Hypothyroidism

The Hypothalamic-Pituitary-Thyroid (HPT) Axis

Classification

• Goldman-Cecil Medicine, p. 2433

Causes

Primary Hypothyroidism

Secondary (Central) Hypothyroidism

Hashimoto Thyroiditis (Chronic Lymphocytic Thyroiditis)

• CD8+ cytotoxic T cells kill thyroid epithelial cells directly
• Cytokines (IFN-γ, TNF) from activated T cells induce apoptosis via Fas-FasL pathway
• Anti-TPO (thyroid peroxidase) and anti-thyroglobulin antibodies are present in nearly all patients - TPO-Ab titers predict progression to overt hypothyroidism
• Autoimmune risk is highly heritable (variants in immunomodulatory genes)

Clinical Features of Hypothyroidism

Diagnosis

• In primary hypothyroidism: TSH is elevated because loss of T4/T3 removes negative feedback on TRH and TSH
• In central hypothyroidism: TSH is low or inappropriately normal despite low T4
• Serum T4 (free T4): decreased in overt hypothyroidism of any cause
• TPO-Ab: confirms autoimmune etiology; elevated in >95% of Hashimoto thyroiditis
• Pitfalls to be aware of (Goldman-Cecil Table 207-1):
  • Biotin supplementation (>100 mg/day): artificially lowers TSH, elevates T4/T3 - resolves after stopping biotin 2-3 days
  • Heterophile antibodies: artificially raise TSH
  • Macro-TSH: elevated TSH but bioinactive - use polyethylene glycol precipitation to detect

Treatment

Overt Hypothyroidism

• Average replacement dose: 1.6 µg/kg/day orally
• Start lower (25-50 µg/day) in elderly patients and those with cardiac disease; titrate upward every 4-6 weeks
• Goal: TSH in the normal reference range (0.5-2.5 mIU/L for most patients)
• Monitor TSH annually once stable
• Take on empty stomach; separate from calcium, iron, cholestyramine (absorption interference)

Combination T4/T3 Therapy

Subclinical Hypothyroidism

• TSH >10 mIU/L: L-T4 treatment reasonable - may reduce LDL cholesterol; no symptom benefit in elderly (>65 years)
• TSH 5-10 mIU/L: Consider treating if symptoms are present OR elevated TPO-Ab titers
• Otherwise: recheck TSH and free T4 annually

Hypothyroidism in Pregnancy

• L-T4 dose requirement increases by 25-50% during pregnancy (increased TBG, fetal demand, placental metabolism)
• A practical approach: increase from 7 tablets/week to 9 tablets/week as soon as pregnancy is confirmed
• Target TSH: <2.5 mIU/L throughout gestation
• Check TSH every 4 weeks until mid-gestation
• Untreated hypothyroidism in early pregnancy is linked to impaired fetal neurological development

Myxedema Coma

• IV L-T4: loading dose 200-300 µg IV, then 1.6 µg/kg IV every 24 hours
• IV T3: 5-10 µg every 8-12 hours (added because T4→T3 conversion is impaired)
• IV hydrocortisone: 100 mg every 6 hours until adrenal insufficiency excluded (concurrent adrenal insufficiency is common)
• Passive rewarming only - active rewarming worsens hypotension

Special Populations and Considerations

Congenital Hypothyroidism

• Incidence: 1 in 3,500 births
• Causes: thyroid dysgenesis, dyshormonogenesis, or severe iodine deficiency
• Consequences: devastating irreversible neurological damage ("cretinism") if untreated
• Neonatal TSH screening programs have dramatically reduced impact

Drug-Induced Hypothyroidism

Thyroiditis Summary Table

Recent Evidence (2024-2026)

• A 2025 systematic review (PMID 40446861) in Complementary Therapies in Medicine found long-term exercise-based interventions may modestly improve thyroid function in hypothyroid patients, though evidence remains limited.
• A 2026 meta-analysis (PMID 42095176) identified predictors of permanent hypothyroidism after subacute thyroiditis.
• A 2025 meta-analysis (PMID 40609565) in Lancet Diabetes & Endocrinology examined links between gestational thyroid function/autoimmunity and gestational diabetes.

• Goldman-Cecil Medicine International Edition, pp. 2431-2436
• Robbins & Kumar Basic Pathology, pp. 729-731
• Textbook of Family Medicine 9e, pp. 1021-1022

Is Levothyroxine Lifelong in Hashimoto's? - Not Always

The Key Distinction: What Are You Treating?

Spontaneous Remission is Real (in ~10% of Cases)

"Hypothyroidism resulting from Hashimoto thyroiditis is transient in approximately 10% of cases. Spontaneous remission is associated with the presence of a larger goiter, a high initial TSH level, and a family history of thyroid disease."

