equis - Articles
Blood: idiopathic hyperammonemia
Introduction
- Cause: idiopathic hyperammonemia has been documented as a rare complication of severe GI disease in adult horses, typically those with enterocolitis and/or colic.
- Significantly elevated blood ammonia (>150 mmol/L) in affected horses is not associated with elevations in other standard biochemical markers of liver disease.
- It is theorized that the high blood ammonia occurs due to massive enteric ammonia release associated with the primary GI disease that overwhelms the livers ability to metabolize the ammonia.
- Overgrowth of urease producing bacteria within the colon and cecum have been implicated.
- Signs: acute encephalopathy associated with GI disease.
- Diagnosis: biochemical evaluation, liver function tests, cerebrospinal fluid analysis, fecal microbiological investigation.
- Treatment: analgesia, sedation/tranquilization, fluid therapy,
- Prognosis: very good if horse successfully treated through acute encephalopathic stage; mortality rates highest in first 72 h of treatment.
Presenting signs
- Acute encephalopathy associated with concurrent or pre-existing GI disease.
Acute presentation
- Encephalopathy wide ranging neurologic signs can be seen, including head-pressing, aimless walking, somnia, mania and seizures.
- Blindness Eye: blindness - overview is commonly documented during encephalopathy with this condition.
- Acute gastrointestinal signs colic Abdomen: pain - adult and/or diarrhea
.
Geographic incidence
- Documented in the US and UK, anecdotal reports from other parts of the world.
Age predisposition
- Mature horses.
Public health considerations
- Encephalopathic mature horses are potentially highly dangerous to themselves and people around them.
Cost considerations
- Affected horses need aggressive supportive treatment, hospitalization for control of encephalopathy and intravenous treatment of metabolic abnormalities.
Special risks
- High risk of acute musculoskeletal catastrophe during encephalopathic episodes.
- Rarely need anesthesia but some individuals are extremely colicky and refractory to analgesics.
- Clinicians should be mindful of severe metabolic and acid-base disturbances associated with this condition (metabolic acidosis Acid-base imbalance , hypokalemia, hyperglycemia, hyperammonemia) that make them poor anesthetic candidates.
Pathogenesis
Etiology
- Unknown, but theorized to occur due to massive ammonia production in large intestine that overwhelms the livers ability to detoxify.
- Potential role for urease producing bacteria in enterocolitis cases, egClostridium sordelli.
- Temporally the hyperammonemia and encephalopathy seem to be preceded by GI disease.
Specific
- Pre-existent or concurrent enterocolitis or colic Abdomen: pain - adult .
Pathophysiology
- High blood ammonia of enteric origin causes the neurologic signs.
- Ammonia disrupts normal neuronal and neurotransmitter physiology within the central nervous system, with subsequent behavioral and encephalopathic changes.
- The metabolic status of affected horses (severe metabolic acidemia Acid-base imbalance , dehydration, hypoproteinemia Hypoproteinemia and endotoxemia Endotoxemia: overview ) exacerbates the animal's general condition and complicates therapy.
Timecourse
- Peracute-acute: 6-48 h from onset of GI disease.
Epidemiology
- Sporadic disease, only affecting one horse at a time.
Diagnosis
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Treatment
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Prevention
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Outcomes
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Further Reading
Publications
Refereed papers
- Recent references from PubMed and VetMedResource.
- Unt V E et al (2012) Gastrointestinal hyperammonaemia in a 35-day-old Warmblood cross filly. Equine Vet Educ 24 (8), 387-391 VetMedResource.
- Dunkel B et al (2010) Putative intestinal hyperammonaemia in horses: 36 cases. Equine Vet J 43 (2), 133-140 PubMed.
- Dunkel B (2010) Intestinal hyperammonaemia in horses. Equine Vet Educ 22 (7), 340-345 VetMedResource.
- Desrochers A M, Dallap B L & Wilkins P A (2003) Clostridium sordelli infection as a suspected cause of transient hyperammonemia in an adult horse. J Vet Intern Med 17 (2), 238-241 PubMed.
- Hasel K M, Summers B A & De Lahunta A (1999) Encephalopathy with idiopathic hyperammonaemia and Alzheimer type II astrocytes in equidae. Equine Vet J 31 (6), 478-482 PubMed.
- Peek S F, Divers T J & Jackson C J (1997) Hyperammonaemia associated with encephalopathy and abdominal pain without evidence of liver disease in four mature horses. Equine Vet J 29 (1), 70-74 PubMed.
- Mair T S & Jones R D (1995) Acute encephalopathy and hyperammonaemia in a horse without evidence of liver disease. Vet Rec 137 (25), 642-643 PubMed.