Hashimoto Thyroiditis
I. The "On-Call" Snapshot
Clinical Significance in Malaysia: This is the most common cause of primary hypothyroidism in our population, especially among adult women. You will manage this constantly in primary care, medical clinics, and when admitting patients for other issues.
High-Yield Definition: "Hashimoto's thyroiditis is a chronic autoimmune disease in which T-cell mediated and autoantibody-mediated processes lead to the destruction of thyroid follicular cells, resulting in gradual and progressive thyroid failure." (Source: UpToDate, 2024).
Clinical One-Liner: Autoimmune hypothyroidism in a middle-aged woman presenting with a non-tender goitre and symptoms of metabolic slowdown.
II. Etiology & Risk Factors
Etiology: Autoimmune destruction of the thyroid gland. It's a combination of genetic susceptibility and environmental triggers.
Risk Factors:
Female sex (approx. 8:1 ratio)
Age (peak 30-50 years)
Family history of thyroid or other autoimmune diseases
Co-existing autoimmune conditions (Type 1 DM, pernicious anaemia, Addison's disease, vitiligo)
High dietary iodine intake (can paradoxically trigger autoimmunity in susceptible individuals)
III. Quick Pathophysiology
It's straightforward. Your own immune system gets confused.
T-lymphocytes infiltrate the thyroid gland. They think your thyrocytes are foreign.
These T-cells kill the thyrocytes (cytotoxic T-cell mediated cell death).
B-cells produce antibodies, primarily anti-thyroid peroxidase (Anti-TPO) and anti-thyroglobulin (Anti-Tg). These contribute to the destruction.
As thyrocytes are destroyed, thyroid hormone (T4/T3) production falls.
The pituitary gland senses this and pumps out more TSH to compensate. This TSH stimulation is what causes the goitre.
Eventually, the gland fails, T4 drops despite high TSH, and the patient becomes overtly hypothyroid.
IV. Classification
We don't "stage" Hashimoto's like a cancer. We classify it based on the patient's thyroid function at the time of presentation:
Euthyroid: Goitre and/or positive antibodies are present, but TSH and fT4 are normal. Patient is asymptomatic.
Subclinical Hypothyroidism: TSH is elevated, but fT4 is still within the normal range. The gland is failing but still compensating. Patient may be asymptomatic or have mild symptoms.
Overt Hypothyroidism: TSH is high and fT4 is low. The gland can no longer compensate. Patient is symptomatic.
V. Clinical Assessment
🚩 Red Flags & Immediate Actions
Altered Mental Status/Coma + Hypothermia + Bradycardia: This is Myxoedema Coma.
Action: Alert your senior/specialist immediately. Secure ABCs, start IV Hydrocortisone 100mg STAT, followed by loading dose of IV Levothyroxine. This patient needs ICU admission.
Reason: It's a state of severe decompensated hypothyroidism with a mortality rate of 30-50%.
Stridor or Severe Dysphagia: Suggests a large goitre causing tracheal or oesophageal compression.
Action: Assess airway. Keep patient sitting up. Inform senior and get an urgent ENT consult. Prepare for imaging (CT neck).
Reason: Potential for acute airway compromise.
History
Key Diagnostic Clues: A middle-aged woman complaining of feeling tired and "slow" for months, with a painless lump in her neck.
Symptom Breakdown:
Common (>50%): Fatigue, lethargy, cold intolerance, weight gain (usually mild, 2-5kg), constipation, dry skin, hair loss.
Less Common (10-50%): Menstrual irregularities (menorrhagia), myalgia, arthralgia, depression, poor concentration, hoarseness of voice.
Rare (<10%): Carpal tunnel syndrome, psychosis ("myxoedema madness").
Pertinent Negatives: Ask about palpitations, heat intolerance, weight loss (to rule out hyperthyroidism). Ask about neck pain or fever (to rule out subacute thyroiditis).
Physical Examination (OSCE Approach)
General Inspection: May appear lethargic. Look for facial puffiness (periorbital oedema), thinning hair, and loss of the outer third of eyebrows (Hertoghe's sign).
Vitals: Bradycardia is common. Blood pressure can be normal or low. Hypothermia in severe cases.
Disease-Specific Examination (Neck):
Inspection: Visible goitre.
Palpation: The goitre is characteristically diffuse, firm, rubbery, and non-tender. The surface may feel bosselated (lumpy). Pemberton's sign is negative unless the goitre is massive and retrosternal.
Positive Findings:
Skin: Cool, dry, pale.
Neurology: Delayed relaxation phase of deep tendon reflexes (e.g., ankle jerk). This is a classic sign (Woltman's sign).
Cardiovascular: Muffled heart sounds (due to pericardial effusion in severe cases).
Pertinent Negatives: No proptosis, ophthalmoplegia, or pretibial myxoedema (these are signs of Graves' disease). No thyroid bruit.
Clinical Pearl: If a patient has a goitre but their TFT is normal, check the Anti-TPO. If it's high, you've found euthyroid Hashimoto's. They will likely become hypothyroid in the future, so they need follow-up.
VI. Diagnostic Workflow
Differential Diagnosis
Iodine Deficiency Goitre:
Points For: Goitre, potential hypothyroidism.
Points Against: Less common in Malaysia due to universal salt iodization. Antibodies are negative.
How to Differentiate: Negative Anti-TPO antibodies.
