Graves' Disease
Overview
Graves' Disease is the most common cause of hyperthyroidism, accounting for 70-80% of cases. It is an autoimmune disorder caused by Thyroid-Stimulating Immunoglobulins (TSI), which bind and activate the TSH receptor, causing continuous, unregulated thyroid stimulation.
Clinical Triad
- Diffuse Toxic Goitre: Symmetrical, smooth, vascular thyroid enlargement. Bruit audible on auscultation.
- Pretibial Myxedema (Dermopathy): Non-pitting, indurated orange-peel skin over the anterior shins. Caused by TSI stimulating skin fibroblasts.
- Thyroid Eye Disease (Ophthalmopathy): Bilateral proptosis, lid lag, lid retraction. Caused by TSI causing glycosaminoglycan deposition in extraocular muscle bellies and orbital fat.
Imaging Features
- Thyroid Ultrasound: Diffusely enlarged, heterogeneous, hypoechoic gland. Markedly increased vascularity on Doppler ('thyroid inferno').
- Nuclear Medicine (Tc-99m Pertechnetate/I-123): Dramatically high diffuse uptake by stimulated follicular cells — distinguishes Graves' from destructive thyroiditis (low uptake) or toxic nodule (hot focus with suppressed background).
- MRI Orbit: Enlarged extraocular muscle bellies (superior and inferior recti most affected) with sparing of the tendons in thyroid eye disease.
WarningThyroid Storm: A Medical Emergency
Thyroid storm is a life-threatening exacerbation of hyperthyroidism (fever, tachycardia, altered consciousness, heart failure). Precipitants: infection, surgery, radioiodine. Management: Propylthiouracil (blocks synthesis AND T4-to-T3 conversion), Lugol's iodine (blocks hormone release), propranolol (blocks peripheral effects), and corticosteroids.
High Yield Facts
LightbulbFRCR / MD Prep Pearl
Distinguishing Graves' from Hashimoto's thyroiditis: both can present with goitre. Graves' = hyperthyroid with high radioiodine uptake. Hashimoto's = hypothyroid with LOW uptake (or initially transient hyperthyroid in 'Hashitoxicosis'). Both have elevated thyroid antibodies but different types (TSI in Graves; TPO/TG antibodies in Hashimoto's).