Thyroid Function
Thyroid Function
 

Hypothyroidism

 
 
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Overview

  • Hypothyroidism refers to underactivity of the thyroid, with reduced circulating thyroid hormones. This is usually accompanied by typical signs and symptoms of hypothyroidism.
    • TFT Interpretation

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

Manifestations

    • Clinical Features

    • Symptoms

    • Weakness / lethargy / mental sluggishness
    • Weight gain
    • Cold intolerance
    • Dry, coarse skin
    • Constipation
    • Menorrhagia
    • Alopecia
    • Signs

    • Bradycardia
    • Psychomotor retardation
    • Impaired cognition
    • Cool, dry skin
    • Facial oedema
    • Loss of the outer ⅓ of the eyebrow
    • Tongue enlargement
    • Alopecia
    • Hyporeflexia
    • Non-pitting oedema

Primary Hypothyroidism

  • Hypothyroidism that originates from thyroid tissue.
    • Look For

    • Elevated TSH with reduced T4.
    • Causes of Primary Hypothyroidism

    • Autoimmune thyroiditis - Hashimoto’s, atrophic
    • Hypothyroid phase of thyroiditis
    • Iatrogenic - radioiodine therapy, thyroidectomy, external irradiation of the neck
    • Drugs - amiodarone, lithium, interferons, interleukin-2, iodide
    • Iodine deficiency
    • Thyroid infiltration - amyloidosis, tumour
    • Congenital hypothyroidism

Subclinical Hypothyroidism

  • Patients with subclinical hypothyroidism have TFT abnormalities without overt clinical features of hypothyroidism, or with nonspecific symptoms.
    • Look For

    • Elevated TSH with normal T4
    • No clinical features of hypothyroidism
    • Causes of Subclinical Hypothyroidism

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

    • Poor compliance with thyroxine
    • Assay interference
    • Drugs - amiodarone, sertaline
    • Nonthyroidal illness (recovery phase)
    • TSH receptor defects
    • TSH resistance
    • Pearls

    • Take a careful medication history
    • Ask about recent illnesses

Central Hypothyroidism

  • Pituitary or hypothalamic lesions are a less common cause of hypothyroidism.
    • Look For

    • Reduced / normal TSH with reduced T4.
    • Causes of Central Hypothyroidism

      Pituitary or hypothalamic pathology.
    • Tumour
    • Trauma
    • Surgery
    • Radiation
    • Infection
    • Infarction
    • Infiltration
    • Differential Diagnosis of TFT Findings

    • Nonthyroidal illness
    • Recent treatment of hyperthyroidism
    • Congenital TSH or TRH deficiency
    • Assay interference
 
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