The recent diet change in this dog could explain the findings of decreased appetite and weight loss since the new senior diet would probably have less calories than the adult diet and less fat content which might decrease palatability. However, the laboratory abnormalities are not explained by diet change alone.
Inflammatory bowel disease is a collective term used to describe a group of disorders that are characterized by persistent or recurrent GI signs and with histologic evidence of inflammation on biopsy. Causes of chronic small bowel inflammation include: parasitic infections such as Giardia; pathogenic bacteria such as some Salmonella and E. coli species; food allergy; lymphoma; lymphangectasia; lymphocytic-plasmacytic enteritis; and eosinophilic gastroenterocolitis. In this case there is a recent diet change that might support a food allergy as an underlying cause. The dog is also older, so neoplasia cannot be ruled out based on the current information.
Pancreatitis can be classified as acute or chronic. The acute form is usually severe and the chronic form is usually mild. Long standing chronic pancreatitis can be associated with fibrosis and atrophy of the pancreas. The inciting cause of pancreatitis in the dog is usually unknown. More than 50 drugs have been reported to induce pancreatitis in humans. Those commonly used in veterinary medicine include potassium bromide, furosemide, sulfonamides and azathioprine. High fat, low protein diets have also been implicated. Obstructions to pancreatic duct flow may cause reflux of pancreatic fluids and inflammation. The obstruction may be due to IBD, trauma or neoplasia. In this case the dog was somewhat uncomfortable on abdominal palpation and there is a mild increase in the WBC; however, the neutrophils are not increased which would be more commonly seen with pancreatitis.
Heartworm disease may cause very mild clinical signs including decreased appetite and mild weight loss. In this case the presence of an eosinophilia is supportive of heartworm disease. If heartworm disease is more advanced with cardiovascular compromise and circulating inflammatory mediators this could cause intermittent vomiting and glomerulonephritis which could potentially elevate BUN.
The upper urinary tract is most commonly infected by ascending microbes rather than through hematogenous spread. Because blood must pass through the glomerular capillaries in the renal cortex before reaching the medulla, most hematogenous bacteria do not reach the renal medulla and the renal pelvis. Urinary tract obstruction or trauma increases the risk of hematogenous seeding of the urinary tract by interfering with the renal microcirculation. Metabolic diseases such as diabetes mellitus and hyperadrenocorticism also predispose dogs to urinary tract infections.
Urine specific gravity is usually decreased below 1.020 in pyelonephritis and the presence of casts are noted. In this case there are rare and occasional RBC’s and WBC’s, however no casts are apparent and the urine specific gravity is 1.025.
Hyperadrenocorticism is commonly seen in older small breed dogs. Over production of cortisol by the adrenal gland due to a primary pituitary microadenoma is the most common cause in small breed dogs. Dogs typically present for PU/PD and poor hair coats with a pot-bellied appearance. The elevated ALP in this case is supportive of the induction of ALP secondary to increased circulating cortisol. The urine specific gravity is a little high for a typical Cushing’s patient.
Typical hypoadrenocorticism results from decreased production of glucocorticoid and mineralocorticoid hormones from the adrenal glands. These cases typically show signs of inappetance, vomiting, diarrhea, weakness, weight-loss and collapse. Typical laboratory abnormalities include hyperkalemia, hyponatremia, azotemia, mild metabolic acidosis and a normal leukogram.
In contrast atypical Addison’s cases may show no electrolyte abnormalities or changes in only one parameter. Clinical signs are similar but not as pronounced. A definitive diagnosis is made by demonstrating a poor response to ACTH. Young to middle-aged female dogs are most commonly affected. Dogs are treated as for typical Addison’s with prednisone, florinef or DOCP.