Diseases of the Colon

By | April 7, 2015

Acute colitis

Acute large bowel diarrhoea is common and generally self-limiting. Potential causes include diet, bacteria and/ or their toxins, viral agents and parasites. Rarely is the underlying cause identified, necessitating non-specific symptomatic treatment. Reduced oral intake of a low fat, highly digestible diet, fed at frequent intervals is recommended. Either nutritionally balanced home-made rations or ready-made commercial Gl diets can be used. Hypoallergenic diets may be used successfully in some patients. Fibre supplementation is often prescribed for large bowel diarrhoea, since it affects large bowel function by normalizing motility, by binding colonic irritants, and by nourishing and protecting the colonic mucosa (e.g. via fermentation of soluble fibre into SCFAs).

Acute colitis which is non-responsive to dietary management may require anti-diarrhoeal drugs (). These drugs (e.g. motility modifiers such as diphenoxylate or loperamide) are generally reserved for short-term use of 3-5 days duration. Antibiotics should not be routinely administered in cases of acute colitis of undetermined cause because of their adverse effects on normal intestinal flora and their tendency to promote resistant strains of bacteria.

Parasitic colitis

Parasitic colitis is a common cause for colitis affecting dogs in parts of Europe and the United States. Trichuris vulpis (whipworms) may infest the proximal colon causing intermittent diarrhoea with blood and mucus at the end of the stool. Eosinophilia, anaem ia and hypoalbuminaemia are possible, although uncommon. Diagnosis is made by finding eggs in faeces or parasites during colonoscopy. The treatment of choice is fenbendazole. Due to the prepatent period of Trichuris, therapy should be repeated at 3 months. Trichomoniasis caused by Pentatrichomonas hominis infection may occur in both dogs and cats. However, diarrhoeic animals with large numbers of organisms may have other causes for diarrhoea. Motile trophozoites identified on direct faecal smears should be treated. Metronidazole typically eliminates the organism, although re-infection may occur. Worming is indicated in cases with mild signs of large bowel diarrhoea and when faecal parasite examinations are negative.

Infectious disorders

Bacterial colitis

Enteropathogenic bacteria produce colonic disease by invading the epithelium (i.e. enteroinvasive bacteria) or by attaching to the mucosal surface without invading it and producing enterotoxins (i.e. enferotoxigenic bacteria) that are cytotoxic or that promote fluid and electrolyte secretion. Enteropathogenic bacteria of most clinical importance include Salmonella species, Campyiobacterjejuni and Clostridium spp.

Salmonellosis: Salmonella spp. are Gram-negative bacilli which are occasionally isolated from the faeces of normal and diarrhoeic dogs and cats. Clinical salmonellosis is quite uncommon indicating a prevalent carrier state. Infection is transmitted by the faecal-oral route or through ingestion of contaminated food or water. Rates of infection are greatest in young animals and in kennelling facilities with overcrowding and poor sanitation. Salmonella enterotoxicosis is characterized by acute, watery or mucoid diarrhoea, vomiting, fever, dehydration, anorexia and tenesmus. Most animals recover in 3-4 weeks, although the shedding of organisms may persist for up to 6 weeks. Rarely, salmonellosis progresses to a fatal bacteraemia or endotoxaemia.

Diagnosis of salmonellosis requires an appropriate history and clinical picture, microbiai growth of the organism and elimination of other causes for enterocolitis. Therapy with antibiotics is controversial. Antibacterial therapy may alter the local microbial ecosystem, which prolongs shedding of Salmonella organisms and encourages the development of a carrier state. Antibiotics are indicated when Salmonella invasion results in clinical (fever, malaise, bloody diarrhoea)’or laboratory (neutropenia, hypoglycaemia) evidence of bacteraemia and endotoxaemia.

Campylobacteriosis: Campylobacter jejuni is a Gram-negative, microaerophilic bacteria that is an important pathogen in both humans and animals. It is probably transmitted via the faecal-oral route including contaminated food and water. Clinical signs are attributed to mild enterocolitis or enterotoxin-mediated secretory diarrhoea, which causes watery, mucoid diarrhoea that occasionally contains blood. In some animals, diarrhoea may be chronic or intermittent.

