Hyperthyroidism
Overactive thyroid producing excess hormone. Suppresses TSH near zero; Graves' disease is the leading global cause.
What it is
Hyperthyroidism is the clinical state of excess thyroid hormone reaching tissues. The pituitary detects the high circulating T4 and suppresses TSH almost to zero — undetectable TSH is the hallmark lab finding. The most common cause worldwide is Graves' disease, an autoimmune condition where TSH-receptor antibodies stimulate the gland continuously. Other causes include toxic nodular goitre (autonomously functioning thyroid nodules), thyroiditis (a transient release of stored hormone), and exogenous (over-replacement with levothyroxine).
Key lab markers
- TSH — suppressed (typically <0.1 mIU/L in overt disease).
- Free T4 and free T3 — elevated. In T3 toxicosis only T3 is high.
- TSH receptor antibodies (TRAb) — distinguish Graves' from other causes.
- Thyroid uptake scan — distinguishes Graves' (high uniform uptake) from thyroiditis (low uptake) from toxic nodule (focal uptake).
Symptoms
- Heat intolerance, sweating
- Weight loss despite increased appetite
- Palpitations, tremor, anxiety
- Frequent bowel movements
- Insomnia
- Menstrual irregularity
- Muscle weakness
- Eye changes in Graves' (proptosis, lid lag)
- Goitre
When to discuss with a doctor
A suppressed TSH with elevated free T4 warrants prompt endocrinology evaluation. Atrial fibrillation, very rapid heart rate, severe muscle weakness or eye involvement are urgent presentations. Treatment options (antithyroid drugs, radioactive iodine, surgery) are nuanced and individualised — discuss thoroughly with a specialist before starting any therapy.