Hashimoto's Thyroiditis
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Hashimoto's Thyroiditis (Chronic Lymphocytic Thyroiditis) is the most common cause of hypothyroidism in iodine-sufficient regions. It is an organ-specific autoimmune disease where the immune system attacks thyroid follicular cells, leading to progressive fibrosis and failure.
Key Clinical Features
- Hypothyroidism: Fatigue, weight gain, cold intolerance.
- Goitre: Often firm, rubbery, and non-tender initially, later becoming atrophic.
- Antibodies: Hallmark is the presence of Anti-Thyroid Peroxidase (Anti-TPO) antibodies.
Clinical Scenario: The Tired Teacher
A 34-year-old female teacher presents with 6 months of increasing fatigue, 'brain fog', dry skin, and constipation. She has gained 5kg despite poor appetite. Her mother has 'thyroid problems'. Examination reveals a firm, non-tender goitre and delayed relaxation of ankle jerks.
Key Teaching Points
- Classic presentation of overt hypothyroidism.
- Family history is a strong risk factor for autoimmune thyroid disease.
- Delayed relaxation of deep tendon reflexes (Woltman's sign) is a specific sign.
- First-line investigation is TSH and Free T4. If TSH is high, check Anti-TPO antibodies to confirm Hashimoto's.
- Prevalence: Affects 1-2% of the population; Anti-TPO antibodies are found in up to 10% of women.
- Sex: Strong female predominance (7:1 to 15:1 ratio).
- Age: Peak incidence 30–50 years, but prevalence increases with age.
- Genetics: Polygenic. Associated with HLA-DR3, HLA-DR5, and CTLA-4 polymorphisms. High concordance in twins.
The destruction of the thyroid is mediated by both cellular and humoral immunity.
- Loss of Tolerance: Breakdown in self-tolerance to thyroid antigens (Thyroid Peroxidase, Thyroglobulin).
- Infiltration: Lymphocytes (T and B cells) infiltrate the thyroid gland.
- Destruction:
- CD8+ Cytotoxic T-cells cause direct follicular cell death.
- Autoantibodies (Anti-TPO, Anti-Tg) fix complement and induce cytotoxicity (ADCC).
- Histology:
- Diffuse lymphocytic infiltration with germinal centres.
- Hürthle cells (Ashkenazy cells): Eosinophilic, metaplastic follicular cells.
- Fibrosis eventually replaces thyroid tissue.
Associated Autoimmune Conditions (Polyautoimmunity)
Hashimoto's patients are at higher risk for:
- Vitiligo.
- Type 1 Diabetes Mellitus.
- Addison's Disease (Schmidt's Syndrome).
- Pernicious Anaemia (B12 deficiency).
- Coeliac Disease.
- Rheumatoid Arthritis / SLE.
Onset is insidious. Patients may be asymptomatic (Subclinical Hypothyroidism) or present with overt failure.
Metabolic (Slowing Down)
Neurological / Psychiatric
Dermatological
Gastrointestinal
Cardiovascular
Reproductive
Local
Hashitoxicosis
- General: Appropriate clothing for weather? Slow movement/speech? Puffy face?
- Hands: Dry skin, cool peripheries, bradycardia.
- Nails: Brittle, onycholysis.
- Neck:
- Inspect: Goitre? Scars?
- Palpate: Stand behind. Hashimoto's gland feels firm and "rubbery" or "pebbly". Check for lymphadenopathy (lymphoma risk).
- Percuss: Retrosternal dullness?
- Auscultate: Bruits (rare in Hashimoto's, common in Graves').
- Neurological: Test ankle reflexes (delayed relaxation). Check for proximal myopathy.
Biochemistry
- TSH: High (>10 mU/L in overt disease). The most sensitive screening test.
- Free T4: Low in overt disease; Normal in subclinical disease.
- Autoantibodies:
- Anti-TPO: Positive in >90%.
- Anti-Thyroglobulin (Anti-Tg): Positive in ~60% (less sensitive).
- Lipids: Hypercholesterolaemia (often resolves with treatment).
- CK: Often elevated.
- Sodium: Hyponatraemia (SIADH-like picture).
- FBC: Macrocytic anaemia (B12 deficiency/pernicious anaemia overlap) or normocytic anaemia.
Imaging
- Ultrasound: Typically shows a heterogeneous, hypoechoic gland ("moth-eaten" appearance) with pseudonodules. Useful if a dominant nodule is palpable to exclude malignancy.
Procedures
- FNAC (Fine Needle Aspiration Cytology): Rarely indicated unless a discrete nodule is suspicious (rapid growth, dominant nodule).
