PA31.1-3 | Thyroid: Goiter, Thyroiditis & Thyroid Function Disorders — Summary & Reflection

REFLECT

Return to the opening clinical scenario:

Mother (rural Jharkhand, euthyroid goiter → 10 years later, palpitations, weight loss, exophthalmos, undetectable TSH):
• Initial presentation: diffuse nontoxic goiter from iodine deficiency → compensatory TSH rise → thyroid hyperplasia. Euthyroid at that stage.
• Ten years later: evolution to autonomous nodule(s) or concurrent development of Graves disease. The undetectable TSH and bilateral proptosis strongly favour Graves disease (TRAb-driven). Note: long-standing MNG can rarely develop autonomous function (toxic MNG/Plummer), but proptosis is specific to Graves.

Daughter (poor concentration, short stature, cold intolerance since age 8):
• Strongly suggestive of endemic cretinism or congenital/early-childhood hypothyroidism from iodine deficiency
• TSH would be markedly elevated, free T4 low, RAIU low-normal (substrate-deficient synthesis)
• The intellectual disability caused by iodine deficiency in the first 3 years of life is irreversible — highlighting why universal iodisation of salt is a critical public health intervention

Broader reflection: How does the same iodine deficiency lead to such different clinical endpoints in these two individuals? Consider the age of onset, the degree of deficiency, and the interplay of genetic susceptibility to autoimmunity.

KEY TAKEAWAYS

Thyroid Pathology — Key Takeaways

1. Goiter (PA31.1)
• Diffuse nontoxic goiter: iodine deficiency → ↑TSH → hyperplasia; colloid phase has scalloped distended follicles
• MNG: repeated hyperplasia-involution cycles → heterogeneous nodules with hemorrhage, fibrosis, calcification
• Iodine dependency: endemic in Himalayan belt; corrected by salt iodisation

2. Thyroiditis (PA31.1)
• Hashimoto: autoimmune (anti-TPO, cytotoxic T-cells) → lymphocytes + germinal centres + Hürthle cells → hypothyroidism; risk of MALToma
• de Quervain: post-viral, granulomas with giant cells, painful, 4-phase course, RAIU suppressed in toxic phase
• Subacute lymphocytic/postpartum: painless, RAIU suppressed, self-limiting, lymphocytes without Hürthle cells
• Riedel: IgG4-related, rock-hard fibrosis, paucicellular

3. Graves Disease (PA31.2)
• TSI antibodies → persistent TSHR activation → unregulated T3/T4 synthesis
• Morphology: tall cells, papillary infoldings, scalloped colloid
• Extrathyroidal: proptosis (orbital GAG), pretibial myxoedema, acropachy
• RAIU: high and diffuse

4. Thyrotoxicosis vs. Hypothyroidism (PA31.3)
• Hyper: tachycardia, weight loss, heat intolerance, diarrhoea, hyperreflexia, ↓TSH, ↑fT4, ↑RAIU (Graves) or ↓RAIU (thyroiditis)
• Hypo: bradycardia, weight gain, cold intolerance, constipation, delayed DTR relaxation, myxoedema, ↑TSH, ↓fT4
• Most common causes: Graves (hyper), Hashimoto/iodine deficiency (hypo)
• RAIU is the master key to distinguish productive from destructive/exogenous thyrotoxicosis