Makindo Medical Notes

Related Subjects: |Thyrotoxicosis and Hyperthyroidism |Thyroid Storm - Thyrotoxic crisis |Graves' Disease (Thyrotoxicosis) |Amiodarone and Thyroid disease |Thyroid Surgery (Thyroidectomy) |Hypothyroidism |Hashimoto's thyroiditis |DeQuervain's thyroiditis |Subacute Thyroiditis |Thyroid nodule |Congenital Hypothyroidism |Thyroid Function Tests and antibodies |Post partum thyroiditis |Sick Euthyroid Syndrome |Thyroid Exam (OSCE) |Thyroid Gland anatomy and Physiology |Thyroid Cancer

🦋 Hashimoto thyroiditis is the most common cause of hypothyroidism in iodine-sufficient countries. It is an autoimmune lymphocytic thyroiditis characterised by high titres of thyroid peroxidase (TPO) antibodies and a gradual loss of thyroid function. 🔑 Think of it as "autoimmune attack → gland destruction → hypothyroidism."

📖 About

• Chronic autoimmune inflammation of the thyroid gland, also called chronic lymphocytic thyroiditis.
• Often presents with a firm, rubbery, and sometimes nodular thyroid (goitre).
• Most common in middle-aged women (F:M ratio ~10:1).
• Associated with HLA-DR3 and HLA-DR5.

🧬 Aetiology & Pathogenesis

• Mediated by autoantibodies (anti-TPO, anti-thyroglobulin) and T-cell infiltration.
• Follicular destruction → loss of thyroid hormone production.
• High titres of TPO antibodies present in 90–100% of cases.
• Hashitoxicosis: early transient hyperthyroid phase caused by follicular breakdown releasing stored hormone.

🤝 Associations with Other Autoimmune Conditions

• Pernicious anaemia (B12 deficiency).
• Addison’s disease, vitiligo, type 1 diabetes mellitus.
• Rheumatoid arthritis, systemic lupus erythematosus (SLE), coeliac disease.
• Premature greying of hair, hypoparathyroidism.

🩺 Clinical Features

• Symptoms of hypothyroidism: tiredness, lethargy, weight gain, depression, cold intolerance.
• Dry skin, coarse hair, hoarse voice, slow-relaxing reflexes (“hung-up” reflex).
• Menstrual disturbances (menorrhagia or oligomenorrhoea).
• Bradycardia, pericardial effusion, heart failure in severe cases (myxoedema).
• Goitre may be diffusely enlarged or atrophic in late disease.
• Hashitoxicosis: transient hyperthyroid symptoms (palpitations, tremor, anxiety) in early phase.

🔬 Investigations

• Thyroid function tests: Raised TSH with low free T4 (primary hypothyroidism).
• Autoantibodies: High anti-TPO and anti-thyroglobulin antibodies.
• Anaemia (macrocytic if pernicious anaemia; normocytic otherwise).
• Biochemistry: Hyponatraemia, raised cholesterol, raised CK (myopathy).
• Ultrasound: hypoechoic, heterogeneous gland with pseudonodules.

🔀 Differential Diagnosis

• Primary hypothyroidism (non-autoimmune).
• Postpartum thyroiditis (transient, self-limiting, within 1 year of delivery).
• Iodine deficiency goitre.
• Pendred syndrome (goitre + congenital deafness).
• Subacute (De Quervain’s) thyroiditis: painful, post-viral, raised ESR.

💊 Management

• Levothyroxine replacement (usually 50–100 mcg/day; lifelong).
• Start low (25 mcg/day) in elderly or those with ischaemic heart disease; titrate slowly.
• Aim for TSH normalisation, check TFTs 6–8 weeks after dose adjustment.
• Monitor annually once stable.
• Screen for other autoimmune conditions if clinical suspicion.

📈 Prognosis

• Usually good with treatment; symptoms improve once euthyroidism restored.
• Children: untreated hypothyroidism can → growth retardation & intellectual impairment (cretinism).
• Elderly: symptoms may be subtle → delayed recognition.
• Increased risk of thyroid lymphoma (rare but important to remember).