A presumptive diagnosis of campylobacteriosis may be based on signs, housing environment, and the observation of ‘seagull shaped’ organisms and increased faecal leucocytes on rectal cytology. Definitive diagnosis requires culture of Campylobacter from fresh faeces using selective media and growth conditions. Antibiotic therapy is usually curative. First choice antibiotics are erythromycin (10-15 mg/kg p.o. q8h for 7 days) or enrofloxacin (5 mg/kg p.o. q24h). Faecal cultures should be repeated one month following antibiotic therapy to ensure that infection has been eliminated. Antibiotic therapy may not eradicate the bacterium and re-infection is likely in kennel situations.

Clostridial colitis: Clostridium perfringens is a Gram-positive, obligate anaerobe that is part of the normal microflora in dogs and cats. Under ideal conditions, C. perfringens produces enterotoxins that cause large bowel diarrhoea. Colitis caused by C. perfringens is a major cause of acute, nosocomial and chronic large bowel diarrhoea, which occurs frequently in dogs. The diarrhoea is typically soft and may or may not contain blood and mucus. Another clostridium, C. difficile, has been isolated from both diarrhoeic dogs and cats, possibly subsequent to antimicrobial suppression of the resident flora, but is a considerably less common cause for bacterial colitis.

A presumptive diagnosis of C. perfringens infection is based on identification of increased faecal leucocytes and populations of large spores on faecal cytology and an assay for faecal enterotoxins using a reversed passive latex agglutination test. Routine dosages ofamoxicillin, metronidazole or tylosin orally administered for 5-7 days are usually curative. Some patients also respond to high fibre diets, which alter the colonic microenvironment making conditions unfavourable for the spores to germinate. Prognosis for control is excellent.

Yersiniosis: Yersinia enterocoiitica is a motile, Gram-negative facultative anaerobic bacteria that is uncommonly found in dogs. The organism is transmitted to dogs via the faecal-oral route or ingestion of contaminated food and water. Yersinia organisms may then invade the mucosa and/or produce enterotoxins, causing acute or chronic diarrhoea. Diagnosis requires growing the organism and eliminating other causes. Tetracycline, trimethoprim / sulphonamide and cephalosporins are usually effective therapies.

Fungal and algal colitis

Histoplasmosis is a dimorphic fungus affecting dogs and cats in the USA. Infection occurs after inhaling the spores from the environment. Some infections result in pulmonary disease but may disseminate to other sites, including the Gl tract. Colonic disease is common in dogs with disseminated disease where the mycotic infection causes extensive granulomatous tissue reaction. Signs vary in affected dogs from mild, chronic large bowel diarrhoea to severe disease causing tenesmus, haematochezia, faecal mucus, feverand weight loss. Diagnosis requires identification of the aetiologi-cal agent in mucosa! biopsy specimens or colorectal cytological samples. Special stains (e.g. Periodic acid-Schiff stain, PAS) may be required to confirm that the organism is present in histological specimens. Therapy usually consists of itraconazole (10 mg/kg p.o. q12-24h) alone or in combination with amphotericin B (0.25-0.5 mg/kg i.v. q48h, up to a total cumulative dose of 5-10 mg/kg in dogs and 4-8 mg/kg in cats). Prognosis depends on disease dissemination but is generally good with long-term (4-6 month) anti-fungal therapy.

Other mycoses affecting the bowel are relatively uncommon. Both Pythium spp. (pythiosis) and several genera of zygomycetes (zygomycosis) may deeply invade digestive tissues causing severe granulomatous gastroenteritis. Pythiosis is most common in young, large-breed dogs that reside in the southern USA. Signs include chronic intractable diarrhoea and vomiting, anorexia, depression and weight loss. Physical examination often reveals an abdominal mass or marked regional thickening of the bowel. Diagnosis depends on histological identification of the organisms in mucosal biopsy samples. Treatment is radical surgical excision of the granulomatous mass since these fungi are resistant to standard antifungal drugs. The prognosis is guarded.

