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KEY FEATURES

ESSENTIALS OF DIAGNOSIS

  • Hyperreflexia, tremor

  • Low (suppressed) thyroid-stimulating hormone (TSH) levels (below the lower limit of normal)

  • High free T4, total T4, and free thyroxine index, and/or high free T3 or total T3 radioimmunoassay

  • High 24-hour radioactive iodine uptake in Graves’ disease or toxic multinodular goiter; low uptake in thyroiditis or exogenous cause.

  • Goiter (often with a bruit) and exophthalmos in Graves’ disease

GENERAL CONSIDERATIONS

  • Hyperthyroidism increases levels of T3, which enhances myocardial systolic and diastolic function

  • Beta catecholamine receptor responsiveness is increased, also leading to effects mimicking sympathetic nervous system activation such as increased heart rate

  • Although cardiac performance is augmented, the heart functions at near capacity in hyperthyroidism, with little reserve

  • Hyperthyroidism can be caused by:

    • – Diseases of the thyroid gland such as Graves’ disease

    • – Exogenous agents such as amiodarone

    • Rare thyroid hormone–producing tumors such as struma ovarii

  • In apathetic hyperthyroidism of the elderly, atrial fibrillation may be the only manifestation

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

  • Weight loss despite increased appetite

  • Nervousness, anxiety, insomnia

  • Heat intolerance, diaphoresis, diarrhea

  • Proximal muscle weakness

  • Palpitations, dyspnea, chest pain

PHYSICAL EXAM FINDINGS

  • Stare, lid retraction and lag

  • Exophthalmos in Graves’ disease

  • Goiter

  • Tachycardia, loud heart sounds, flow murmurs

  • Hyperreflexia

  • Pretibial myxedema

DIFFERENTIAL DIAGNOSIS

  • Anxiety disorder

  • Factitious or iatrogenic thyrotoxicosis

  • Angina, atrial fibrillation, and other signs without thyrotoxicosis

DIAGNOSTIC EVALUATION

LABORATORY TESTS

  • Reduced TSH, elevated free T4 and T3

ELECTROCARDIOGRAPHY

  • Sinus tachycardia in many

  • Atrial fibrillation in some

IMAGING STUDIES

  • Echocardiography:

    • – Hypercontractile state

    • – Left ventricular hypertrophy

    • – Left atrial enlargement in some patients

DIAGNOSTIC PROCEDURES

  • Radioactive iodine thyroid uptake may be increased or decreased, depending on the cause of hyperthyroidism

TREATMENT

CARDIOLOGY REFERRAL

  • Atrial fibrillation

  • Heart failure

  • Acute coronary syndromes

HOSPITALIZATION CRITERIA

  • Atrial fibrillation

  • Heart failure

  • Acute coronary syndromes

MEDICATIONS

  • Beta blockers to reduce heart rate and improve symptoms

    • – Propranolol is preferred because it blocks peripheral conversion of T4 to T3

  • Thionamides to block thyroid hormone release and prevent synthesis

THERAPEUTIC PROCEDURES

  • Radioactive iodine ablation

SURGERY

  • Subtotal thyroidectomy in selected cases

MONITORING

  • ECG monitoring in hospital as appropriate

  • TSH monitoring during treatment

DIET AND ACTIVITY

  • Restricted activity until thyroid controlled

ONGOING MANAGEMENT

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