A few notes that I’ve collected on thyroid topics. All are basics and tips that makes studying the subject much easier (IMO).

BASICS
• TSH normal = euthyroid patient
• Hypo/hyperthrodism is NOT related to gland size; rather, to -/+ of thyroid hormones
• Goiter = enlargement of the thyroid gland due to any cause

THYROID-RELATED SUBSTANCES
• TRH; from hypothalamus, stim. TSH rel.
• TSH; from ant. pituitary, stim. T3/T4 rel.
• TBG; a-globulin, binds to T4 mainly, to T3 less firmly
• TSI (B-lymphocyte-derived); stim. TSH receptors, found in Graves dse
• TG; precursor of T3/T4, used in assessment of thyroid cancer
• Anti-TG Abs; aka AMA; elevated in Hashimoto thyroiditis

Thyroid function tests (TFTs)
• Radioactive iodine uptake/scan; useful in thyrotoxic states, but not in hypothyroid st.
• Total T4/T3; not accurate, affected by TBG which flactuates. There could be + TBG, not + T4 production, giving + total T4
• Free T4; is the preferred test to directly assess the thyroid H.
• T3 resin uptake (T3RU); same idea of total iron binding capacity (TIBC); used in conj. with total T4 test
if low = + TBG, – T4
if high = – TBG, + T4
• TSH;
if normal = euthyroid (definitive)
if low = hyperthyroid (mostly)
if high = hypothyroid (mostly)

¶ To differentiate a 1ry thyroid dse from a 2ry one (pituitary or hypoth.):
:: TSH amount is INVERSELY prop. to THs in 1ry thyroid dse (THs decrease/increase » TSH increases/decreases)
:: TSH amount is DIRECTLY prop. to THs in 2ry th. dse (TSH increases/decreases » THs increase/decrease)

P.S. You can also apply this rule on other hormone couples like cortisone/ACTH.

THYROIDITIS
• Any thyroiditis causes ++ ESR, fever
• Graves dse; autoimmune dse (TSI), B-lymphocytic infiltration of thyroid gl./eyes/skin
• Ophthalmopathy in hyperthyroid dses is almost exclusive to Graves dse
• Hashimoto thyroiditis is also an autoimmune dse (Anti-TG Abs), painless goiter in mid-aged women, TFTs usually normal, ttt L-thyroxine
• Subacute thyroiditis; viral, tender, self-limited
• Both HT & SAT present by hyperthyroidism that progresses to hypoth.

NODULES
• Malignant nodule is usually; solid, fixed, solitary, rapidly-growing, nontender, cold (radionuclide scan) with hoarseness/dyphagia, history of neck irradiation
• US/Fine needle aspiration for any nodule;
benign » thyroxine
malignant » surgery