Chronic Enteritis

Chronic enteritis is a persistent inflammatory condition of the small intestine lasting for more than three weeks, characterized by clinical signs such as chronic diarrhea, vomiting, weight loss, and malabsorption. It encompasses a spectrum of disorders including inflammatory bowel disease (IBD), food-responsive enteropathy, antibiotic-responsive enteropathy, and protein-losing enteropathy. The inflammation can be lymphocytic-plasmacytic, eosinophilic, granulomatous, or neutrophilic, and may involve the duodenum, jejunum, and ileum. Chronic enteritis disrupts the normal absorptive and barrier functions of the intestinal mucosa, leading to nutrient malabsorption, protein loss, and altered gut motility. The condition is often progressive and may be associated with systemic complications such as hypoalbuminemia, vitamin deficiencies, and secondary bacterial overgrowth.

The etiology of chronic enteritis is multifactorial and often idiopathic. Primary causes include dietary antigens (food-responsive enteropathy), intestinal dysbiosis (antibiotic-responsive enteropathy), genetic predisposition (e.g., certain breeds like German Shepherds, Yorkshire Terriers, and Soft-Coated Wheaten Terriers), and immune dysregulation. Infectious agents such as Giardia, Tritrichomonas foetus, Salmonella, Campylobacter, and Clostridium perfringens can trigger or exacerbate chronic inflammation. In some cases, chronic enteritis may be secondary to exocrine pancreatic insufficiency, intestinal lymphoma, or other neoplastic conditions. Environmental factors, including stress, poor husbandry, and concurrent diseases, may also contribute. The exact molecular triggers involve aberrant T-cell responses, cytokine imbalances (e.g., increased TNF-alpha, IL-2, IL-6), and loss of tolerance to commensal bacteria and dietary proteins.

Chronic enteritis is a common cause of chronic gastrointestinal signs in dogs and cats. It can occur at any age but is more frequently diagnosed in middle-aged to older animals. Certain breeds are overrepresented: in dogs, German Shepherds, Yorkshire Terriers, Soft-Coated Wheaten Terriers, and Boxers; in cats, Siamese and other purebreds. There is no strong sex predilection. The incidence is higher in animals with a history of acute gastroenteritis, dietary indiscretion, or chronic stress. Geographic variations may reflect differences in infectious agents and dietary practices. In referral populations, IBD is diagnosed in up to 30% of dogs with chronic vomiting and diarrhea.

The pathophysiology of chronic enteritis involves a complex interplay of genetic susceptibility, mucosal immune dysregulation, and environmental triggers. The intestinal epithelium normally acts as a barrier, but in chronic enteritis, tight junction integrity is compromised, leading to increased permeability and antigen uptake. This triggers an exaggerated immune response, with infiltration of inflammatory cells (lymphocytes, plasma cells, eosinophils, or neutrophils) into the lamina propria and epithelium. Pro-inflammatory cytokines (e.g., TNF-alpha, IL-1, IL-6) are upregulated, while anti-inflammatory cytokines (e.g., IL-10) are downregulated. This leads to tissue damage, villous atrophy, crypt hyperplasia, and fibrosis over time. Malabsorption results from reduced absorptive surface area and enzyme deficiencies. Protein-losing enteropathy occurs when lymphatic obstruction or severe inflammation causes loss of proteins into the gut lumen. Secondary bacterial overgrowth and dysbiosis further perpetuate inflammation. Systemic effects include hypoalbuminemia, electrolyte imbalances, and activation of the acute-phase response.

Predisposing factors for chronic enteritis include genetic susceptibility (e.g., certain MHC haplotypes), breed-specific risk (e.g., German Shepherds for IBD, Soft-Coated Wheaten Terriers for protein-losing enteropathy), and age (middle-aged to older animals). Dietary factors such as high-fat diets, food allergies, or intolerance to specific proteins or carbohydrates are common triggers. Chronic stress, overcrowding, and poor sanitation can increase susceptibility to infectious agents. Concurrent diseases such as exocrine pancreatic insufficiency, chronic pancreatitis, or intestinal lymphoma can predispose to or mimic chronic enteritis. Immunosuppressive therapy (e.g., corticosteroids) may alter the mucosal immune response. Additionally, previous antibiotic use can disrupt the normal gut microbiota, leading to dysbiosis and inflammation.

