Graves' Hyperthyroidism

Thyroid-stimulating immunoglobulins (TSI), also called TRAb (TSH-receptor antibodies), are IgG autoantibodies that bind the extracellular domain of the TSH receptor on thyroid follicular cells. Unlike most autoantibodies that destroy targets, TSI mimic TSH and continuously activate Gs-coupled signaling → cAMP rises → thyroid hormone synthesis and follicular hyperplasia accelerate. The receptor is also expressed on retro-orbital fibroblasts and pretibial fibroblasts, which is why Graves' uniquely causes ophthalmopathy and pretibial myxedema — same antibody, multiple targets. TSI levels often correlate with disease severity and ophthalmopathy activity, and persistent TSI predicts relapse after antithyroid drug withdrawal.

First confirm hyperthyroidism: suppressed TSH (<0.01 mIU/L) with elevated free T4 and/or free T3. Then determine the cause. Three approaches: (1) TSH-receptor antibody (TRAb or TSI) — positive in 95-99% of Graves'; this is increasingly the first-line diagnostic since it's blood-based and definitive. (2) Radioactive iodine uptake (RAIU) at 24 hours — >35% indicates Graves' or toxic nodular disease; uptake pattern on scan differentiates diffuse (Graves') from focal (toxic adenoma) or low uptake (thyroiditis, exogenous). (3) Doppler ultrasound — increased vascularity (thyroid inferno) supports Graves'. Diffuse goiter, ophthalmopathy, and family history of autoimmune disease add clinical confidence.

All three are effective; choice depends on patient factors and preferences. Methimazole (5-30 mg/day, blocks TPO and iodine organification): first-line in most countries, ~50% remission after 12-18 months, risk of agranulocytosis (~0.3%) and hepatotoxicity. PTU reserved for first trimester pregnancy and thyroid storm. Radioactive iodine (I-131, single oral dose ~10-15 mCi): definitive ablation, ~90% rendered euthyroid or hypothyroid; avoid in pregnancy, breastfeeding, severe ophthalmopathy. Thyroidectomy: rapid cure, preferred for large goiters with compressive symptoms, severe ophthalmopathy, pregnancy after first trimester if drugs fail, suspected malignancy. Lifelong levothyroxine after RAI or surgery.

Graves' orbitopathy affects ~25-50% of patients clinically, ~70% on imaging. TSH-receptor antibodies bind retro-orbital fibroblasts, triggering IGF-1 receptor cross-activation, hyaluronan deposition, and lymphocytic infiltration of extraocular muscles and orbital fat. The orbit becomes a fixed-volume box being filled with edematous tissue, pushing the globe forward (proptosis/exophthalmos). Symptoms: dry gritty eyes, retro-orbital pain, diplopia, lid retraction, lid lag, in severe cases optic nerve compression with vision loss. Smoking dramatically worsens it. Mild: artificial tears, selenium. Moderate-severe active: IV methylprednisolone, teprotumumab (IGF-1R blocker), orbital radiation. Inactive sequelae: orbital decompression, strabismus, eyelid surgery.

Thyroid storm is decompensated hyperthyroidism — extreme tachycardia (often >140), hyperthermia (>38.5°C), CNS dysfunction (agitation, delirium, seizure, coma), GI symptoms, and high-output heart failure. Triggered by surgery, infection, RAI, iodine load, parturition, or untreated severe disease. Burch-Wartofsky score ≥45 confirms. Mortality 10-30%. Treatment is multi-pronged and immediate: propranolol (block β-adrenergic and conversion of T4 to T3), high-dose PTU (preferred over methimazole — also blocks peripheral conversion), Lugol's iodine 1 hour after PTU (Wolff-Chaikoff effect to shut down hormone release), hydrocortisone (block conversion and treat possible adrenal insufficiency), cooling, treat the trigger. ICU monitoring.

Female-to-male ratio is approximately 7-10:1, similar to other autoimmune diseases. Estrogen promotes type 2 immunity and humoral (antibody) responses. X-linked genes that escape X-inactivation (TLR7, FOXP3, CD40L) raise effective dose in XX vs XY. Microchimerism — fetal cells persisting in maternal tissue after pregnancy — may seed autoimmune attack. Pregnancy and postpartum periods are common trigger times. HLA-DR3 and CTLA-4 polymorphisms confer risk. Smoking, stress, and iodine excess (e.g., amiodarone, iodinated contrast) can precipitate disease in genetically susceptible individuals.

Diagnosis in pregnancy is tricky — hCG cross-stimulates TSH receptor in first trimester, transiently suppressing TSH (gestational thyrotoxicosis), usually mild and self-limited. True Graves' may improve in second/third trimesters as immune tolerance increases. Treatment: PTU in first trimester (methimazole linked to aplasia cutis and choanal atresia), switch to methimazole after 16 weeks (PTU hepatotoxicity risk). Target free T4 in upper-normal range to avoid fetal hypothyroidism. TRAb crosses placenta — high maternal titers can cause neonatal Graves'. Postpartum: Graves' often relapses or flares; postpartum thyroiditis (transient) is separate and far more common.