Overview.
Hyperthyroidism occurs when your thyroid gland produces too much thyroid hormone, speeding up your metabolism and affecting your heart, bones, and nervous system. While less common than hypothyroidism, it requires prompt recognition because it can cause serious complications including heart arrhythmias, bone loss, and thyroid storm—a medical emergency.
In hyperthyroidism, excess thyroid hormone accelerates metabolic processes throughout the body. Your heart beats faster, you lose weight despite eating more, you feel anxious and overheated. The most common cause is Graves' disease, an autoimmune condition. Other causes include toxic nodules, thyroiditis, and excess thyroid medication.
Prevalence: Hyperthyroidism affects about 1-2% of the population, with women 5-10 times more likely to develop it than men. Graves' disease typically affects women in their 30s-50s. The condition is slightly more common in areas with iodine deficiency.
Medical name: Thyrotoxicosis
Symptoms.
Early warnings
- Unexplained weight loss despite good appetite
- Rapid or irregular heartbeat
- Increased sweating and heat intolerance
- Nervousness, anxiety, or irritability
- Tremor in hands and fingers
- Changes in menstrual patterns
- Increased bowel movements
- Muscle weakness
Classic symptoms
- Weight loss despite increased appetite
- Rapid, pounding, or irregular heartbeat
- Nervousness, anxiety, irritability
- Tremor of hands and fingers
- Heat intolerance and increased sweating
- Frequent bowel movements
- Enlarged thyroid (goiter)
- Fatigue and muscle weakness
- Difficulty sleeping
- Thinning skin and fine hair
- Eye changes (Graves' disease): bulging, redness, double vision
Progression
Untreated hyperthyroidism can lead to atrial fibrillation, heart failure, osteoporosis, and thyroid storm (a life-threatening emergency with fever, rapid heart rate, and confusion). Even mild cases increase fracture risk and cardiovascular events over time.
Risk factors.
- Female sex
- Family history of thyroid disease
- Other autoimmune conditions
- Recent pregnancy (postpartum thyroiditis)
- Excessive iodine intake (supplements, contrast dye, medications)
- Smoking (specifically increases Graves' eye disease risk)
- High stress or trauma
- Age 20-40 for Graves' disease
Lab interpretation.
Key biomarkers
- TSH — Suppressed (<0.1-0.4 mIU/L); often undetectable (<0.01) (primary)
- Free T4 — Elevated above reference range in overt hyperthyroidism (primary)
- Free T3 — Often elevated even more than T4; T3 toxicosis can occur alone (primary)
- TSH Receptor Antibodies (TRAb) — Positive in Graves' disease (secondary)
Diagnostic criteria
- Overt hyperthyroidism: TSH <0.1 mIU/L with elevated Free T4 and/or Free T3
- Subclinical hyperthyroidism: TSH <0.4 mIU/L with normal Free T4 and Free T3
- T3 toxicosis: Low TSH, normal Free T4, elevated Free T3
- Graves' disease confirmed by positive TRAb antibodies
- Thyroid uptake scan can distinguish causes
Recommended panels
When & next steps.
When to test
- Unexplained weight loss
- Rapid or irregular heartbeat, palpitations
- Anxiety, tremor, nervousness
- Heat intolerance and excessive sweating
- New-onset atrial fibrillation
- Eye symptoms (bulging, redness, double vision)
- Goiter or thyroid nodule
- Family history of Graves' disease
If suspected
- Order TSH, Free T4, and Free T3
- If TSH suppressed, add TRAb (TSH receptor antibodies)
- Consider thyroid uptake and scan to identify cause
- Check EKG if palpitations present
- Urgent referral if severe symptoms (fever, confusion, very rapid heart rate)
If confirmed
- Referral to endocrinologist for treatment planning
- Beta-blockers for symptom relief (heart rate, tremor)
- Treatment options: antithyroid drugs, radioactive iodine, or surgery
- Graves' eye disease needs ophthalmology evaluation
- Monitor TSH and Free T4 frequently during treatment
- Most patients become hypothyroid after definitive treatment
FAQs.
Can hyperthyroidism go away on its own?
Some forms can: subacute thyroiditis and postpartum thyroiditis often resolve within months. Graves' disease rarely remits permanently without treatment, though antithyroid drugs may induce remission in 30-50% of patients.
Is radioactive iodine safe?
Yes, radioactive iodine (RAI) has been used safely for decades. It's taken as a single oral dose and specifically targets thyroid tissue. Most patients eventually need thyroid hormone replacement after RAI.
Why might I have symptoms with 'normal' labs?
TSH changes before Free T4/T3 normalize. Also, symptoms can persist briefly after labs normalize. Some people are more sensitive to small thyroid hormone changes. Finally, there may be coexisting conditions.
What is thyroid storm?
Thyroid storm is a life-threatening emergency with very high thyroid hormone levels causing fever, rapid heart rate, confusion, and organ failure. It requires immediate hospitalization and aggressive treatment. It's rare but can be triggered by infection, surgery, or stopping medication.