Hyperthyroidism

Hyperthyroidism is an endocrine disorder characterised by the excessive production of thyroid hormones by the thyroid gland. These hormones, chiefly thyroxine and triiodothyronine, regulate metabolic processes in nearly all body tissues; their overproduction therefore produces widespread systemic effects. The broader condition of thyrotoxicosis refers to elevated circulating thyroid hormone levels from any cause, and thus includes but is not limited to hyperthyroidism.

Clinical Presentation

The clinical features of hyperthyroidism vary according to age, comorbid disease and the underlying cause. While some individuals remain asymptomatic, others develop a constellation of metabolic, cardiovascular, neurological and psychological symptoms.
Common manifestations include irritability, heightened nervousness, increased perspiration, tachycardia, palpitations, heat intolerance, hand tremors, muscular weakness and insomnia. Gastrointestinal hypermotility may lead to frequent bowel movements or diarrhoea. Despite increased appetite, many people experience weight loss; however, a minority may gain weight. Women may notice lighter menstrual flow or prolonged cycles.
Thyroid hormones amplify the effect of the sympathetic nervous system, producing symptoms akin to those seen with excessive catecholamine activity. These may include tremors, anxiety, hyperactivity, emotional lability and reduced serum cholesterol concentrations. In more severe cases, arrhythmias such as atrial fibrillation develop, particularly in older adults. Prolonged untreated disease can contribute to osteoporosis due to accelerated bone turnover and decreased bone density, with postmenopausal women being especially susceptible.
Neurological findings may comprise myopathy, choreiform movements and, in some individuals of Asian descent, thyrotoxic periodic paralysis. An established association exists between autoimmune thyroid disease and myasthenia gravis, with a small proportion of affected individuals showing coexistent hyperthyroidism.
Ocular manifestations vary by cause. In Graves’ disease, immune-mediated inflammation of tissues behind the eyes leads to characteristic exophthalmos. Minor ocular signs, such as eyelid retraction, lid lag and extraocular muscle weakness, may appear in any form of hyperthyroidism but typically resolve with treatment.

Thyroid Storm

Thyroid storm is a critical and life-threatening exacerbation of thyrotoxicosis, presenting with sudden and severe hyperthermia, arrhythmias, vomiting, diarrhoea and acute mental status changes. It usually arises from untreated or undertreated hyperthyroidism and is often triggered by infections or other physiological stresses. Immediate hospital management is essential, as mortality remains high and is frequently due to multiorgan failure.

Causes

A range of pathological processes can give rise to hyperthyroidism. The most common cause in many regions, including the United States, is Graves’ disease, an autoimmune disorder in which thyroid-stimulating immunoglobulins activate the thyroid gland. Other frequent causes include:

• multinodular goitre with autonomous hormone production;
• toxic adenoma, where a single nodule hypersecretes hormone;
• thyroiditis, in which inflammation leads to the release of preformed hormones;
• excessive iodine intake;
• excessive consumption of synthetic thyroid hormones.

Less commonly, a pituitary adenoma producing thyroid-stimulating hormone may drive thyroid hormone overproduction.

Diagnosis

Diagnosis is guided by clinical assessment and confirmed through laboratory evaluation. Suppressed thyroid-stimulating hormone (TSH) with elevated thyroxine or triiodothyronine strongly suggests hyperthyroidism. Additional tests may include:

• radioactive iodine uptake and thyroid scans to identify overactive tissue;
• measurement of antithyroid antibodies, particularly thyrotropin receptor antibodies, which support a diagnosis of Graves’ disease.

These investigations help differentiate between causes and guide management decisions.

Treatment Approaches

Management strategies depend on the underlying aetiology, symptom severity and patient-specific factors. The principal treatment options include:
Radioiodine TherapyRadioactive iodine-131 is administered orally, concentrating in the thyroid gland and gradually destroying overactive tissue. Hypothyroidism frequently follows and is managed with lifelong synthetic thyroid hormone replacement.
MedicationSymptomatic control is often achieved with beta blockers to reduce tremors, palpitations and anxiety. Antithyroid drugs such as methimazole inhibit hormone synthesis and may be used as definitive therapy or as a preparatory measure before radioiodine treatment or surgery.
SurgeryThyroidectomy is considered in individuals with large goitres, when malignancy is a concern or when other treatments are unsuitable. Postoperative hypothyroidism is common and treated with hormone replacement.

Epidemiology

Hyperthyroidism affects approximately 1–2 per cent of the population in the United States and about 2–5 per cent of adults worldwide. It occurs significantly more often in women than in men and commonly presents between the ages of 20 and 50. Prevalence increases with age, and the condition is more common in those over 60 years.
Hyperthyroidism represents a significant endocrine disorder with diverse systemic implications. Early recognition and appropriate treatment usually result in excellent outcomes, while delays in management may lead to severe complications, including thyroid storm, cardiovascular disease and bone fragility.