Clinical signs of chronic enteritis are typically chronic and intermittent, lasting for weeks to months. The most common signs include chronic diarrhea (small bowel diarrhea characterized by large volume, watery, or steatorrheic feces), vomiting, weight loss, and decreased appetite. Some animals may have increased appetite (polyphagia) due to malabsorption. Abdominal discomfort, borborygmus, and flatulence are often reported. In severe cases, signs of protein-losing enteropathy may be present, including peripheral edema, ascites, and pleural effusion. Physical examination may reveal poor body condition, muscle wasting, pale mucous membranes, and thickened bowel loops on abdominal palpation. In cats, chronic enteritis may present with chronic vomiting and weight loss, with diarrhea being less prominent. Systemic signs such as lethargy and fever may occur if there is secondary bacterial translocation or concurrent inflammation.

Differential diagnoses for chronic enteritis include: 1) Food-responsive enteropathy (dietary trial responsive), 2) Antibiotic-responsive enteropathy (dysbiosis), 3) Exocrine pancreatic insufficiency (EPI) – characterized by chronic diarrhea, weight loss, and low serum trypsin-like immunoreactivity (TLI), 4) Intestinal lymphoma – especially in cats and older dogs, may require histopathology and immunophenotyping, 5) Protein-losing enteropathy (e.g., lymphangiectasia) – often associated with hypoalbuminemia and panhypoproteinemia, 6) Chronic pancreatitis – may cause vomiting and abdominal pain, with elevated pancreatic lipase immunoreactivity (PLI), 7) Parasitic infections (e.g., giardiasis, trichomoniasis) – diagnosed by fecal examination or PCR, 8) Inflammatory bowel disease (IBD) – confirmed by intestinal biopsy, 9) Bacterial overgrowth (e.g., small intestinal bacterial overgrowth – SIBO) – diagnosed by quantitative culture or response to antibiotics, 10) Intestinal neoplasia (e.g., adenocarcinoma, leiomyosarcoma) – may require imaging and biopsy. Key distinguishing features include response to dietary modification, response to antibiotics, serum TLI and PLI levels, and histopathological findings.

The diagnostic approach to chronic enteritis should be systematic. Step 1: Perform a thorough history and physical examination, including body condition scoring and abdominal palpation. Step 2: Run baseline laboratory tests: complete blood count (CBC), serum biochemistry profile, urinalysis, and fecal examination (direct smear, flotation, and Giardia antigen test). Step 3: Measure serum folate and cobalamin (B12) levels to assess small intestinal function and bacterial overgrowth. Step 4: Consider serum TLI and PLI to rule out EPI and pancreatitis. Step 5: Perform abdominal imaging (radiographs and ultrasound) to assess bowel wall thickness, lymphadenopathy, and other abnormalities. Step 6: If no specific cause is found, initiate a dietary trial with a novel protein or hydrolyzed diet for 2-4 weeks. If there is partial or no response, consider an antibiotic trial (e.g., tylosin or metronidazole) for 2-4 weeks. Step 7: If still non-responsive, perform upper GI endoscopy with intestinal biopsies (duodenum and ileum) and/or full-thickness surgical biopsies. Step 8: Histopathology will confirm the type of inflammatory infiltrate and rule out neoplasia. Step 9: Additional tests such as fecal PCR panels for infectious agents, serum cPLI/fPLI, and measurement of acute-phase proteins (e.g., CRP) may be helpful in selected cases.

Hematology: CBC may show mild anemia (non-regenerative) due to chronic inflammation or blood loss, and eosinophilia in cases of eosinophilic enteritis. Serum biochemistry: Hypoalbuminemia is common in protein-losing enteropathy; globulins may be normal or decreased. Liver enzymes (ALT, ALP) may be mildly elevated due to hepatic lipidosis or concurrent inflammation. Electrolyte imbalances (hypokalemia, hyponatremia) can occur due to diarrhea. Blood gas analysis may reveal metabolic acidosis. Urinalysis: Usually unremarkable, but urine protein:creatinine ratio (UPC) may be elevated if there is concurrent protein-losing nephropathy. Specific biomarkers: Serum cobalamin (B12) may be low due to ileal disease or bacterial overgrowth; folate may be low (proximal disease) or high (bacterial overgrowth). Pancreatic lipase immunoreactivity (PLI) is normal in chronic enteritis unless concurrent pancreatitis. C-reactive protein (CRP) may be elevated in inflammatory conditions. Serology/PCR: Fecal PCR panels for Giardia, Tritrichomonas, Salmonella, Campylobacter, and Clostridium perfringens can identify infectious triggers. In cats, feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) testing may be indicated.