Prothecaspp. are ubiquitous unicellular algae that may rarely colonize the Gl tract of dogs and cats, causing severe ulcerating enterocolitis. Dissemination is common with preferential sites including the eyes, visceral organs and the central nervous system. Diagnosis requires organism identification in affected tissues. There is no effective treatment and the prognosis is poor.

Chronic colitis (inflammatory bowel disease)

IBD broadly refers to a group of idiopathic chronic Gl disorders characterized by infiltration of the Gl tract with inflammatory cells. Recent studies involving animal models of intestinal inflammation have identified interactions between the mucosal immune system, the host genetic susceptibility and environmental factors (e.g. normal resident microflora) as potential factors in disease development. Several pathogenic mechanisms have been proposed for chronicintestihal inflammation including an abnormal immune response to a luminal pathogen or abnormal luminal constituent, or an aberrant mucosal immune response to a normal luminal constituent, such as a dietary or microbial antigen. Clinical signs in affected animals are attributed to the effects of mucosal cellular infiltrates and inflammatory mediators ().

A diagnosis of IBD is one of exclusion and requires ruling out many other diseases that may cause intestinal inflammation. Systemic diseases, chronic parasitism, dietary sensitivity, infectious diseases and alimentary neoplasia are the major differential diagnoses for IBD. Histological evaluation of mucosal biopsy specimens is required for a definitive diagnosis. Unfortunately, no standard microscopic grading system for IBD lesions has been established in dogs or cats. Furthermore, biopsy interpretation is very subjective from one pathologist to the next and is further hampered by avariety of procurement and processing artefacts inherent in evaluation of endoscopic specimens. A definitive histological diagnosis of iBD should be based upon microscopic evidence of mucosal inflammation, which includes:

  • Mucosal glandular loss, necrosis or immaturity
  • Epithelial erosion or ulceration
  • Villous atrophy, fusion or collapse
  • Fibrosis or oedema in the lamina propria.

An objective histological grading scheme for the diagnosis of canine and feline IBD has been proposed and has proven useful in numerous clinical and research investigations. Using this system, histological severity of IBD is determined by the extent of epithelial-glandular alterations rather than subjective evaluation of lamina proprial cellularity. It is noteworthy that increases in mucosal immune cell populations may be a reflection of the normal immunological responses to diverse dietary and microbial stimuli. Changes in mucosal cellularity alone, without other evidence of inflammation or enterocyte injury, should be interpreted cautiously and are unlikely to be IBD. Nevertheless, veterinary pathologists continue to use standard classification schemes, based upon the predominant infiltrating cell type to define chronic colitis in dogs and cats ().

Lymphocytic-plasmacytic colitis: Lymphocytic-plasmacytic colitis (LPC) is the most common form of chronic colitis in the dog and cat. As in most cases of IBD, affected animals are middle-aged or older, and clinical signs are generally cyclical with tenesmus, mucoid faeces and haematochezia predominating. Abnormalities observed during endoscopy may include increased mucosal friability, increased mucosal granularity, loss of submucosal vascularity and erosions. Absence of these observations does not eliminate LPC so biopsy samples should be collected.

Eosinophilic colitis: Eosinophilic colitis (EC) may represent a variant of IBD or may occur as an allergic manifestation to dietary or parasitic antigens. The prevalence of EC is considerably less than that for LPC. As is the case with LPC, middle-aged animals are affected most frequently. Physical examination, including digital examination of rectal mucosa, may detect a roughened irregular mucosa in dogs and cats with EC. Mucosal biopsy samples are required for definitive diagnosis and yield a diffuse infiltration of eosinophils (with perhaps lesser numbers of cell types) within the colonic mucosa. The mucosa will be more friable on endoscopic examination and may be ulcerated as compared with LPC.

