Disorders of the Thyroid Gland (TV4101, Lecture 3 Notes)

List the roles of thyroid hormone

List the aetiologies of canine hypothyroidism

Congenital = non-proportional dwarfism

Secondary and tertiary = low TSH and T4/T3

Discuss the stages of thyroiditis

i.e. assessment of anti-thyroglobulin is redundant

List dermatologic signs of hypothyroidism

- Endocrine alopecia symmetric/asymmetric with areas of friction/pressure and rat tail

- Dry brittle hair coat

- Hyperpigmentation

- Seborrhea

- Pyoderma

- Otitis externa

- Myxedema

List additional signs of hypothyroidism

- Lethargy

- Mental dullness

- Inactivity

- Weight gain

- Vestibular disease

- Facial nerve paralysis

- Esophageal hypomotility

- Diarrhea or constipation

List CBC and biochemistry findings of hypothyroidism

CBC

- Mild normocytic normochromic nonregenerative anaemia

Biochemistry

- Fasting hypercholesterolemia

- Fasting hypertriglyceridemia

- Hyponatremia (myxedema coma)

- Mild increase in muscle enzymes

Describe total T4 endocrine tests

- Anti-T3/T4 Ab interfere with assay

- Relatively robust and reliable test

Describe free T4 endocrine tests

- Remains normal in non-thyroidal illness

- Assess with equilibrium dialysis (more sensitive and specific)

Describe thyrotropin (cTSH) endocrine tests

Discuss euthyroid sick syndrome

- Adaptive response to inflammatory cytokines (i.e. nonthyroidal illness)

- Decreased TSH secretion with decreased T4 and T3 response

- Glucocorticoids inhibit TSH secretion, sulfonamides block iodination of thyroglobulin and phenobarbital causes low T4/T3 with increased TSH

- Assess CRP levels (i.e. inflammatory marker)

- Treatment with thyroid hormone not recommended

Discuss the interpretation of endocrine tests for hypothyroidism

Discuss the treatment of hypothyroidism

0.02mg/kg BID Levothyroxine (synthetic T4), reassess 6-8 weeks later 4-6hrs post pill.