Hypothyroidism
April 28th, 2020
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 1/3 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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