Chronic histiocytic ulcerative colitis: Ch ronic histiocytic ulcerative colitis (CHUC) is the least frequently diagnosed IBD variant. Affected dogs present with intractable large bowel diarrhoea, haematochezia or tenesmus of variable severity. Lethargy, anorexia and weight loss are commonly observed. Boxers are predisposed to CHUC and the disease is diagnosed most frequently in male dogs <1 year of age. Histologically, lesions are characterized by a mixed inflammatory infiltrate with PAS-positive histiocytes within the mucosa. Colonoscopy usually reveals increased mucosal granularity, friability and diffuse erosions. The prognosis with this IBD variant is usually very poor. One recent report suggests that clinical signs may resolve with enrofloxacin therapy (rather than traditional immuno-suppressive therapy) indicating either an unidentified infection or a possible causal role for the resident microflorain mediating intestinal inflammation of CHUC.

Dietary treatment: Dietary therapy, while often not curative alone, is extremely important in the long-term management of most diseases of the colon or anorectum. Dietary therapy (Table Commercially available prescription diets for the management of colonic diseases. This list is not intended to be exhaustive but representative of the many commercial products available in Europe and North America) may consist of:

  • Feeding a novel protein (hypoallergenic) diet
  • Feeding a highly digestible diet
  • Feeding a high fibre diet.

Each of these approaches has merits, depending on the clinical situation, but there is no specific way to determine which dietary approach might be successful. A reasonable approach is to feed one of the diets for a period of 3-4 weeks and if no positive response is observed then try a diet from the other categories. The most frequently recommended group of diets for therapy of large bowel disease in dogs and cats are those containing increased amounts of dietary fibre. This strategy is reasonable because dietary fibres, depending on their fermentability, influence luminal SCFA production as well as colonic motility, both of which may have a positive influence on the health and function of the colon ().

Table Commercially available prescription diets for the management of colonic diseases. This list is not intended to be exhaustive but representative of the many commercial products available in Europe and North America

Diet category Commercial canine diets Specifics (protein/carbohydrate/fibre/other)
Hypoallergenic (Novel protein and carbohydrate sources) Hill’s Canine d/d (canned & dry)

Eukanuba Response Formula FP, KO (canned & dry) IVD Canine Limited Ingredient Diets (canned & dry) Royal Canin Waltham Diets Canine Select Protein (canned & dry)

Purina CNM HA Formula/Canine and Purina CNM LA Formula/Canine (dry)

Hill’s canned: whitefish or lamb & rice, dry: egg & rice, duck & rice, salmon & rice

Eukanuba: canned/dry: catfish, nerring meal & potato, kangaroo & oat

IVD: rabbit, venison, lamb, whiteish or duck & potato

Waltham canned: lamb & nee, dry: catfish & nee, capelin & tapioca

Purina HA (dry): modified soy protein & corn starch, LA (dry): salmon meal, trout & rice

Highly digestible (Low fat, low residue) Hill’s Canine i/d (canned & dry)

Eukanuba Low Residue/Canine (dry) (Intestinal Formula)

IVD Canine Neutral Formula (dry), IVD Sensitive Formula (canned & dry)

Royal Canin Waltham Canine Low Fat Diet (canned Sdry)

Purina CNM Canine EN Formula (canned & dry)

Hill’s canned & dry: soy fibre (soluble fibre)

Eukanuba beet pulp fibre (mixed fibre), fructooligosaccharides (FOS), fish oil

IVD Neutral: duck & potato, oat bran and oat hulls fibre, FOS

IVD Sensitive canned: chicken, egg, cottage cheese, oat bran and guar fibre (soluble), FOS: dry: lamb, rice & potato, pea fibre (mixed), FOS

Waltham canned: fish, meat & rice, cellulose powder, guar gum fibre (soluble fibre); dry: cellulose (insoluble fibre), soy protein & rice

Purina canned: beef, rice, egg product, gum arabic, medium chain triglycerides (MCTs) and fish oil; dry: rice & corn, min. fibre, MCTs 8 fish oil

High dietary fibre (Low fat, high fibre) Hill’s Canine w/d (canned & dry)

Hill’s Canine r/d (canned & dry)

IVD Canine Hifactor Formula (canned & dry)

