Clinical Manifestations of Hyperthyroidism
Hyperthyroidism presents with a characteristic constellation of cardiovascular, neuropsychiatric, metabolic, and musculoskeletal symptoms that reflect the hypermetabolic state induced by excess thyroid hormone.
Cardiovascular Manifestations
The cardiovascular system bears the most clinically significant burden in hyperthyroidism, with symptoms that directly impact morbidity and mortality:
- Tachycardia and palpitations are nearly universal findings, driven by increased cardiac output (up to 300% above normal) and enhanced contractility 1, 2
- Hypertension occurs through a characteristic hemodynamic pattern: decreased systemic vascular resistance paradoxically triggers compensatory activation of the renin-angiotensin-aldosterone system, leading to sodium retention and blood volume expansion up to 25% 2
- Atrial fibrillation represents a critical complication with a 3-5 fold increased risk when TSH is below 0.1 mIU/L 3, 1
- Heart failure can develop in severe, long-standing cases despite typically increased contractility, particularly with persistent tachycardia or rapid atrial fibrillation 1, 2
- Pulmonary artery hypertension occurs because pulmonary blood flow increases without the same compensatory decrease in pulmonary vascular resistance seen systemically 1, 2
Cardiovascular complications are the chief cause of death after treatment of hyperthyroidism, especially in patients over 50 years 1, 2.
Neuropsychiatric and Neuromuscular Symptoms
The nervous system manifestations reflect thyroid hormone's effects on neural excitability and metabolism:
- Tremor of outstretched hands represents neuromuscular hyperexcitability and is a hallmark physical finding 4, 5
- Nervousness, anxiety, and irritability are common presenting complaints 1, 5, 6
- Insomnia and hyperactivity reflect the hypermetabolic state 1, 5
- Proximal muscle weakness is the hallmark musculoskeletal symptom, presenting as difficulty climbing stairs, rising from chairs, or lifting objects overhead 4
A critical pitfall: muscle weakness can present unilaterally, potentially diverting clinicians toward an unnecessary neurologic workup 7.
Metabolic and Dermatologic Features
These symptoms reflect the accelerated metabolic rate:
- Unintentional weight loss despite normal or increased appetite is characteristic 5, 8
- Heat intolerance and excessive sweating occur due to increased thermogenesis 1, 5, 6
- Diarrhea results from increased gastrointestinal motility 5
- Hair loss can occur with prolonged hyperthyroidism 1
Notably, weight gain can occasionally occur, representing an atypical presentation that should not exclude the diagnosis 7.
Thyroid-Specific Physical Findings
Examination findings vary by etiology:
- Diffusely enlarged thyroid gland (goiter) is typical in Graves' disease 5, 6
- Stare and exophthalmos are specific to Graves' disease and reflect thyroid eye disease 5
- Palpable thyroid nodules suggest toxic multinodular goiter or toxic adenoma 5
- Compressive symptoms (dysphagia, orthopnea, voice changes) occur with large toxic nodular goiters 5
Skeletal Manifestations
Bone health deteriorates with prolonged hyperthyroidism:
- Decreased bone mineral density occurs particularly in postmenopausal women with subclinical hyperthyroidism 3, 1
- Increased fracture risk (hip and spine) develops in women older than 65 years with TSH 0.1 mIU/L or lower 3
- Bone loss is reversible with treatment, though normalization of bone turnover may be delayed up to 1 year 3
Subclinical Hyperthyroidism Presentation
An important caveat: the only large population-based study (N=6,884) found no association between subclinical hyperthyroidism (TSH <0.21 mIU/L) and physical or psychological symptoms of hyperthyroidism 3. This contrasts with smaller hospital-based studies that did find more hyperthyroid-type symptoms. This suggests that mild subclinical disease may be asymptomatic in community populations, though cardiovascular and skeletal risks persist.
Life-Threatening Presentations
- Thyroid storm is a rare but life-threatening emergency characterized by severe thyrotoxicosis with fever, altered mental status, and cardiovascular collapse 1, 6
- Thyrotoxic periodic paralysis can occur, particularly in Asian males, presenting with acute flaccid paralysis 8