Graves' Disease:
Points For: Autoimmune, goitre.
Points Against: Patient is hyperthyroid (tachycardia, weight loss, tremor).
How to Differentiate: TFT shows suppressed TSH, high fT4. TRAb is positive.
Subacute (de Quervain's) Thyroiditis:
Points For: Goitre, transient thyroid dysfunction.
Points Against: Presents with a very painful, tender neck, often after a viral URI.
How to Differentiate: History of neck pain, tender goitre on palpation, and a markedly elevated ESR/CRP.
Investigations Plan
Bedside: None.
First-Line Labs:
Thyroid Function Test (TSH, Free T4): This is the essential first step. Expect ↑ TSH, ↓ or normal fT4.
Anti-TPO Antibody: This is the key test to confirm the autoimmune etiology. Titres are usually very high (>100 IU/mL). Anti-Tg can also be checked but is less sensitive.
Confirmatory / Gold Standard: A high Anti-TPO titre in the context of primary hypothyroidism is diagnostic. FNAC or biopsy is not needed unless a suspicious nodule is found on ultrasound that requires investigation to rule out malignancy (e.g., papillary thyroid cancer or lymphoma).
VII. Staging & Severity Assessment
Severity is based on biochemistry, which guides treatment decisions.
Subclinical Hypothyroidism: TSH > 4.5 mIU/L but < 10 mIU/L, with a normal Free T4. Treatment is considered if TSH is persistently >10, the patient is symptomatic, pregnant, or has a large goitre.
Overt Hypothyroidism: TSH > 10 mIU/L with a low Free T4. Treatment is always indicated.
VIII. Management Plan
A. Principle of Management:
Replace the deficient thyroid hormone with oral levothyroxine. The goal is to restore the patient to a clinical and biochemical euthyroid state, resolving their symptoms.
B. Immediate Stabilisation (ABCDE Plan):
Not applicable unless the patient is in myxoedema coma.
C. Definitive Treatment (The Ward Round Plan):
First-Line: Levothyroxine (L-thyroxine).
Dosing:
Young, healthy adults: Start with a near-full replacement dose, calculated at 1.6 mcg/kg/day. (e.g., a 60kg patient would get ~100mcg daily).
Elderly (>65 years) or patients with ischaemic heart disease: Start low and go slow. Begin with 12.5-25 mcg daily.
Titration & Monitoring:
Recheck TSH 6-8 weeks after starting or changing a dose.
Adjust the dose by 12.5-25 mcg increments based on the TSH result.
Target TSH: 0.5 - 2.5 mIU/L.
Crucial Patient Counselling:
Take the tablet once daily on an empty stomach, ideally 30-60 minutes before breakfast.
Do not take it with coffee, or with supplements like iron or calcium, as they impair absorption. Separate these by at least 4 hours.
This is usually lifelong therapy.
D. Long-Term & Discharge Plan:
Once TSH is stable, monitor annually with a TFT.
Educate the patient on the symptoms of both hypothyroidism and hyperthyroidism (iatrogenic).
Inform them that dose requirements increase during pregnancy and they must seek medical advice as soon as they know they are pregnant.
IX. Complications
Short-Term: Hashitoxicosis (a transient hyperthyroid phase early in the disease due to hormone leakage from dying cells).
Long-Term:
Cardiovascular: Dyslipidaemia, hypertension, and increased risk of IHD if left untreated.
Obstetric: Infertility, miscarriage, pre-term delivery in untreated mothers.
Malignancy: Small but increased risk of Primary Thyroid Lymphoma (specifically MALT lymphoma). Suspect this if a long-standing goitre suddenly begins to enlarge rapidly.
X. Prognosis
Excellent. With proper levothyroxine replacement and adherence, patients have a normal quality of life and life expectancy. The main factor affecting prognosis is patient compliance.
XI. How to Present to Your Senior
Use the SBAR format. Be concise.
(Situation): "Dr, I'm calling about Madam Z, a 45-year-old lady I just saw in the clinic with newly suspected hypothyroidism."
(Background): "She presented with a 6-month history of fatigue, constipation, and a painless neck swelling. She has a family history of thyroid problems. No IHD or other chronic illnesses."
(Assessment): "On examination, she has a diffuse, firm, non-tender goitre, Grade 2. Her ankle jerks show delayed relaxation. My primary diagnosis is Hashimoto's thyroiditis with overt hypothyroidism."
(Recommendation): "My plan is to send a TFT and Anti-TPO antibody test today. I would like to start her on Levothyroxine 75 mcg once daily and arrange to see her again in 6 weeks with the results to titrate the dose. Does that sound reasonable?"
XII. Summary & Further Reading
Top 3 Takeaways:
Hashimoto's is the number one cause of hypothyroidism with goitre in our setting. Think of it in any patient with fatigue and non-specific "slowing down" symptoms.
Diagnosis is confirmed with a high TSH and a positive Anti-TPO antibody.
Treatment is lifelong Levothyroxine, dosed based on weight and comorbidities, and titrated against TSH every 6-8 weeks until stable.
Key Resources:
UpToDate: Search for "Hashimoto's thyroiditis" and "Treatment of primary hypothyroidism in adults". This should be your primary resource.
Amboss: Search "Hashimoto's thyroiditis". Excellent for quick review and diagnostics.
StatPearls: "Hashimoto Thyroiditis". Good for a detailed overview.