Royal Canin Waltham Canine High Fibre Diet (dry) Purina Canine DCO Formula (dry), Canine OM Formula (canned & dry)

Hill’s w/d canned: cellulose fibre (insoluble fibre); dry: peanut hulls (insoluble fibre)

Hill’s r/d canned: cellulose (insoluble fibre); dry: peanut hulls (insoluble fibre)

IVD canned: cellulose, rice flour & guar fibre (mixed fibre), FOS, fish oil; dry: rice flour, rice hulls (insoluble fibre), FOS, fish oil

Waltham: wheat bran & cellulose (mixed fibre)

Purina DCO dry: beep pulp, pea fibre (mixed), fish oil

Purina OM canned: pea fibre & beet pulp (mixed); dry: cellulose, wheat gluten (mixed)

Diet category Commercial feline diets Specifics (protein/carbohydrate/fibre/other)
Hypoallergenic (Novel protein and carbohydrate sources) Hill’s Feline d/d (canned)

Eukanuba Response Formula LB (canned)

IVD Feline Limited Ingredient Diets (canned & dry)

Royal Canin Waltham Diets Feline Select Protein (canned & dry)

Hill’s canned: lamb & rice

Eukanuba: canned: lamb & barley

IVD: duck, rabbit, venison & iamb 8 green peas

Waltham canned: venison & rice, dry: duck & rice

Highly digestible (Low fat, low residue) Hill’s Feline i/d (canned & dry)

Eukanuba Low Residue/Feline (canned & dry)

IVD Feline Neutral Formula (dry), Purina Feline EN Formula (soft moist)

Hill’s canned & dry: soy fibre (soluble fibre)

Eukanuba beet pulp fibre (mixed fibre), FOS, fish oil

IVD Neutral: duck & potato, beet pulp (sol. fibre), fish oil, FOS

Purina soft: poultry, soybean, fish, vegetable gums, MCTs and fish oil

High dietary fibre (Low fat, high fibre) Hill’s Feline w/d (canned & dry)

Hill’s Feline r/d (canned & dry)

IVD Feline Hifactor Formula (canned & dry)

Royal Canin Waltham Feline Calorie Control Diet (moist & dry)

Feline OM Formula (canned & dry)

Hill’s w/d canned & dry: cellulose fibre (insoluble fibre)

Hill’s r/d canned & dry: cellulose (insoluble fibre)

IVD canned: cellulose & guar fibre (mixed fibre), FOS, fish oil; dry:

poultry by products, corn & rice, pea fibre, beet pulp (mixed fibre), FOS, fish oil

Waltham: moist: guar gum (soluble), cellulose, dry: cellulose (insoluble fibre)

Purina OM canned: pea fibre 8 oaf fibre (mixed); dry: soybean hulls (insoluble)

There is ample and increasing evidence that feeding dogs with colitis diets with increased amounts of dietary fibre is beneficial. The question remains, however, as to which fibre type is most appropriate. Dietary trials with either a hypoallergenic diet (e.g. novel protein source) or a highly digestible diet (Table Commercially available prescription diets for the management of colonic diseases. This list is not intended to be exhaustive but representative of the many commercial products available in Europe and North America) are prudent due to the role of dietary sensitivity or intolerance in the development of intestinal inflammation. However, most dogs or cats with food hypersensitivity or intolerance have primarily small bowel signs (e.g. vomiting, anorexia, weight loss, and sometimes chronic diarrhoea); thus, signs of large bowel diarrhoea alone are less likely to be due to allergic disease. Feeding patients with colonic disease highly digestible diets would be expected to be beneficial because less ingesta reaches the colon resulting in the production of a smaller faecal mass. This can be especially important in colonic disorders where there is severe mucosal disease, in patients with severe constipation or obstipation where motility is altered or absent, or in recto-anal diseases where minimal production of faeces is desirable. Since long-term dietary management may be required in pets with colonic or recto-anal disease, use of a commercial diet (rather than a home-made diet or a diet supplemented with fibre) is often the best approach. However, adding one or two tablespoons per 25 kg bodyweight of psyllium, pumpkin or other mixed fibres () to the animal’s regular diet is another way of increasing the dietary fibre content.