Radiography: Abdominal radiographs may show gas-filled bowel loops, but are often unremarkable. Ultrasonography: This is the most useful imaging modality. Findings include thickening of the muscularis and mucosal layers, loss of normal layering, hyperechoic mucosal striations, and mesenteric lymphadenopathy. Doppler ultrasound can assess blood flow. In cases of lymphangiectasia, hyperechoic mucosal striations may be seen. Computed Tomography (CT): CT enterography may provide detailed assessment of bowel wall thickness and lymph nodes, but is less commonly used. Magnetic Resonance Imaging (MRI): MRI is not routinely used for intestinal disease but may be helpful in evaluating perianal fistulas. Endoscopy: Upper GI endoscopy allows direct visualization of the duodenal mucosa, which may appear erythematous, friable, or nodular. Endoscopic biopsies can be obtained. Fluoroscopy: Barium contrast studies can assess motility and mucosal patterns, but are less sensitive than ultrasound.

Cytology: Fine-needle aspiration of mesenteric lymph nodes may reveal reactive hyperplasia or neoplasia. Intestinal cytology via endoscopic brushing is not commonly performed. Histopathology: Intestinal biopsies are the gold standard for diagnosis. Findings include infiltration of the lamina propria with lymphocytes and plasma cells (lymphocytic-plasmacytic enteritis), eosinophils (eosinophilic enteritis), or neutrophils (neutrophilic enteritis). Villous blunting, crypt hyperplasia, and fibrosis may be present. In protein-losing enteropathy, dilation of lacteals (lymphangiectasia) is seen. Special stains (e.g., Gram stain) may identify bacterial overgrowth. Immunohistochemistry can differentiate T-cell vs. B-cell infiltrates and help rule out lymphoma.

Treatment of chronic enteritis is multimodal and tailored to the underlying cause. For food-responsive enteropathy, a strict dietary trial with a novel protein or hydrolyzed diet is essential. For antibiotic-responsive enteropathy, a trial of tylosin (10-20 mg/kg PO q12h) or metronidazole (10-15 mg/kg PO q12h) for 2-4 weeks is recommended. For IBD, immunosuppressive therapy is often required: prednisolone (dogs: 1-2 mg/kg PO q12h, tapering over weeks; cats: 1-2 mg/kg PO q12h) or budesonide (dogs: 1-3 mg/dog PO q24h; cats: 1 mg/cat PO q24h) for refractory cases. Additional immunosuppressants include cyclosporine (5 mg/kg PO q24h) or azathioprine (dogs: 2 mg/kg PO q24h; cats: 0.3 mg/kg PO q48h). Supportive care includes fluid therapy for dehydration, antiemetics (e.g., maropitant 1 mg/kg SC q24h), and antidiarrheals (e.g., loperamide 0.1 mg/kg PO q8h) if needed. Nutritional support with a highly digestible, low-fat diet is crucial. In severe protein-losing enteropathy, parenteral nutrition may be required. Surgical intervention is rarely needed but may be indicated for obstructive lesions or to obtain full-thickness biopsies.

The prognosis for chronic enteritis varies depending on the underlying cause and response to therapy. Food-responsive enteropathy has an excellent prognosis with dietary management. Antibiotic-responsive enteropathy also has a good prognosis, though relapse may occur. IBD is a chronic condition that often requires long-term immunosuppression; many animals achieve remission, but relapses are common. Protein-losing enteropathy carries a guarded prognosis, especially if severe hypoalbuminemia (<2.0 g/dL) is present. Negative prognostic indicators include marked weight loss, severe hypoalbuminemia, presence of ascites or pleural effusion, and lack of response to initial therapy. The overall mortality rate is low, but some animals may require lifelong management.

