Gastrointestinal Tract Diseases in Companion Animals

Oral Diseases

Oral diseases include various conditions affecting the mouth. Gingivitis/Periodontal Disease is caused by plaque, anaerobic bacteria, and inflammation, manifesting as gingival inflammation, hyperplasia, periodontitis, and loose teeth. Treatment primarily involves good dental care. Lip Fold Pyoderma results from constant moisture in lip folds, leading to bacterial growth, and presents with irritation and odor. Oral Trauma can be caused by fights, foreign bodies (FBs), chemical burns, or falls. A Salivary Mucocele is an accumulation of saliva in subcutaneous (SQ) tissue, appearing as a slowly growing, non-painful swelling with stringy fluid on tap, and is treated by surgical drainage. Oral Neoplasia can be benign, such as papillomas and epulides, or malignant, including squamous cell carcinomas, malignant melanomas, and osteosarcomas; malignant forms are typically locally invasive but usually do not spread to the lungs.

Esophageal Diseases

Esophagitis / Gastroesophageal Reflux can be caused by chemical irritants or physical trauma. Treatment involves avoiding induced vomiting, administering activated charcoal, sucralfate, acid reducers, and antibiotics (Abx), with a Gastrostomy tube ($G$-tube) potentially required. For Esophageal Foreign Bodies, treatment involves endoscopic removal or pushing the foreign body into the stomach for a gastrotomy.

Gastric Diseases

Acute Gastritis presents with anorexia, vomiting, and possibly dehydration or pain. Treatment involves nothing per os (NPO), SQ or IV fluids, antiemetics, and a low-fat bland diet. Inflammatory Bowel Disease (IBD) involves the accumulation of inflammatory cells in the GI tract lining, is more common in cats, and causes chronic vomiting, weight loss (wt loss), and diarrhea. Diagnosis requires ruling out other causes and intestinal biopsies, with treatment involving immunosuppressive drugs and a hypoallergenic diet. Gastric Ulceration is caused by Non-Steroidal Anti-Inflammatory Drugs (NSAIDs), steroids, or stress, leading to anorexia, vomiting, black tarry stools, anemia, and abdominal pain. Diagnosis is through endoscopy or possibly barium series, treated with omeprazole. Gastric Dilatation Volvulus (GDV) is characterized by pain, restlessness, bloat, depression, unproductive vomiting, increased Heart Rate (HR), and increased Respiratory Rate (RR). Diagnosis is confirmed with a right lateral radiograph, and treatment includes a $G$-tube for gas relief, IV fluids, and surgery. Prevention measures include small frequent meals and limiting exercise after eating. The mortality rate is $15-18$, and gastropexy does not guarantee against future dilation. Gastric Neoplasia, most commonly adenocarcinoma, presents with nonspecific clinical signs like weight loss, anorexia, and vomiting. Diagnosis is via endoscopy, and treatment is surgical, though often the tumors are inoperable.

Small Intestine Diseases

Diarrhea is the most common problem affecting the small intestine, with acute cases managed by supportive and symptomatic treatment. Parvovirus is diagnosed via ELISA testing and a low White Blood Cell (WBC) count, treated with IV fluids (avoiding SQ fluids) and keeping the patient warm. Mortality is $50\%$ in canines, and the prognosis is poor in cats. Intestinal Lymphangiectasia is a chronic protein-losing intestinal disease due to impaired lymphatic drainage, causing edema, ascites, and weight loss. Diagnosis involves a Complete Blood Count (CBC) showing lymphopenia and decreased albumin and globulin levels, treated with prednisone and metronidazole to decrease protein loss. Intestinal Neoplasia, including adenocarcinomas and lymphosarcomas, presents with progressive signs related to tumor growth and potential partial obstruction. Diagnosis involves abdominal palpation, barium studies, and endoscopy, with lab tests possibly showing anemia, hypoproteinemia, and leukocytosis with a left shift. Treatment is surgical if possible.

Large Bowel Diseases

The large bowel's primary function is water and electrolyte absorption. Clinical signs of large bowel disease include diarrhea, straining to defecate, and blood in the stool, diagnosed typically by colonoscopy. Inflammatory Bowel Disease (IBD) - Colonic involves colonic inflammation, leading to decreased sodium and water absorption and increased motility, treated with sulfasalazine, prednisone, and metronidazole. Intussusception is the telescoping of bowel segments, causing partial to complete obstruction and compromised blood supply, often due to parasitic infection, FBs, infections, or neoplasia. Clinical signs include vomiting, diarrhea, anorexia, and depression, diagnosed by palpation and ultrasound, and treated with surgery (Resection and Anastomosis (R&A)). Megacolon, common in obese cats, causes straining to defecate, and possibly vomiting and anorexia; owners may mistake liquid stool passing around hard stool for diarrhea. Diagnosis is by palpation and radiographs, treated with enemas and deobstipation. Prevention includes lactulose or Miralax, Propulsid, increased dietary fiber, and increased water intake, with subtotal colectomy as a surgical option. Constipation (Canine) involves straining without passing stool, potentially accompanied by anorexia or vomiting, caused by FBs, tumors, pelvic injuries, anal sac abscesses, or urinary tract obstruction. Diagnosis is through palpation, radiographs, and rectal palpation.

