Paper II
Question
Write a short note on Hashimoto thyroiditis
Answer
Hashimoto thyroiditis is the most common cause of hypothyroidism in iodine-sufficient areas, an autoimmune disorder characterized by progressive destruction of thyroid parenchyma.
Pathogenesis
- Autoimmune destruction mediated by both humoral (antibodies against thyroglobulin and thyroid peroxidase) and cell-mediated (cytotoxic T-cell) mechanisms
- Sensitized CD8+ cytotoxic T cells directly kill thyroid follicular cells; CD4+ T cells release cytokines that activate macrophages and further damage follicular cells
Clinical features
- More common in women (female:male ratio ~10-20:1), typically middle-aged
- Painless, diffuse, often symmetric goitre
- Gradual onset of hypothyroidism (fatigue, cold intolerance, weight gain, constipation); may have a transient hyperthyroid phase (Hashitoxicosis) early in the disease from follicular disruption releasing stored hormone
Morphology
- Diffusely enlarged thyroid, pale tan-grey, well-encapsulated, firm
- Microscopically: dense lymphoplasmacytic infiltrate with well-formed lymphoid germinal centres, atrophic thyroid follicles, and characteristic Hürthle cell (oncocytic) change in follicular epithelium (enlarged cells with abundant eosinophilic granular cytoplasm)
Laboratory findings
- Elevated anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin antibodies
- Elevated TSH, low free T4 (in established hypothyroidism)
Associations
- Increased risk of other autoimmune diseases and of thyroid lymphoma (rare but notable long-term complication)