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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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