Endocrine

Question 1

What are the parts of the anterior pituitary gland?

Answer 1

Pars distalis and pars tuberalis

Question 2

Where is the pars intermedia located?

Answer 2

Between the anterior and posterior parts

Question 3

Describe the physiology of the pituitary gland

Answer 3

Stress -> hypothalamus releases CRH and vasopressin -> pituitary secretes ACTH -> adrenals secrete cortisol

Question 4

What type of feedback loop does cortisol have on the pituitary and hypothalamus?

Answer 4

Negative feedback loop

Question 5

What is the main type of cell in the pars intermedia?

Answer 5

Melanotropes

Question 6

What disorder in humans has similar lesions to PPID in horses?

Answer 6

Parkinson’s disease

Question 7

How does dopamine normally influence pituitary hormones?

Answer 7

Interacts with melanotropes to inhibit ACTH and alpha-MSH which control cortisol release

Question 8

How is dopamine different in PPID horses?

Answer 8

Oxidative neurodegeneration damages dopaminergic hypothalamic neurons. This leads to the loss of inhibitory tone in pars intermedia (increased ACTH production)

Question 9

What are clinical signs of PPID?

Answer 9

Hypertrichosis, chronic or intermittent lameness, sole abscesses, PU/PD, sweating, muscle wasting, lethargy, recurrent infections, abnormal fat deposits, inappropriate lactation, blindness, seizures

Question 10

What clinicopathologic changes are associated with PPID?

Answer 10

Hyperglycemia, hyperinsulinemia, hypertriglyceridemia, increased liver enzymes, increased ACTH (consistent but not always active). Sometimes anemia, neutrophilia, lymphopenia, high fecal egg count.

Question 11

How is PPID diagnosed?

Answer 11

Clinical signs, age, endogenous ACTH concentration (consider seasonal RR- higher in the fall), response to therapy, necropsy

Question 12

What is the gold standard for PPID diagnosis?

Answer 12

Stimulation test. Grain fasted then administer 1mg TRH IV, draw sample in EDTA tubes 10 min later, submit plasma for ACTH measurement. Recommended to do in the spring.

Question 13

Would you expect ACTH to be high or low for a horse with PPID?

Answer 13

High

Question 14

How is PPID treated?

Answer 14

Pergolide (dopaminergic agonist, can reduce appetite), cyproheptadine (serotonin agonist, can be added on), management (deworming, manage laminitis, hair-trims, adequate nutrition)

Question 15

What are the 3 main components of equine metabolic syndrome?

Answer 15

Obesity, insulin dysregulation, and laminitis

Question 16

What is the common signalment for equine metabolic syndrome?

Answer 16

Likely susceptible from birth, 5-10 years old at presentation, described as “easy keepers”

Question 17

What clinical signs are associated with equine metabolic syndrome?

Answer 17

Laminitis, obesity, regional adiposity (cresty neck, around tail head, behind shoulder, prepuce or mammary gland), “easy keeper”

Question 18

How is equine metabolic syndrome diagnosed?

Answer 18

Based on signalment, clinical signs, diagnosis of insulin resistance (IV glucose tolerance test or combined glucose insulin tolerance test)

Question 19

Describe the combined glucose insulin test

Answer 19

Grain fast overnight, obtain baseline glucose and insulin, administer dextrose IV then insulin IV, then check BG at intervals. If insulin >100uU/mL at 45 min- resistant

Question 20

What insulin concentration measurement is consistent with hyperinsulinemia?

Answer 20

> 50uU/mL

Question 21

What result on an insulin tolerance test is consistent with insulin resistance?

Answer 21

<50% decrease in BG from baseline 30 mins after insulin administration

Question 22

How is equine metabolic syndrome managed?

Answer 22

Restrict/eliminate grazing, don’t feed grain, provide mineral/vitamin/protein ration balancer, add daily exercise (unless laminitis present). Levothyroxine can be used to increase metabolic rate, activity level, and insulin sensitivity. Metformin hydrochloride can be used to increase insulin sensitivity.

Question 23

How does adult hypothyroidism occur in horses?

Answer 23

VERY RARE- from exogenous compounds, pituitary disorders, iodine deficiency or excess, or neoplasia

Question 24

What clinical signs are consistent with adult hypothyroidism?

Answer 24

Lethargy, poor performance, obesity, laminitis, cresty neck, EMS or PPID

Question 25

What are signs of surgically thyroidectomized horses?

Answer 25

Lethargy, poor performance, decreased body temperature, decreased appetite, scaly hair, anemia, low heart rate, respiratory signs

Question 26

How is hypothyroidism diagnosed?

Answer 26

Serum levels of T3 and T4 (increased TSH, decreased T3 and T4)

Question 27

How should T3 and T4 react to TSH or TRH administration?

Answer 27

T3 should double at 2 hours, T4 should double at 4 hours

Question 28

How is hypothyroidism treated in adult horses?

Answer 28

Daily iodine intake 1-5mg, levothyroxine supplementation 20ug/kg

Question 29

Describe congenital goiter

Answer 29

Thyroid enlargement causing inadequate or excessive iodine intake by mare. Causes stillbirths, prematurity, hypothermia, weakness, and physeal dysgenesis. Prognosis poor.

Question 30

Describe congenital hypothyroidism and dysmaturity syndrome in foals

Answer 30

Causes increased gestational length but dysmature foals, weak at birth, hypothermic, musculoskeletal problems, thyroid glands histologically hyperplastic w/ small follicles and minimal colloid. Baseline thyroid hormones can be low or normal but TSH response is always decreased. Prognosis guarded.