Panagiotis G. Xenoulis,     College Station, Texas

Causes of Canine Hyperlipidemia

Table 58-1 presents a list of causes of canine hyperlipidemia (Xenoulis and Steiner, 2010). Postprandial hyperlipidemia is physiologic and typically resolves within 7 to 12 hours after a meal. Therefore determination of serum lipid concentrations should always follow a fast of at least 12 and ideally 15 hours.

Persistent fasting hyperlipidemia is abnormal and can be either primary or secondary to other conditions, diseases, or drug administration. Secondary hyperlipidemia is the most common pathologic form of hyperlipidemia in dogs. Most often, canine hyperlipidemia is the result of obesity or an endocrine disorder such as hypothyroidism, diabetes mellitus, or hyperadrenocorticism. Protein-losing nephropathy and cholestasis are relatively common causes of hypercholesterolemia. Hyperlipidemia has also been traditionally thought to be the result of naturally occurring pancreatitis in dogs, although this has not been convincingly shown.

Primary lipid abnormalities are usually, but not always, associated with certain breeds (see Table 58-1). Depending on the breed, the prevalence of a primary lipid abnormality can vary widely. Also, the geographic region of the canine population tested seems to play an important role due to genetic differences. Primary hyperlipidemia is very common in miniature schnauzers in the United States (with >30% of this breed being affected based on one study) and it was the first breed-related primary lipid disorder described in dogs. It is typically characterized by hypertriglyceridemia; hypercholesterolemia may also be present, but it is not found in all affected miniature schnauzers and is always present in association with hypertriglyceridemia. Primary hyperlipidemia has also been reported to occur in other dog breeds (see Table 58-1).

Clinical Importance of Hyperlipidemia in Dogs

Although hyperlipidemia itself does not seem to lead directly to the development of any major clinical signs, it has been shown to be associated with the development of other diseases that are clinically important and potentially life threatening (Table 58-2).

Hyperlipidemia, and more specifically hypertriglyceridemia, has long been suspected as a causative factor of canine pancreatitis (see Chapter 137). Two recent clinical studies, each using a different methodologic approach, provided evidence that hypertriglyceridemia, especially if severe (>800 mg/dl in one study), is a risk factor for and may cause pancreatitis in miniature schnauzers (Xenoulis et al, 2010; Xenoulis et al, 2011b). Therefore, in dogs with severe hypertriglyceridemia and pancreatitis, the first disorder should be considered the cause of the latter rather than vice versa and treatment of pancreatitis in those cases should always include measures to control hypertriglyceridemia.

In a recent study, primary hypertriglyceridemia was found to be associated with increased serum hepatic enzyme activities in clinically healthy miniature schnauzers (Xenoulis et al, 2008). Although in that particular study the cause of the increased serum hepatic enzyme activities was not determined, clinical studies and anecdotal observations suggest that two hepatic disorders are associated with hypertriglyceridemia in dogs: diffuse hepatocellular steatosis and gallbladder mucocele. Hyperlipidemia-associated hepatocellular steatosis (or hepatic lipidosis) has been anecdotally reported and is characterized by hepatocellular accumulation of triglycerides. Gallbladder mucoceles (see Web Chapter 46) have been commonly reported in dog breeds that are predisposed to primary hyperlipidemia (e.g., miniature schnauzers and Shetland sheepdogs). Mature gallbladder mucoceles might lead to biliary obstruction, cholecystitis, or rupture of the gallbladder.

Another potential complication of hypertriglyceridemia in dogs is insulin resistance. Almost 30% of miniature schnauzers with primary hypertriglyceridemia had evidence of insulin resistance in one study (Xenoulis et al, 2011a). This might have an implication on glycemic control in dogs with hypertriglyceridemia and concurrent diabetes mellitus or other diseases that cause insulin resistance.

Finally, several other conditions have been reported or suspected to be consequences of hyperlipidemia in dogs. These include atherosclerosis, ocular disease (e.g., lipemia retinalis, lipemic aqueous, lipid keratopathy, solid intraocular xanthogranuloma), seizures, and cutaneous xanthomata or lipomas.