Goal: Restore euthyroidism (normal TSH) and alleviate symptoms.
Medical Therapy: Levothyroxine (T4)
- Standard Dose: 1.6 mcg/kg/day (approx. 100–125 mcg daily for adults).
- Administration: Take on an empty stomach (30-60 mins before breakfast) with water. Calcium, iron, and PPIs interfere with absorption (separate by 4 hours).
- Initiation:
- Young/Healthy: Start full dose.
- Elderly / Ischaemic Heart Disease: Start low (25–50 mcg) and titrate up slowly ("start low, go slow") to avoid precipitating angina/arrhythmia.
Monitoring
- Check TSH every 6–8 weeks after dose change.
- Once stable, check annually.
- Target: TSH 0.5 – 2.5 mU/L (or within local reference range, typically 0.4-4.0).
Subclinical Hypothyroidism (TSH High, T4 Normal)
- Treat if:
- TSH > 10.
- Symptoms compatible with hypothyroidism.
- Positive Anti-TPO antibodies.
- Pregnancy or trying to conceive.
- Goitre.
- Monitor if: TSH 4–10, asymptomatic, no antibodies. (Repeat annually).
Special Situation: Pregnancy
- Crucial: Fetus relies on maternal T4 in first trimester (brain development).
- Action: Increase Levothyroxine dose by 25–50% (or add 2 extra tablets/week) as soon as pregnancy is confirmed.
- Refer to endocrinology/obstetric medicine. Anti-TPO positive women need close monitoring even if euthyroid.
Myxoedema Coma (Emergency)
- Severe, decompensated hypothyroidism.
- Triggers: Infection, cold exposure, stopping meds.
- Features: Hypothermia, altered mental status, bradycardia, hypoventilation.
- Rx: IV Levothyroxine + IV Liothyronine (T3) + Hydrocortisone (to cover adrenal insufficiency) + Passive warming.
Disease-Related
- Myxoedema Coma: High mortality (20-40%).
- Thyroid Lymphoma: Increased risk of Primary Thyroid Lymphoma (Non-Hodgkin B-cell). Suspect if rapid goitre growth.
- Cardiovascular Disease: Dyslipidaemia and hypertension increase atherosclerosis risk.
- Infertility: Anovulation.
Treatment-Related
- Over-replacement (Iatrogenic Thyrotoxicosis): Risk of Atrial Fibrillation and Osteoporosis (post-menopausal women).
- Lifelong Condition: Permanent destruction of the gland means lifelong replacement is usually needed.
- Quality of Life: Most patients return to full health. Some report persistent symptoms despite biochemical euthyroidism (controversial area; T3/T4 combination therapy is not routinely recommended by NICE but discussed in specialist settings).
- Goitre: Usually shrinks with T4 treatment (TSH suppression reduces stimulation).
- NICE Guideline [NG145] (2019): Thyroid disease: assessment and management. Endorses Levothyroxine monotherapy.
- BTA (British Thyroid Association): Guidelines on hypothyroidism management.
- ATA (American Thyroid Association): Guidelines for hypothyroidism and pregnancy. Strong emphasis on strict TSH control in pregnancy (<2.5 in 1st trimester).
- Cochrane Reviews: Consistently show no benefit of T3/T4 combination therapy over T4 alone for general wellbeing.
What is Hashimoto's Thyroiditis? It is a condition where your own immune system mistakenly attacks your thyroid gland (a butterfly-shaped gland in your neck). Over time, this damages the gland so it can't make enough thyroid hormone.
What are the symptoms? Because thyroid hormone runs your body's "engine" (metabolism), lack of it slows everything down. You might feel tired, gain weight, feel cold when others are warm, comprise dry skin, and have constipation.
Is there a cure? We cannot "cure" the immune attack, but we can easily replace the missing hormone. You will take a daily tablet called Levothyroxine. This is identical to the hormone your thyroid used to make.
How do I take the tablet?
- Take it first thing in the morning.
- Wait at least 30 minutes before eating or drinking coffee.
- This helps your body absorb it properly.
What if I want to get pregnant? It is very safe to take Levothyroxine during pregnancy—in fact, it is vital for your baby's brain development. You will likely need a higher dose when you are pregnant, so tell your doctor immediately if you have a positive test.
- NICE. Thyroid disease: assessment and management [NG145]. 2019.
- Okosieme F, et al. Management of primary hypothyroidism: statement by the British Thyroid Association Executive Committee. Clin Endocrinol (Oxf). 2016;84(6):799-808.
- Alexander EK, et al. 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum. Thyroid. 2017;27(3):315-389.
- Chaker L, et al. Hypothyroidism. Lancet. 2017;390(10101):1550-1562.