Thyroid Function
 

Hyperthyroidism

 
 
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Overview

  • Hyperthyroidism refers to hyperactivity of the thyroid gland, with increased circulating thyroid hormones. This tends to be accompanied by typical signs and symptoms of thyrotoxicosis such as those listed below.
    • TFT Interpretation

    • Primary hyperthyroidism -  reduced TSH with elevated T4
    • Subclinical hyperthyroidism - reduced TSH with normal T4
    • Central hyperthyroidism - elevated TSH with elevated T4

Manifestations

    • Clinical Features

    • Symptoms

    • Weight loss despite increased appetite
    • Hyperactivity / irritability
    • Heat intolerance
    • Tremor
    • Sweating
    • Palpitations
    • Diarrhoea
    • Amenorrhoea
    • Alopecia
    • Signs

    • Sinus tachycardia / atrial fibrillation
    • Psychomotor agitation
    • Fine tremor
    • Warm skin
    • Onycholysis
    • Palmar erythema
    • Muscle wasting / weakness
    • Hyperreflexia
    • Alopecia
    • Gynaecomastia
    • Manifestations of Grave’s

    • Exophthalmos
    • Proptosis
    • Periorbital / lid swelling and chemosis
    • Lid lag
    • Diplopia, poor convergence, limited upward gaze
    • Corneal ulcers (exposure keratitis)
    • Decreased visual acuity (retinal and optic nerve oedema)
    • Pretibial myxoedema

Primary Hyperthyroidism

  • Hyperthyroidism that originates from thyroid tissue.
    • Look For

    • Suppressed TSH with elevated T3 and elevated or normal T4.
    • Causes of Primary Hyperthyroidism

    • Grave’s disease
    • Toxic multinodular goitre
    • Toxic nodule
    • Thyroiditis - postviral, postpartum, lymphocytic
    • Thyroxine - excess replacement, thyrotoxicosis factitia
    • Drugs - amiodarone, iodine
    • Pregnancy-related - hyperemesis gravidarum, hydatidiform mole
    • Struma ovarii
    • Congenital hyperthyroidism

Subclinical Hyperthyroidism

  • Patients with subclinical hyperthyroidism have TSH suppression and normal T4 without overt clinical features of hyperthyroidism, or with nonspecific symptoms.
    • Look For

    • Reduced TSH with normal T4
    • No clinical features of hyperthyroidism
    • Causes of Subclinical Hyperthyroidism

    • As per primary hyperthyroidism.
    • Differential Diagnosis of TFT Findings

    • Recent treatment of hyperthyroidism
    • Intermittent thyroxine
    • T3 thyrotoxicosis
    • Nonthyroidal illness
    • Drugs - steroids, dopamine, dobutamine
    • Pearls

    • If the patient is clinically thyrotoxic, consider T3 toxicosis and check the patient’s T3.
    • Take a careful medication history, including past treatment for hyper or hypothyroidism.
    • Ask about recent illnesses.

Central Hyperthyroidism

  • TSH-secreting pituitary tumours are rare.
    • Look For

    • Normal / elevated TSH with elevated T4.
    • Differential Diagnosis of TFT Findings

    • Thyroid hormone resistance
    • Acute psychiatric illness
    • Drugs - amiodarone, heparin
    • Familial dysalbuminaemic hyperthyroxinaemia
    • Assay interference
 
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