48. Hyperthyroidism - classification, etiology, pathogenesis, clinical manifestations.

Hyperthyroidism - classification, etiology, pathogenesis, and clinical manifestations.

Hyperthyroidism is a clinical syndrome caused by excess production and release of thyroid hormones (T3 and T4), leading to hypermetabolic state.

Classification

1. 1 According to cause

1. 2 According to morphology

Etiology

Primary hyperthyroidism

• Graves' disease (most common cause):
• Autoimmune; thyroid-stimulating immunoglobulins (TSI) stimulate TSH receptors.
• Toxic multinodular goiter (Plummer disease).
• Toxic adenoma (single hyperfunctioning nodule).
• Thyroiditis (transient hyperthyroid phase in subacute, silent, or postpartum thyroiditis).
• Excessive iodine intake (Jod- Basedow phenomenon).
• Excessive exogenous thyroid hormone intake (factitious hyperthyroidism).

Secondary hyperthyroidism

• TSH-secreting pituitary adenoma (rare).

Pathogenesis

1. Increased synthesis and secretion of thyroid hormones (T3 and T4) from thyroid gland (e.g., Graves', toxic nodules).
2. TSI stimulation (Graves' disease):

• Autoantibodies bind to TSH receptors → mimic TSH → continuous stimulation → diffuse gland hyperplasia.

1. 3 Resulting hormonal effects:

• Increased basal metabolic rate (BMR).
• Increased sympathetic activity due to upregulation of β- adrenergic receptors.
• Increased catabolism of proteins and lipids.

Clinical manifestations

General metabolic signs

• Weight loss despite increased appetite.
• Heat intolerance, excessive sweating.
• Hyperactivity, irritability, anxiety, insomnia.

Cardiovascular

• Palpitations, tachycardia, arrhythmias (e.g., atrial fibrillation).
• Increased cardiac output → potential heart failure in elderly.

Neuromuscular

• Tremor (fine, rapid).
• Proximal muscle weakness.
• Hyperreflexia.

Gastrointestinal

• Increased motility → diarrhea, frequent stools.

Skin and hair

• Warm, moist skin.
• Fine, thin hair.

Reproductive system

• Women: oligomenorrhea, amenorrhea.
• Men: gynecomastia, decreased libido.

Specific features in Graves' disease

• Diffuse goiter (symmetrically enlarged thyroid, may have bruit).
• Exophthalmos (proptosis): autoimmune inflammation of orbital tissues → eye protrusion.
• Pretibial myxedema: localized skin thickening over the shins.

Thyrotoxic crisis (thyroid storm)

• Acute, severe exacerbation of hyperthyroidism.
• Precipitated by stress, infection, surgery.
• High fever, severe tachycardia, delirium, dehydration → life- threatening.