Thyroid – hypothyroid and development

Question 1

Thyroglossal duct cyst

Answer 1

Midline of neck
Moves with swallowing

Remove d/t infection risk

Question 2

MC site of ectopic thyroid tissue

Answer 2

Tongue

Question 3

T3 vs T4

Answer 3

T3: binds receptors w/ greater affinity, shorter half life – few hours
More active

T4: more produced, longer half life, converted to T3 peripherally by deiodinase enzymes
Stable 6-9 days once released into blood

Question 4

Thyroxine-binding globulin

Answer 4

Decreased: low protein states (hepatic failure, nephrotic sn)

• low total T3, T4
• free T3 and T4 unchanged

increased in pregnancy, estrogen, OCPs

• elevated T4/T3
• free T3 and T4 unchanged

Question 5

Hypothyroidism

Answer 5

-> elevation of LDL and cholesterol

Cold intolerance
Wt gain
Constipation
Deepening of voice
Menorrhagia
Slowed mental and physical function
Dry skin with coarse, brittle hair
Reflexes w/ slow return phase

Dx: TSH elevated, free T3/T4 confirmation and extent of dz

Causes:
Congenital hypothyroidism
Ab-mediated destruction – Hashimoto thyroiditis
Iodine deficiency or excess
Subacute granulomatous thyroiditis
Radiation tx of hyperthyroidism
Surgical removal of thyroid
Thyroid destruction from neck radiation for other head/neck chancers
Medications: amiodarone, tyrosine kinase inhibitors, lithium
Idiopathic causes

Question 6

Congenital hypothyroidism

Answer 6

Causes:
Complete agenesis, hypoplasia, or ectopic location
Thyroid-releasing enzyme deficiency
Dysfunctional hormone production, transport, or function
TSH resistance
Transfer of anti-thyroid medication or anti-thyroid Ab form mother
Iodine-deficient diet in mother during pregnancy

Clinical features:
Impaired physical growth
Intellectual disability 
Enlarged tongue
Enlarged/distended abdomen

Question 7

Hashimoto thyroiditis

Answer 7

MC cause of hypothyroidism in US
F>M
HLA-DR5, HLA-B5

Autoimmune
Painless goiter

Dx: thyroid hormone, TSH, thyroglobulin or thyroid peroxidase antibodies

Early: euthyroid, positive Ab, normal TH and TSH, asx – enlarged goiter

Inlammation begins – destruction of thyroid follicle cells, transient hypothyroidism – few months

More destruction of thyroid: infiltration of lymphocytes (not much colloid), hormone production declines, hypothyroidism
-shrunken goiter

Histo: resembles LN

Type IV HSR
Increased risk of B cell lymphoma of thyroid gland

Assoc w/:
Addison Dz
DMI
Pernicious anemia
Vitiligo
Sjogrens

Question 8

Subacute (granulomatous, de Quervain) thyroiditis

Answer 8

Early: hyperthyroid
Later: hypothyroid – if develops, most likely permanent

Can be self limited and return to euthyroid state

Granulomatous infiltration

May be triggered w/ viral infecitons (coxsackie virus, echovirus, adenovirus, measles, mumps)

Clinical feature:
Fever, PAINFUL goiter

Tx:
NSAIDs
Corticosteroids
Thyroid hormone replacement for hypothyroidism

Question 9

Riedel’s thyroiditis

Answer 9

Chronic inflammation of the thyroid -> replaced by fibrous tissue

May be hypothyroid or eythyroid
Fixed, hard, rock like painless goiter

Histo: fibrosis, macrophages, eosinophils

May have extension of fibrosis into local structures – airway

Younger

If older w/ rock hard thyroid w/ extension think cancer esp anaplastic carcinoma of thyroid

Question 10

Tx of hypothyroid

Answer 10

Levothyroxine- synthetic analog of T4

• too high -> tachycardia, heat intolerance, tremors, arrhythmias
• elderly more likely to get arrhythmia, start slow to give heart chance to adjust
• QD dosing
• more physiologic and stable

Thiiodothyronine – synthetic analog of T3

• unpredictable when given PO
• controversial mood enhancement