21 - Equine Thyroid dz

Question 1

(Goiter)

1. most common cause in horses?

2-3. what two conditions can affect thyroid dysfx?

Answer 1

1. benign thyroid adenoma (normal fx)
2. thyroid neoplasia (hyperT possible but usually not)
3. iodine def or excess (hypoT possible)

Question 2

(Dx)

1. usually measure what?
2. why do we rarely measure response of T3/T4 to stim?

Answer 2

1. total and free T3 and T4 (limited testing of TRH, TSH)
2. $$$, mult samples

Question 3

(hyperthyroidism - rare)

1. only get when?
2. Dx?
3. Tx?

Answer 3

1. with neoplasia
2. ^ total and free thryoid hormones
3. partial or complete throidectomy

Question 4

(Hypothyroidism - extremely uncommon)

1. overdiagnosed in horses - why?

Answer 4

1. low [Th] more likely side effect of non-thyroidal illness syndrome -> still ahve normal thyroid fx

Question 5

(non-thyroidial illness syndrome)

1. what is it?
2. physiological signif?

Answer 5

1. transient/reversible hypoT related to stress, illness, or systemic inflam
2. no evidence of adverse fx

Question 6

(Fetal/Congenital HypoT)

1. what causes this?
2. Cx?
3. Dx?
4. tx?
5. prog?

Answer 6

1. dam’s diet has too much/too little iodine, or ^ nitrates (goitrogens)
2. abortion, dysmaturity, cuboidal dz, mandibular prognathism, poorly developed pectoral musc, +/- goiter
3. assess dam’s diet (most important)

assess thyroid fx (may be normal by birth)

4. correct mare nutrition, thyroid supplements (rarely work)
5. poor

Question 7

(IT/Metabolic syndrome)

1. why give thyroid hormones?
2. what drug do we use?

best use of this?

Answer 7

1. induce hyperT -> ^ wt loss, ^ insulin sens
2. levothyroxine

short term mgmt of severe EMS most common rational use