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Hepatic Encephalopathy in Dogs

By: Dr. Arnold Plotnick

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Hepatic encephalopathy is a neuropsychiatric disorder that occurs in animals and people with advanced liver disease. In dogs, it is most often seen when blood is diverted or shunted around the liver, called portosystemic shunting. Blood can be diverted around the liver because of a congenital shunt present at birth or an acquired shunt that occurs secondary to long-term liver disease.

HE is often manifested as a wide range of neurologic abnormalities. The first signs are usually behavioral. At first, the changes are subtle, and they may wax and wane. As the disorder progresses, the signs become more obvious. Signs may be precipitated by a meal. As the syndrome becomes more apparent, dogs usually has a few bad days, alternating with days in which the dog is acting fairly normal.

While any severe liver disease can lead to HE, portosystemic shunts are the most likely disorder to produce signs of HE; approximately 95 percent of animals with portosystemic shunts show signs of HE. In decreasing order of frequency, these signs are:

  • Depression
  • Personality changes
  • Drooling
  • Stupor
  • Pacing or circling
  • Staggering or incoordination
  • Blindness
  • Collapse or weakness
  • Seizures
  • Head pressing
  • Hyperactivity
  • Head or muscle tremors
  • Deafness
  • Coma

    There are several theories as to what actually causes the neurologic signs that are seen when the liver is not able to function properly. However, ammonia has always been implicated as one of the important toxins that contribute to neurologic signs. The liver converts ammonia into urea. When the liver is too diseased to do this properly, or if blood containing high levels of ammonia bypasses the liver because of a shunt, the ammonia circulates in high levels in the blood stream, and this affects the brain, causing the neurologic signs described.

    A grading system has been modified from human medicine, for use in animals. In this system animals with HE are graded on a scale of 1 to 4.

  • Grade 1. Animal shows listlessness, depression, mental dullness, personality changes, excessive urination.

  • Grade 2. Animal shows incoordination, disorientation, compulsive pacing or circling, head pressing, apparent blindness, personality changes, salivation and excessive urination.

  • Grade 3. Stupor, severe salivation and seizures, although uncommon, are present.

  • Grade 4. Coma

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