Medical treatment: There are several drug treatment options for the management of colitis in dogs and cats where reducing inflammation is the primary means of controlling the clinical disease (). One approach in dogs is to use non-steroidal anti-inflammatory drugs (NSAIDs) such as sulfasaiazine. 5-Aminosalicylic acid (5-ASA) is the active moiety and its mechanism of action is its anti-leucotriene activity and free radical scavenging ability. Newer aminosalicylic acid drugs (e.g. mesalazine) preparations are available that allow delivery of 5-ASA without the sulphur moiety, which is believed to be responsible for the numerous adverse effects (e.g. keratoconjunctivitis, vomiting) associated with sulfasalazine use. These newer products include oral delayed release preparations of 5-ASA that prevent its absorption in the upper Gl tract, and products that have an azo bond like sulfasalazine, but the sulphur component is replaced with another amine (balsalazide) or a second 5-ASA (olsaiazine). Sulfasalazine and olsalazine are the most common products used in dogs with colitis and have established dosages ().

The use of these drugs in cats is not recommended due to their increased sensitivity to NSAlDs and increased potential for toxicity. Therapy of all cats (and many dogs) with colitis often requires use of anti-inflammatory or immunosuppressive doses of corticosteroids. Long-term (months) and high dose (>2 mg/kg/day) corticosteroid therapy may be associated with side-effects that limit its use or require alternative therapy choices. Generally, oral prednisolone or methylprednisolone is the preferred corticosteroid for use in both dogs and cats rather than dexamethasone, betamethasone or triamcinolone. In humans, efforts to reduce the corticosteroid side-effects include using rectal suppositories or enemas containing corticosteroids, or use of other newer glucocorticosteroid preparations, which cause fewer systemic side-effects (e.g. budesonide). Budesonide has been used in limited numbers of dogs and cats with IBD and there are a few reports of effectiveness. However, controlled trials using this drug have not been published. The addition of immunosuppressive drugs to the medical therapy protocol is required to manage severe or refractory cases of colitis. The drugs used most commonly are azathioprine or chlorambucil, but ciclosporin is also another therapeutic option (). Therapy with these drugs can be associated with significant side-effects. Thus, appropriate monitoring and adjustment of the drug dose is recommended. In dogs or cats with severe colitis, combination therapy, using corticosteroids, immunosuppressive drugs, NSAIDs or enemas may be required to achieve adequate control. This has been especially true in Boxer dogs with histiocytic ulcerative colitis, one of the most severe IBD variants.

Antibiotics effective against anaerobic bacteria (amoxiciliin, ampicillin, tylosin, clindamycin or metronidazole) are often effective in reducing bacteria) overgrowth and potential enterotoxin production. Resolution of clinical signs usually occurs following 3-5 days of antibiotic therapy in dogs or cats with acute disease. Alternatively, in animals with chronic colitis, long-term therapy with metronidazole is required to maintain clinical remission. The actions of metronidazole may be attributable to its direct inhibition of cell-mediated immunity or its antimicrobial effect on phlogistic resident microflora.

Disorders affecting colonic motility

Intussusception: Both ileocolic and caecocolic intussusceptions may occur in dogs and cats, with the former being more common. Lesions may develop secondary to other disease (e.g. parvovirus enteritis, whipworm infestation) but the cause in many cases is unknown. Acute intussusception in the dog classically causes scant bloody diarrhoea, vomiting and abdominal pain. Most affected cats do not have diarrhoea. Chronic intussusceptions may cause diarrhoea without mucus, haematochezia,vomiting or abdominal pain. Abdominal palpation may reveal a mass or a markedly thickened loop of bowel. Occasionally, intussusceptions may ‘slide’ in and out making palpation unreliable. Survey radiography is seldom diagnostic. Ultrasonography will confirm the presence of the classic ‘target’ lesion if present in animals with ‘sliding’ or ‘intermittent’ intussception. Colonoscopy may find the telescoped intestine within the colonic lumen. Therapy involves either reduction or resection of the intussusception.

