Icterus in Small Animals and Horses

Question 1

What is another name for icterus?

Answer 1

Jaundice

Question 2

What is “Icterus”?

Answer 2

Yellow discoloration of body tissues caused by increased levels of bilirubin (sclera, mucous membranes, non-pigmented skin)

Question 3

Is Icterus always a sign of pathology in horses? How can you assess if it is a sign of underlying disease?

Answer 3

Yellow discoloration of sclera/MM’s normal finding in 10-15% of horses
Older horses, horses who eat carotenoids (carrots, dandelion)
Assess bilirubin concentration

Question 4

Explain how bilirubin is formed

Answer 4

Biproduct of the breakdown of hemoglobin from aged RBC’s

Question 5

What is the most common cause of icterus in the horse? How does this process occur?

Answer 5

Anorexia
Shortage of ligandin (liver protein responsible for uptake of unconjugated bilirubin into the liver) due to starvation –> Icterus within 12 hrs

Question 6

How do inflammatory mediators affect bilirubin excretion in dogs/cats? How commonly does this cause jaundice?

Answer 6

Mediators of inflammation slow down the process of bilirubin excretion and can cause jaundice (uncommon)

Question 7

What are the common causes of jaundice in dogs/cats?

Answer 7

Pre-hepatic - increased breakdown of RBC’s (hemolytic anemia)
Post-hepatic - biliary obstruction (bile stones, pancreatic carcinoma)
Hepatic - liver disease, toxin overload

Question 8

What is the difference between hematopoeitic vs hepatobiliary jaundice?

Answer 8

Hematopoietic = pre-hepatic (red cell hemolysis), patient ALWAYS anemic (usually regenerative)
Hepatobiliary = post-hepatic/hepatic jaundice - patient not anemic

Question 9

What are causes of hemolytic anemia in dogs and cats? Give examples

Answer 9

Immune mediated (primary vs secondary) - Ex. IMHA
Microangiopathic/Physical turbulence - Ex. DIC, Hemangiosarcoma, splenic torsion
Metabolic - Ex. diabetes mellitus
Congenital - Ex. deficiencies
Infectious - Ex. Babesia
Drugs/Toxins - Ex. garlic/onions

Question 10

What should you look for in the blood to identify a drug/toxic cause for hemolytic anemia?

Answer 10

Heinz bodies - aggregates of denatured, precipitated hemoglobin within erythrocytes that form as hemoglobin with oxidative damage is metabolized

Question 11

What are causes of hemolytic anemia in horses? What is a very important cause of hemolytic anemia in foals?

Answer 11

Infectious - Ex. Babesia, Anaplasmosis
Toxins - Ex. Wild onions, Maple leaf toxicity
Neonatal isoerythrolysis - VERY IMPORTANT in foals
IMHA

Question 12

Does it matter if you define hepatic vs post-hepatic jaundice in dogs/cats? Why or why not?

Answer 12

No - treatment is the same. Usually dogs have a combination of both hepatic and post-hepatic causes which lead to jaundice.

Question 13

Does it matter if you define hepatic vs post-hepatic jaundice in horses? Why or why not?

Answer 13

Yes - treatment for hepatic disease is very different from treatment for post-hepatic diseases in horses

Question 14

Describe the most common causes of hepatic jaundice in dogs

Answer 14

Chronic inflammatory hepatitis
Neoplasia - Ex. lymphoma
Toxic/Infectious hepatitis - Ex. leptospirosis, Adenovirus

Question 15

Describe the most common causes of hepatic jaundice in cats

Answer 15

Cholangitis (cholangiohepatitis)
FIP
Neoplasia
Hepatic lipidosis

Question 16

What is cholangiohepatitis? What are the different types of cholagiohepatitis?

Answer 16

Cats with this disease develop inflammation of their liver and bile ducts (small vessels within the liver)
Acute/Chronic (neutrophilic) - inflammatory (E. coli, Psuedomonas)
Chronic (lymphocytic) - no bacterial cause, immune-mediated, treat with corticosteroids

Question 17

Describe the most common causes of hepatic jaundice in horses

Answer 17

Hepatocellular disease
- Ragwort toxicity
- Theiler’s Disease (viral hepatitis)

Question 18

What are the most common causes of post-hepatic jaundice in dogs/cats?

Answer 18

Toxic/Infectious cholangitis
Pancreatic disease
Infiltrating/Space-occupying biliary lesions/masses
Bile duct rupture/leakage
Intestinal pathology

Question 19

What are the most common causes of post-hepatic jaundice in horses?

Answer 19

Cholangiohepatitis
Choledocholithasis (biliary calculi)

Question 20

What is unique about the biliary system in a horse?

Answer 20

Horses do not have a gallbladder
Bile goes directly from liver into small intestine

Question 21

What are some non-hepatic causes of increased bilirubin?

Answer 21

Fever
Anorexia
Sepsis/Significant inflammation

Question 22

Does increased bilirubin always indicate jaundice? What is the reference range?

Answer 22

No - increased bilirubin occurs well before jaundice
Ref range for bilirubin in dog 15 umol/L but overt jaundice does not occur until 45 umol/L

Question 23

How is the kidney involved in conjugation of bilirubin? How does this differ in dogs vs cats?

Answer 23

The kidney conjugates bilirubin into water soluble substance (urobilinogen) to excrete in the urine
In dogs the renal threshold is low, meaning mild bilirubinuria (2+) can be normal (especially in males)
Cats are deficient in an enzyme necessary for bilirubin conjugation, so it does not happen in the kidney. The renal threshold for bilirubin in cats is very high, meaning that bilirubinuria is ALWAYS significant in cats.

Question 24

How does bilirubinuria occur in horses?

Answer 24

Not well understood
Can occur with colestasis (decreased bile excretion from liver)