Liver Disease

Drug or Toxin-Induced Liver Disease can be caused by substances such as acetaminophen, NSAIDs, phenobarbital, antifungals, anabolic steroids, halothane, and methoxyflurane. Acute clinical signs include anorexia, vomiting, diarrhea/constipation, possible jaundice, and depression. Diagnosis involves history, palpation, chemistry screen (showing increased liver enzymes, decreased glucose, increased ammonia, coagulopathy), radiographs, ultrasound, and biopsy. Acute treatment is supportive care, nutritional support, and N-acetylcysteine (for acetaminophen). Chronic clinical signs include weight loss, anorexia, ascites, jaundice, Polydipsia and Polyuria (PU/PD). Chronic diagnosis involves history, bloodwork, and liver biopsy, with treatment focusing on a low protein diet, hydration, lactulose (if neurologic signs), and antibiotics. Canine Infectious Hepatitis is uncommon due to vaccination programs. Leptospirosis is a zoonotic disease causing acute renal failure, possibly liver failure, dehydration, vomiting, fever, PU/PD, and jaundice. Diagnosis is via titers showing a $4$-fold increase, treated with penicillin and doxycycline. Precautions include isolation, protective clothing, and good hygiene. Cholangiohepatitis (Cats) is caused by ascending biliary infection from the GI tract, possibly immune-mediated, with Persian cats predisposed. Clinical signs include anorexia, depression, weight loss, vomiting, dehydration, fever, and jaundice, treated with antibiotics, fluids, and nutritional support. Feline Hepatic Lipidosis, often seen in obese cats following stressful events and anorexia, involves excessive lipid accumulation in hepatocytes. Clinical signs include anorexia, weight loss, depression, icterus, and possible hepatopathy. Diagnosis involves CBC, chemistry screen, radiographs, ultrasound, and liver biopsy or Fine Needle Aspiration (FNA), with treatment focused on maintaining and encouraging eating. Liver Neoplasia, encompassing primary and metastatic tumors, presents with vague clinical signs such as anorexia, lethargy, weight loss, PU/PD, vomiting, jaundice, possible diarrhea or bleeding, and anemia or hepatomegaly. Bloodwork may show anemia, hyperbilirubinemia, hypoalbuminemia, and hypoglycemia, with a guarded to poor prognosis. A Portosystemic Shunt (PSS) is a vascular shunt bypassing the liver that fails to close at birth, leading to unneutralized GI toxins. Clinical signs include vomiting, diarrhea, stunted growth, and neurological signs (head pressing, circling, ataxia, depression) that worsen after high-protein meals, treated surgically.

Pancreatic Dysfunction

Pancreatitis involves the activation of digestive enzymes within the pancreas, leading to autodigestion, often caused by drugs or fatty meals. Clinical signs include vomiting, diarrhea, fever, and abdominal pain (right cranial quadrant). Diagnosis is through Pancreatic Lipase Immunoreactivity (PLI), with treatment involving NPO, symptomatic fluids, and antibiotics; peritonitis is a risk. Schnauzers are predisposed, and cats often present with a triad disease (pancreatitis, cholangiohepatitis, IBD). Exocrine Pancreatic Insufficiency (EPI) is an inadequate production of digestive enzymes, predominant in young German Shepherds. Pathophysiology involves a lack of normal food digestion and absorption, leading to bacterial overgrowth. Clinical signs include weight loss (despite good appetite), flatulence, and grayish, foul-smelling diarrhea, treated with supplementation of digestive enzymes.

Recto-anal Disease

Perineal Hernias predispose intact male dogs over $8$ years old, caused by neurogenic atrophy of the levator ani muscle, leading to outpouching of the rectum and other pelvic organs. Treatment involves stool softeners, surgery, and neutering. Perianal Fistulas present as single or multiple ulcerated sinuses, causing pain, bleeding, and self-mutilation, treated with cyclosporin. Perianal Adenomas are firm masses on the anal ring (single or multiple) occurring in older intact male dogs, problematic if ulcerated, and treated with neutering and/or surgery.