Irritable bowel syndrome: Irritable bowel syndrome (IBS) is defined as an uncommon, non-inflammatory large bowel disease associated with abnormal colonic myoelectrical function. Clinical signs are characterized by chronic intermittent large bowel diarrhoea (tenesmus, faecal mucus and/or haematochezia), which is most often seen in large-breed dogs. A diagnosis of IBS is one of exclusion, made only by normal colonoscopic biopsy results and ruling out other causes such as dietary, parasitic, infectious and chronic (IBD) colitis. The primary treatment consists of supplementing dietary fibre (e.g. psyllium, 1-3 tablespoon per meal) to correct abnormal motility patterns. Patients that fail to respond to dietary management alone may benefit from motility modifying drugs, such as loperamide.

Constipation: Constipation denotes infrequent or difficult evacuation of faeces and is commonly observed in both dogs and cats. Prolonged and severe faecai impaction may result in irreversible megacolon which fails to respond to medical management. Constipation is particularly common in middle-aged and older cats and is associated with diverse aetiologies (). It is noteworthy that most cases of feline constipation are attributable to idiopathic megacolon. Diagnosis of constipation is made on history, abdominal palpation of faecal impaction, and/or radiographic confirmation of colonic distension. Specific therapy depends on the severity of constipation and the underlying cause. Animals with mild to moderate constipation are treated with a combination of water enemas, dietary fibre supplements, laxatives (e.g. dioctyl sodium sulfosuccinate (DSS), lactulose) and prokinetic (e.g. cisapride) agents (). Colectomy should be considered in animals with severe, refractory constipation or idiopathic megacolon.

Colonic neoplasia: Both malignant and benigntumours affect the colon in dogs and cats. In dogs, adenocarcinoma is diagnosed most frequently followed by lymphosarcoma and leiomyosarcoma. The majority of canine large bowel neoplasms are’located in the descending colon and rectum, although leiomyosarcomas often occur in the caecum. Adenocarcinoma and lymphosarcoma are the most common malignant tumours in cats, followed by mast cell tumours. Malignant feline tumours usually arise in the ileocolic and descending colonic regions. Regional metastasis of adenocarcinoma to the peritoneum and mesenteric lymph nodes occurs in 50% of cats.

Most malignant tumours occur in older dogs and cats. Clinical signs are often indistinguishable from other causes of chronic colitis. Physical examination in animals with malignant colonic tumours may reveal dyschezia, palpable abdominal mass, mesenteric lymphadenopathy, rectal mass or excessive mucosal granularity on digital examination. Imaging (diagnostic radiography and ultrasonography) provides important staging information concerning disease burden. Colonoscopy with mucosal biopsy confirms a definitive diagnosis. Treatment of colonic neoplasia is variable depending on tumour type, location and extent of metastasis. Surgical excision is recommended for focal adenocarcinoma and leiomyosarcoma. Diffuse colonic lymphosarcoma is best treated with multiple drug chemotherapy, such as the Madison-Wisconsin or UW-25 protocols. The long-term prognosis for most malignant neoplasms is guarded. Surgical resection or endoscopic polypectomy is recommended in dogs with benign (adenomatous) polyps and carries an excellent prognosis.

Table Aetiology of constipation

Aetiology Cause
Dietary Low residue diet

Excess fibre

Ingested foreign material e.g. bones, hair

accumulation

Environmental Inactivity (obesity, hospitalization)

Change in routine

Unsanitary living conditions

Painful defecation Dyschezia ()
Colonic obstruction Extraluminal:

Enlarged prostate

Old pelvic fracture Intraluminai:

Stricture, tumour or foreign body

Perineal hernia/rectal diverticulum

Neuromuscular Megacolon

Lumbosacral spinal cord disease

Fluid or electrolyte imbalance Dehydration

Hypokalaemia

Hypercalcaemia

Drug-induced Anticholiriergics; phenottwines; opiates

Laxative abuse