How Liver Disease Affects Dogs
The liver executes some of the most complex and vital functions in a dog’s body. It metabolizes fats, carbohydrates and proteins and is involved in the production of essential blood clotting factors. It synthesizes a number of key enzymes and helps remove ammonia from the bloodstream. The liver also stores vitamins and minerals and aids in the digestion and detoxification of circulating wastes, drugs and poisons.
The clinical signs of liver disease (medically referred to as “hepatobiliary disease”) are extremely variable due to the liver’s extensive interaction with other organs and its unusual regenerative capacity. More than one-half (and maybe up to 70 or 80 percent) of functional liver tissue must be destroyed before liver failure can be diagnosed.
Symptoms of Liver Disease in Dogs
Some dogs show no clinical manifestations of liver damage, especially in the very early stages of disease. Once symptoms do develop, they usually are nonspecific. The severity of any given symptoms does not necessarily correlate with the severity or extent of liver damage, or with the animal’s prognosis. Because the liver is intimately involved in so many essential bodily functions, what appear to be symptoms of liver disease might actually be caused by an abnormality in another organ or organ system. With this in mind, the general signs and physical examination findings often associated with liver disease, irrespective of its cause, include one or more of the following:
- Loss of appetite (inappetence; anorexia)
- Weight loss
- Vomiting (often intermittent but usually chronic)
- Disinterest in normal activities (apathy)
- Diarrhea (less common than vomiting)
- Increased thirst/water intake (polydipsia)
- Increased frequency of urination (pollakiuria)
- Increased volume of urine output (polyuria)
- Unkempt hair coat
- Abdominal enlargement or distention (bloated appearance)
The distended abdomen is usually caused by an enlarged liver or spleen (“organomegaly,” which means an enlarged organ, or more specifically “hepatomegaly” or “splenomegaly”). It also is commonly caused by a build up of fluid in the space between abdominal organs (“effusion” or “ascites”) or by poor abdominal muscle tone (“muscular hypotonia”).
Some more specific signs of liver disease include:
- Jaundice (yellow staining of the serum, skin and mucous membranes caused by build-up of the bile pigment, bilirubin, in circulation. Also referred to as “icterus,” jaundice can turn a dog’s urine a bright, yellowish-orange color (bilirubinuria). It also frequently causes a yellow appearance to the whites of the eyes and mucous membranes of the tongue and gums.)
- Abnormal fecal color and consistency (acholic feces – or changes in fecal color – are caused by an absence of bile pigments in the intestinal tract due to abnormal retention in the blood, which makes the dog’s stools pale and putty-colored. This normally indicates complete bile duct obstruction associated with liver disease.)
- Spontaneous bleeding disorders (animals with liver disease often have problems with coagulation, or clotting, of their blood, called “coagulopathies”. In dogs, the upper gastrointestinal tract – usually the stomach and duodenum, which is the first part of the small intestine - is most commonly affected by coagulation disorders associated with liver disease. This leads to gastrointestinal bleeding/hemorrhage, which owners may detect by seeing blood in their dogs’ stools. Affected dogs may also vomit blood and/or have visible blood in their urine.)
- Blood in the feces (hematochezia)
- Blood in the urine (hematuria)
- Blood in the vomitus (hematemesis)
- Neurological and behavioral changes
Neurological and behavioral changes in dogs with late-stage liver disease are common. They are caused by high levels of circulating toxins that normally are removed by a healthy liver, but not by a diseased one. When these toxins accumulate in the brain, the dog develops a condition called hepatic encephalopathy, (“hepatic” means emanating from or pertaining to the liver). This often leads to:
- Trembling (tremors)
- Lack of coordination (ataxia)
- Aimless wandering
- Mental dullness
- Excessive salivation (drooling)
- Generalized seizures
These signs develop in dogs (and cats) with liver disease, because the cerebral cortex of the brain is exposed to intestinal toxins that normally are removed by a healthy liver but escape hepatic detoxification in cases of liver disease. Most gastrointestinal toxins are derived from normal bacterial metabolism - or digestion - of proteins and their byproducts. Ammonia is one of the most common intestinal toxins contributing to the symptoms of hepatic encephalopathy, which can wax and wane over time. Hepatic encephalopathy tends to be a chronic condition which cannot be cured, but often can be controlled.
Dogs with advanced liver disease can develop a debilitating skin disorder referred to as hepatocutaneous syndrome. The reason for this condition is not well-understood, but its symptoms may appear before signs of internal liver disease are apparent and include:
- Sores/lesions on the footpads (thickened, crusted, ulcerated)
- Foot pain
- Reluctance to rise, walk, exercise or play
- Itchiness (pruritis) of the feet
- Redness between the toes (interdigital erythema)
- Sores/lesions on the ear flaps, external genitalia, oral cavity, eyes, elbows, lower abdomen or elsewhere
Dogs at Increased Risk
Most forms of liver disease are more common in middle-aged to older animals. However, congenital disorders, such as portosystemic shunts and congenital vascular disease, are more frequently seen in young dogs. Acquired copper storage disorders are more common in Bedlington Terriers, West Highland White Terriers, Skye Terriers, Keeshonds, Labrador Retrievers and Dalmatians. Breeds predisposed to chronic hepatitis include the Doberman Pinscher (mainly seen in females), Cocker Spaniel (males are overrepresented), Labrador Retriever, Standard Poodle and Scottish Terrier. Exposure to hepatotoxins is more frequent in free roaming dogs with access to chemicals, heavy metals, stagnant standing water, pesticides, poisonous plants or drugs. Free roaming dogs are also more likely to suffer acute blunt trauma to their liver. Healthy dogs exposed to dogs that have leptospirosis, canine infectious hepatitis or canine adenovirus infection have a greater risk of developing those diseases, which contribute to liver damage.
Only a skilled veterinary professional can assess a dog and perform the tests needed to confirm a diagnosis of liver disease.