NEWS
When disease attacks the liver
Posted: Saturday, June 08, 2002
Several diseases and plants can cause failure of the body's hepatic system
The liver is a remarkable organ with tremendous regenerative powers, and, while problems are common in horses, most cases do not result in liver failure. Some conditions do cause liver failure, however, and those are the ones we will discuss.
The liver is the largest organ in the horse's body, weighing between ten and 20 pounds, and it is the body's chemical-processing plant. It manufactures bile and processes digested proteins, sugars, minerals, and other food products. When it becomes diseased, the body's entire nutritional system is endangered.
Diagnostic procedures can be used to determine the condition of the liver.
Certain enzyme levels in the blood elevate when liver damage occurs. The one enzyme that is the most liver-specific is sorbitol dehydrogenase (SDH). The other enzymes are also affected by disorders of other body parts or systems and thus do not give as much information in most cases as does SDH.
Ultrasound is used in determining such liver problems as hepatomegaly (enlarged liver), hepatic fibrosis, bile-duct dilatation, bile stones, tumors, and abscesses, as well as an aid in determining the site of a biopsy.
Following are the more common causes of liver failure.
Theiler's disease
Also known as serum hepatitis, Theiler's disease is the subacute death of liver tissue and may result in acute encephalopathy as well as liver failure. It is called serum hepatitis because it frequently follows the administration of tetanus antitoxin one to three months earlier.
The usual signs are central nervous system disorder (anywhere from mild circling to maniacal behavior), jaundice, and dark urine. An affected horse may be blind. Diagnosis is based on the signs, history of tetanus-antitoxin administration within the previous three months, and elevated SDH, which lowers quickly if the horse is able to recover.
A liver biopsy is the only way to make a definitive diagnosis, but if the history, signs, and laboratory findings are there, a biopsy is not needed.
There is no specific treatment for Theiler's disease other than supportive therapy and avoidance of stress. Intravenous fluids are helpful, and Xylazine (Rompun) may be used to control the horse's actions. Ammonia production in the gastrointestinal tract should be reduced by the administration of neomycin. For the same reason, low-protein feed and grass hay should be fed until recovery has occurred.
Hyperlipemia
Hyperlipemia is a problem primarily of overweight ponies and donkeys, but it may occur in fat horses as well. Occasionally, it occurs in late pregnancy. Its name means too much fat, specifically in the blood. The signs are acute anorexia (not eating), depression, and edema of the lower abdomen. The plasma is whitish due to high amounts of lipid, but liver-function tests are usually within normal limits.
Treatment consists of fluids and addressing the horse's nutritional needs. The prognosis for an animal completely off feed is poor, but even in one still eating, it is guarded.
Cholangiohepatitis
Cholangiohepatitis is a great word, but one that I have never had to use-until now. What it means is the bile duct is blocked by a chololith (gallstone). The condition is probably caused by an ascending biliary-tract infection. Clinical signs include fever, liver enlargement that may cause colic, and biliary obstruction that produces jaundice and photosensitization. The horse usually goes off feed, and weight loss occurs.
Diagnosis is based on the signs and laboratory findings. The enzyme gamma glutamyl transaminopeptidase (GGT) is markedly elevated, as are bile acids. The bilirubin level will be increased if the horse is jaundiced. An ultrasound examination will show an enlarged liver and bile-duct distension. Also, stones may be seen, but they are not visible in about half the cases. A biopsy will help to confirm the diagnosis and will allow a culture to be done to identify whatever microorganism is present.
In cases of cholangiohepatitis without stones, the prognosis is good. In those cases with stones or with severe hepatic fibrosis, there is only a fair to poor prognosis.
Tyzzer's disease
Tyzzer's disease is an uncommon disorder of foals one to six weeks of age caused by Bacillus piliformis. The usual sign is a dead foal.
In foals that have not succumbed to the disorder, fever, depression, convulsions, and diarrhea are present. The foal may be unable to stand up.
The diagnosis is based on signs and age. Treatment is unsuccessful, and the prognosis is about as bad as it comes.
Plant toxins
Several plants adversely affect the liver. The first is Ragwort. This condition formally is known as pyrrolizidine alkaloid toxicosis, and ragwort is only one of several plants that contain the alkaloid. Others include groundsel, tarweed, rattlebox, and comfrey. One type of plant or another grows all over the United States, Canada, and the world.
The signs include weight loss, altered behavior, jaundice, depression, ataxia, and head pressing. Because the condition tends to be chronic, diagnosis is a challenge. SDH may have returned to normal levels before signs are seen, but GGT will be elevated when the signs are present. A biopsy is necessary to differentiate this from other causes of liver damage. A continued elevation of GGT indicates a poor prognosis, and treatment is unsuccessful in most cases.
The best treatment is prevention; eliminate the plants from the diet.
Other plants that adversely affect the liver are kleingrass (Southwest), fall panicum (East), and alsike clover (Northeast). The signs for all three are the same: depression, jaundice, weight loss, and photosensitivity.
Diagnosis is made from a history of ingesting the plants and the incidence of more than one affected horse on a farm or in an area. GGT is elevated. To treat, remove both affected and unaffected horses from the fields containing the plants or stop feeding hay with the plants in it. Supportive therapy is necessary.
Other toxins
Other toxins include mycotoxin (moldy corn poisoning). The most common liver-damaging mycotoxin is Fusarium, a mold often found in corn. Encephalitic signs are more common than signs of liver involvement. Treatment consists of supportive therapy and luck; affected horses usually will not make it.
Another is iron toxicosis. Iron ingested or injected in excess can lead to liver damage, although it is uncommon. When liver damage does occur, treatment is usually ineffective. The prognosis is poor.
Bile-duct obstruction
Bile-duct obstruction associated with gastrointestinal disease may occur in young foals with ulcers. The foal is jaundiced, has slightly elevated GGT, shows signs of ulcers, and has a large amount of gastric reflux. Surgery is needed to correct the problem, but the prognosis is poor. In adult horses, this may occur in cases of colon displacement, such as torsion. Surgery is necessary.
There are a few other causes of liver damage leading to liver failure, but they are rare. Those listed above are the most common, and even they are not seen often.
Brent Kelley, D.V.M., is a practicing veterinarian living in Paris, Kentucky.
