Pathophysiology
HLA-DR3/DR5-linked autoimmunity: cytotoxic T cells and anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin antibodies destroy follicular cells. Histology shows Hurthle cells and germinal centres.
Sources: ATA Guidelines for Hypothyroidism (Thyroid 2014;24:1670); ETA 2023 Guideline on the Management of Subclinical Hypothyroidism
Clinical presentation
Fatigue, cold intolerance, weight gain, constipation, dry skin, bradycardia, delayed reflex relaxation, menorrhagia, non-pitting oedema (myxoedema). Painless firm goitre initially, atrophic gland late.
Sources: ATA Guidelines for Hypothyroidism (Thyroid 2014;24:1670); ETA 2023 Guideline on the Management of Subclinical Hypothyroidism
Diagnosis
Elevated TSH with low free T4 confirms overt hypothyroidism. Subclinical: raised TSH with normal free T4. Positive anti-TPO antibodies (>90% of cases) establish autoimmune aetiology; ultrasound shows heterogeneous, hypoechoic gland.
Sources: ATA Guidelines for Hypothyroidism (Thyroid 2014;24:1670); ETA 2023 Guideline on the Management of Subclinical Hypothyroidism
Management
Levothyroxine 1.6 mcg/kg/day, start lower (25-50 mcg) in elderly or coronary disease. Take fasting, 30-60 min before breakfast, away from calcium/iron/PPI. Recheck TSH at 6-8 weeks; target TSH 0.5-2.5 mIU/L in most adults.
Sources: ATA Guidelines for Hypothyroidism (Thyroid 2014;24:1670); ETA 2023 Guideline on the Management of Subclinical Hypothyroidism
Associations
Increased risk of other autoimmune disease (type 1 diabetes, Addison, coeliac, vitiligo) and primary thyroid lymphoma. Postpartum thyroiditis is a variant.
Sources: ATA Guidelines for Hypothyroidism (Thyroid 2014;24:1670); ETA 2023 Guideline on the Management of Subclinical Hypothyroidism
