to affect any breed of dog and cat with no age or sex predisposition. However, cases appear to be more common in German Shepherd dogs. Rough Collies and Labradors.
Unfortunately it is still unusual to determine the cause in the majority of cases of idiopathic colitis, hence the term, but occasionally a specific diagnosis is obtained. In this respect mycotic colitis has been recorded in cats due to Aspergillus spp..
The authors consider that dietary factors may be very important in the aetiology of colitis, because of the response noted to dietary management without drug therapy. Other aetiological agents include Trichuris vulpis infection, Salmonella spp. and Campylobacter spp. Idiopathic colitis may also develop as a sequel to gastroenteritis, secondary to small intestinal disease (especially where bile or fat enters the colon), secondary to systemic toxaemia (e.g. uraemia) or as a component of an immune-mediated disease. Parasitic colitis, histiocytic colitis and granulomatous colitis (which are discussed later in this chapter) may in fact be more specific manifestations or more advanced forms of idiopathic colitis. Further study is required in this area to determine the true aetiology of the majority of idiopathic colitis cases.
Usually patients with idiopathic colitis are bright and show few signs of ill health. Appetite is often good, and there is little evidence of weight-loss in the early stages. Vomiting is observed in 30% of cases; as explained earlier, there is no primary gastric involvement causing the vomiting.
The owner will often report a profuse watery diarrhoea which contains mucus. Blood is seen in less than 20% of cases, as ulceration is not a feature of this condition (). Tenesmus and urgency are variable and dependent on inflammation involving the distal colon and rectum. Usually the faeces are passed in small but frequent amounts. Patients often posture on several occasions but pass only small amounts of faeces. There is rarely evidence of abdominal pain, dyschezia, or dehydration.
Investigation should start by examination of a faecal sample for evidence of infection or endoparasites. Radiographs including barium studies are often unrewarding unless there are gross changes affecting the mucosa. A definitive diagnosis requires endoscopy and biopsy of the colon.
Endoscopy of the colon requires careful preparation or the technique will be unrewarding (). The patient should be starved overnight and receive a warm water enema first thing in the morning. Following successful evacuation of faeces this should be repeated within an hour. The clinician should be aware of the fact that enemas may induce hyperaemia of the colonic mucosa. General anaesthesia is not required for this procedure, and a combination of acepromazine (ACP; C-Vet) at 0.05mg/kg and buprenorphine (Temgesic; Reckitt & Colman) at 0.01 mg/kg, both given intramuscularly, provides adequate sedation and analgesia. The patient should be laid in left lateral recumbency, and the tip of the endoscope lubricated prior to insertion through the anus. Little resentment occurs once this has been achieved and careful examination of the colon can normally proceed without difficulty.
In idiopathic colitis, macroscopic findings on endoscopy may include loss of visualization of submucosal blood vessels and thickening of the mucosa which may assume a granular appearance. It is only rarely that signs of ulceration are observed but it is much more common for the mucosa to be 1’riahlc and bleed easily on passage of the endoscope. The colon may be difficult to dilate and persistent muscle contraction may be observed as the endoscope is passed up the colon.
Multiple biopsy samples should ideally be collected from the rectum, descending, transverse and ascending colon both from apparently normal and obviously diseased sites. Although it is very likely that change in the colon will be diffuse in the majority of cases, focal lesions do occur and would be missed without thorough visual examination and multiple biopsy collection. It is important to emphasize that biopsy samples should be collected even if the mucosa appears normal.
Histopathology will reveal numerous goblet cells, with infiltration of the lamina propria with inflammatory cells such as polymorphonucleocytes, lymphocytes and plasma cells (). Fibrosis will be observed to a variable degree especially where the condition is advanced or has been present for some weeks.
The drug of choice in the treatment of idiopathic colitis is sulphasalazine (Salazopyrin; Pharmacia) at 20 to 40 mg/kg in divided doses. Treatment is often required for at least one month and relapse is relatively common unless the underlying cause is found and removed. The main side effect in dogs is keratoconjunctivitis sicca or dry eye, but this is not common. This condition appears to be due to the sulphapyridine component of sulphasalazine although there is reference to 5-aminosalicylic acid causing dry eye (). A new drug has become available which contains no sulphapyridine, so reducing the risk of side effects. The drug called mesalazine (Asacol; Pharmacia) may be given at 10 to 20 mg/kg. In cats side effects include anorexia and anaemia, and they must be observed for signs of salicylate toxicity. The oral dose of sulphasalazine used in cats should be 25 mg/kg/day ().
In a few cases withdrawal of the drug immediately results in relapse, and in such cases the patient may need to be maintained on a low maintenance dose.
Occasionally dogs will not respond to sulphasalazine alone and prednisolone should therefore be included at 1 mg/kg/day. The authors have observed cases which have not responded to either of these regimes, but have responded to metronidazole (Flagyl; RMB Animal Health) given orally at 30mg/kg/day for dogs and 15mg/kg/day for cats (). In addition to being an antibacterial drug, it also suppresses cell-mediated immunity. It is the latter function which appears to be beneficial in idiopathic colitis.
Dietary management in idiopathic colitis may be of great importance, with various reports suggesting success in treatment of the condition using diet alone. Some 30% of cases appear to respond well to restricted protein diets such as Hills d/d or Waltham selected protein diet. Cats appear to have responded well to lamb, horsemeat and boiled rice or Hills c/d diet (). Dry cereal-based diets should be avoided as they exacerbate the signs of colitis (). However the inclusion of bran to selected protein diets may help to restore normal colonic motility. Until more is known about the importance of diet in idiopathic colitis it is advisable to use one of the above regimes as it may significantly reduce the risk of relapse. In all cases the diet should be fed in at least two meals per day.
Prognosis for this condition should always be guarded as the risk of relapse is quite high, about 30% of cases requiring further treatment. This requirement basically reflects our poor knowledge of the true aetiology in many cases. If dietary factors prove to be important in the aetiology of idiopathic colitis, then the prognosis may be greatly improved in the future, by formulation of exclusion diets.
Selections from the book: “Digestive Disease in the Dog and Cat” (1991)