Endocrinology · Thyroid Disorders
The facts most likely to be tested
Graves disease is caused by thyroid-stimulating immunoglobulins (TSI) that bind to and activate the TSH receptor on thyroid follicular cells.
The classic physical exam finding is a diffuse, nontender goiter often accompanied by a thyroid bruit due to increased vascularity.
Ophthalmopathy, specifically exophthalmos and lid lag, is caused by autoimmune-mediated inflammation and glycosaminoglycan deposition in the retro-orbital space.
Pretibial myxedema, characterized by non-pitting, indurated, erythematous plaques on the shins, is a highly specific dermatologic manifestation of Graves disease.
Initial laboratory evaluation reveals suppressed TSH and elevated free T4/T3, while a radioactive iodine uptake (RAIU) scan shows diffuse, increased uptake throughout the gland.
First-line symptomatic management for thyrotoxicosis involves beta-blockers (e.g., propranolol) to control adrenergic symptoms like tachycardia and tremors.
Definitive treatment options include methimazole (preferred in most patients), radioactive iodine ablation, or thyroidectomy.
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A 34-year-old woman presents to the clinic complaining of a 3-month history of palpitations, heat intolerance, and unintentional weight loss despite an increased appetite. Physical examination reveals a fine tremor, tachycardia, and a diffuse, nontender thyroid enlargement. She also exhibits bilateral proptosis and lid lag on downward gaze. Laboratory studies demonstrate a suppressed TSH and elevated free T4.
What is the most likely diagnosis and the underlying pathophysiology?
Graves disease caused by thyroid-stimulating immunoglobulins (TSI).
The patient presents with classic signs of hyperthyroidism and Graves-specific extrathyroidal manifestations (exophthalmos), which are driven by TSI antibodies stimulating the TSH receptor.
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Etiology / Epidemiology
Autoimmune TSH-receptor antibodies (TSI) stimulate the thyroid. Most common in women 20-40 years old.
Clinical Manifestations
Hyperthyroidism with diffuse goiter, exophthalmos, and pretibial myxedema.
Diagnosis
Low TSH, high Free T4, and positive TSH-receptor antibodies.
Treatment
Methimazole is first-line; agranulocytosis is the primary life-threatening side effect.
Prognosis
Risk of thyroid storm; monitor for atrial fibrillation and osteoporosis.
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Epidemiology & Etiology
Graves is an autoimmune disorder where TSH-receptor antibodies (TSI) mimic TSH, causing autonomous thyroid hormone production. It is the most common cause of hyperthyroidism in the US, predominantly affecting females.
Pertinent Anatomy
The thyroid gland undergoes diffuse hyperplasia and hypertrophy, leading to a palpable, non-tender, smooth goiter. Retro-orbital inflammation and fat deposition cause the characteristic exophthalmos.
Pathophysiology
TSI binds to the TSH receptor on thyroid follicular cells, bypassing the normal negative feedback loop. This results in excessive synthesis and release of T3 and T4. The systemic hypermetabolic state increases sensitivity to catecholamines.
Clinical Manifestations
Patients present with heat intolerance, palpitations, weight loss, and anxiety. Exophthalmos and lid lag are pathognomonic. Pretibial myxedema (thickened, indurated skin) is a specific cutaneous finding. Thyroid storm is a life-threatening emergency characterized by fever, delirium, and tachycardia.
Diagnosis
The TSH receptor antibody (TRAb) test is the most specific diagnostic marker. Labs show suppressed TSH (<0.01 mIU/L) and elevated Free T4. A radioactive iodine uptake (RAIU) scan shows diffuse, increased uptake throughout the gland.
Treatment
Methimazole is the preferred agent for most patients. Propylthiouracil (PTU) is reserved for the first trimester of pregnancy or thyroid storm due to hepatotoxicity. Agranulocytosis requires immediate cessation of therapy if fever or sore throat occurs. Radioactive iodine ablation is a definitive treatment but is contraindicated in pregnancy.
Prognosis
Long-term complications include atrial fibrillation and osteoporosis due to chronic thyrotoxicosis. Patients must be monitored for the development of permanent hypothyroidism following definitive treatment.
Differential Diagnosis
Toxic Multinodular Goiter: patchy uptake on RAIU scan
Thyroiditis: low RAIU uptake due to pre-formed hormone release
Exogenous Thyrotoxicosis: low RAIU uptake and low thyroglobulin
TSH-secreting Pituitary Adenoma: elevated TSH levels
Struma Ovarii: pelvic mass with thyroid tissue