Follow-up is essential to monitor response to therapy and adjust medications. Re-check examinations should be performed every 2-4 weeks initially, then every 3-6 months once stable. Serial monitoring includes body weight, body condition score, serum albumin, cobalamin, and folate levels. Repeat abdominal ultrasound may be indicated to assess bowel wall thickness and lymphadenopathy. For animals on immunosuppressive therapy, regular CBC and biochemistry profiles are needed to monitor for adverse effects. Tapering of corticosteroids should be gradual over weeks to months. Long-term management may involve dietary modifications and periodic antibiotic or immunosuppressive therapy. Owners should be educated on recognizing signs of relapse and the importance of compliance.

Pearls: 1) Always rule out exocrine pancreatic insufficiency with serum TLI before assuming IBD, as EPI can mimic chronic enteritis. 2) A dietary trial should be strict and last at least 2-4 weeks; ensure no other food sources are given. 3) Cobalamin supplementation is often necessary in chronic enteritis; administer 250-500 mcg SC weekly for 6 weeks, then monthly. 4) In cats, chronic vomiting may be the only sign of IBD; consider intestinal biopsy early. 5) Use budesonide as a steroid-sparing agent with fewer systemic side effects. Pitfalls: 1) Do not use corticosteroids before ruling out infectious causes, as they can worsen infections. 2) Avoid using metronidazole as a sole therapy for IBD; it is not as effective as corticosteroids. 3) Do not rely on fecal flotation alone to rule out Giardia; use antigen testing or PCR. 4) Do not perform intestinal biopsies if the patient has severe hypoalbuminemia without first stabilizing with albumin or plasma transfusions. 5) Do not discontinue immunosuppressive therapy abruptly; taper gradually to avoid rebound inflammation.

Based on Plumb's Veterinary Drug Handbook, the following protocols are recommended: 1) Prednisolone: Dogs: 1-2 mg/kg PO q12h for 2-4 weeks, then taper by 25% every 2-4 weeks to the lowest effective dose. Cats: 1-2 mg/kg PO q12h, taper similarly. 2) Budesonide: Dogs: 1-3 mg/dog PO q24h; Cats: 1 mg/cat PO q24h. 3) Cyclosporine: Dogs: 5 mg/kg PO q24h; Cats: 5 mg/kg PO q24h. Monitor trough levels if possible. 4) Azathioprine: Dogs: 2 mg/kg PO q24h; Cats: 0.3 mg/kg PO q48h. Use with caution in cats due to potential myelosuppression. 5) Tylosin: 10-20 mg/kg PO q12h for 2-4 weeks. 6) Metronidazole: 10-15 mg/kg PO q12h for 2-4 weeks. 7) Maropitant: 1 mg/kg SC q24h for vomiting. 8) Cobalamin: 250-500 mcg SC weekly for 6 weeks, then monthly. 9) Fluid therapy: Balanced crystalloids (e.g., LRS) at maintenance rates (60-100 ml/kg/day) with potassium supplementation as needed. 10) For protein-losing enteropathy, consider human albumin (250 mg/kg IV over 4-6 hours) or plasma transfusions. Adjust dosages in renal or hepatic impairment; avoid NSAIDs and other ulcerogenic drugs.

Key studies and consensus guidelines: 1) ACVIM consensus statement on the diagnosis and treatment of chronic inflammatory enteropathy in dogs and cats (2010) emphasizes a stepwise approach including dietary trials, antibiotic trials, and immunosuppressive therapy. 2) A study by Allenspach et al. (2007) found that hypoalbuminemia and severe histologic lesions are negative prognostic indicators in canine IBD. 3) A randomized controlled trial by Craven et al. (2004) showed that budesonide is as effective as prednisolone with fewer side effects in canine IBD. 4) A study by Jergens et al. (2010) demonstrated that a combination of prednisolone and cyclosporine is effective in refractory cases. 5) The WSAVA Gastrointestinal Standardization Group (2010) provided guidelines for histopathologic evaluation of intestinal biopsies. 6) A meta-analysis by Kathrani et al. (2011) identified breed-specific risk factors for IBD in dogs. 7) Recent research on the gut microbiome (e.g., Suchodolski et al., 2012) highlights the role of dysbiosis in chronic enteritis and the potential for fecal microbiota transplantation as a novel therapy.