The Problem of Overuse and Deprescribing

• Levothyroxine is one of the most overprescribed medications in the US
• Many patients are started on it for mild subclinical hypothyroidism or non-evidence-based indications (e.g., weight gain, depression in euthyroid individuals)
• High-certainty evidence does NOT show benefit of levothyroxine in subclinical hypothyroidism for quality of life or symptom outcomes
• Once started, it is continued lifelong for most patients - even when not warranted
• The paper argues for "deprescribing" - a structured, supervised withdrawal of levothyroxine in selected patients where it is no longer necessary or never was

When Levothyroxine IS Lifelong

1. Overt hypothyroidism (low FT4, markedly elevated TSH) - especially with symptoms
2. Advanced gland destruction - ultrasound showing severe fibrosis/atrophy with negligible residual tissue
3. Post-thyroidectomy or post-radioiodine (not Hashimoto per se, but often co-exists)
4. Pregnancy history of dose requirements confirms significant gland failure
5. Persistently positive TPO-Ab with progressive TSH rise over serial testing - predicts irreversible failure

"As [Hashimoto's] progresses, more functioning thyroid gland becomes fibrotic, and less indigenous T4 is produced. After diagnosis, replacement doses of T4 should be used... Serum TSH is followed annually to ensure adequate control."

Practical Clinical Approach

1. Periodic reassessment is mandatory - TSH annually even in stable patients
2. If TSH normalizes on a low L-T4 dose, consider a supervised trial of dose reduction or discontinuation with close TSH monitoring (every 6-8 weeks initially)
3. Do not assume lifelong need simply because Hashimoto's is the diagnosis - titrate to the thyroid function, not the antibody status
4. Antibody titers alone (TPO-Ab, TgAb) are not an indication for treatment in a euthyroid patient
5. For subclinical hypothyroidism (TSH 5-10 mIU/L), guidelines suggest treatment only if TSH >10, or if symptomatic, or if pregnant - not reflexively lifelong in all cases

Bottom Line

• Cummings Otolaryngology Head and Neck Surgery, p. 2717
• Textbook of Family Medicine 9e, p. 1022
• Maraka S & Papaleontiou M. "Approach to the Patient Considering Thyroid Hormone Deprescribing." J Clin Endocrinol Metab, 2026 (PMID: 41482002)

• TSH: 11.7 µIU/mL (ref: 0.38-5.33) - elevated
• fT4: 0.7 ng/dL (ref: 0.58-1.64) - low-normal (within range but toward the lower end)
• Anti-TPO: 116.99 IU/mL (ref: <5.61) - markedly elevated (~20x upper limit)
• Anti-Tg: 4.08 IU/mL (ref: <4.11) - borderline normal
• Patient: Thanusree, 20-year-old female, Government Stanley Medical College / Dr. Stanley Hospital, Chennai

Interpretation

Important Nuances for This Specific Patient

1. This is Subclinical Hypothyroidism (borderline overt)

• TSH at 11.7 is above the "subclinical" threshold of 10 mIU/L - this is the zone where treatment benefit becomes clearer
• fT4 is still technically within range, but sitting low-normal - the pituitary compensation is working but barely

2. Age and sex matter

• 20-year-old female: high prior probability of autoimmune thyroid disease (female:male = 10:1 to 20:1)
• At this age with active autoimmune destruction and TSH >10, treatment with levothyroxine is recommended - this is not the elderly patient where benefit is uncertain

3. Anti-Tg adds little here

• Anti-Tg (4.08 vs ref <4.11) is essentially normal
• Anti-TPO alone is sufficient to diagnose Hashimoto's - and it is very clearly positive here

4. What "autoimmune" does NOT automatically mean

• It does not tell you the degree of gland destruction yet - a thyroid ultrasound would help (heterogeneous echotexture, hypoechogenicity, increased vascularity are typical in Hashimoto's)
• Anti-TPO positivity alone in a euthyroid individual does not require treatment - but this patient is not euthyroid (TSH 11.7)

Bottom Line for Thanusree

Honest Answer: Stopping Levothyroxine in Hashimoto's

The Short Answer

Why Stopping is Unlikely in Most Hashimoto's Patients

• Destroyed thyroid tissue does not regenerate. Once follicles are replaced by fibrosis, that functional mass is gone permanently.
• The disease generally progresses over decades - meaning the thyroid makes less and less hormone over time, not more.
• A young patient (20 years old) with already-elevated TSH and high Anti-TPO is at an early-to-mid stage of this process. Without treatment, it will worsen, not reverse.
• Annual TSH monitoring in Hashimoto's patients shows a 4-5% per year progression rate from subclinical to overt hypothyroidism.

The ~10% Who Can Stop

"Hypothyroidism resulting from Hashimoto thyroiditis is transient in approximately 10% of cases. Spontaneous remission is associated with: a larger goiter, a high initial TSH level, and a family history of thyroid disease."

What "Deprescribing" Research Says (2026)

• Levothyroxine is one of the most overprescribed drugs in the world
• Many patients are started unnecessarily and stay on it lifelong without re-evaluation
• Structured, supervised withdrawal IS feasible and safe in selected patients
• The key selected patients are those with: mild subclinical hypothyroidism at initiation, or who were started for non-evidence-based reasons

What Actually Helps Reduce the Autoimmune Burden

The Most Realistic Path Forward for Thanusree

The Honest Message for the Patient

"The tablet replaces what your thyroid is no longer making - it is not a drug that treats the disease itself. For most people with Hashimoto's, the thyroid makes progressively less hormone over the years, which means the tablet becomes more necessary with time, not less. About 1 in 10 patients do see their thyroid recover, but we cannot predict this at the start. What we can do is check your thyroid function every year, and if your TSH ever normalizes on a very small dose, we can try - carefully and under supervision - to reduce or stop the tablet. Right now, at age 20 with these results, the tablet is protecting your brain, heart, and reproductive health. It is a very safe medication and does not cause side effects when the dose is right."