```html

Radiation‑Induced Thyroiditis

Overview

Radiation‑induced thyroiditis (RIT) is an inflammatory condition of the thyroid gland that occurs after exposure to ionizing radiation. The inflammation may be acute (within weeks to months) or sub‑acute/chronic (months to years) after therapeutic or occupational radiation exposure. The thyroid is one of the most radiosensitive endocrine organs because it actively traps iodine and concentrates radiation doses.

Who it affects

• Patients who have received head‑and‑neck radiation for cancers such as lymphoma, nasopharyngeal carcinoma, or thyroid cancer.
• Individuals treated with radioactive iodine (RAI) therapy for hyperthyroidism or differentiated thyroid carcinoma.
• Survivors of childhood cancers who received cranial or neck irradiation.
• Rarely, workers exposed to high‑dose occupational radiation (e.g., nuclear plant accidents).

Prevalence

• Acute thyroiditis occurs in 5–10% of patients receiving neck irradiation for head‑and‑neck cancers.
• Long‑term hypothyroidism, a sequela of thyroiditis, develops in 20–40% of irradiated patients after 5 years.
• After radioactive iodine therapy for Graves’ disease, transient thyroiditis is reported in 15–30% of patients.

Symptoms

Symptoms reflect inflammation and, later, impaired hormone production. The presentation can be divided into an acute “painful” phase and a chronic “hypothyroid” phase.

Acute/Sub‑Acute Phase (days–weeks)

• Neck pain or tenderness – often radiates to the jaw, ears, or upper chest and worsens with swallowing.
• Swelling or fullness of the thyroid region; may be palpable as a tender goiter.
• Fever and malaise – low‑grade fever (≤38.5 °C) is common.
• Thyrotoxic symptoms (due to leakage of stored hormones):
  • Palpitations, tachycardia
  • Anxiety, irritability
  • Heat intolerance, sweating
  • Weight loss despite normal appetite
• Voice changes – hoarseness if the recurrent laryngeal nerve is irritated.
• Difficulty swallowing (dysphagia) if severe edema compresses the esophagus.

Chronic Phase (months–years)

• Hypothyroid symptoms due to glandular destruction:
  • Fatigue, sluggishness
  • Weight gain, cold intolerance
  • Constipation, dry skin
  • Depressed mood, memory problems
• Persistent neck fullness or a non‑tender goiter.
• Rarely, autoimmune thyroiditis may develop, presenting with positive antimicrosomal antibodies.

Causes and Risk Factors

Radiation damages thyroid follicular cells, leading to:

• Direct DNA injury → cell death and inflammatory cytokine release.
• Vascular endothelial damage → edema and hemorrhage.
• Release of pre‑formed thyroid hormones into the bloodstream, causing transient thyrotoxicosis.

Key risk factors

• Higher cumulative radiation dose (≥30 Gy for external beam, ≥150 mCi for radioactive iodine).
• Younger age – children’s thyroid tissue is more radiosensitive.
• Female sex – women are twice as likely to develop post‑radiation thyroid dysfunction.
• Pre‑existing thyroid disease (e.g., Graves’ disease, nodular goiter).
• Concurrent chemotherapy – may augment radiation injury.
• Short distance between radiation field and the thyroid (e.g., neck extensions in head‑and‑neck cancer protocols).

Diagnosis

Diagnosis is clinical, supported by laboratory and imaging studies that differentiate radiation‑induced thyroiditis from other thyroid disorders.

1. History & Physical Exam

• Timing of symptom onset relative to radiation exposure.
• Presence of neck tenderness, swelling, or radiation dermatitis.
• Assessment of thyroid size and tenderness on palpation.

2. Laboratory Tests

• Thyroid function tests (TFTs) – TSH, free T4, free T3.
  • Acute phase: low/normal TSH with elevated free T4/T3 (thyrotoxic).
  • Chronic phase: elevated TSH with low free T4/T3 (hypothyroid).
• Inflammatory markers – ESR and CRP may be modestly elevated during the painful phase.
• Thyroid antibodies – anti‑TPO or anti‑TG may appear if an autoimmune component develops.

3. Imaging

• Neck ultrasound – first‑line; shows diffuse hypoechogenicity, increased vascularity (hyperemia) in acute inflammation, or heterogeneous texture in chronic atrophy.
• Radioiodine uptake (RAIU) scan – markedly reduced uptake during acute thyroiditis, helping to distinguish from Graves’ disease (which shows high uptake).
• CT or MRI – reserved for large goiters causing airway compromise or to evaluate adjacent structures.

4. Biopsy (rare)

Fine‑needle aspiration (FNA) is only considered when nodules raise suspicion for malignancy, not for routine diagnosis of RIT.

Treatment Options

Treatment aims to control inflammation, manage hormone imbalances, and alleviate symptoms. Most cases are self‑limited, but interventions speed recovery and prevent complications.

1. Acute Painful Phase

• Non‑steroidal anti‑inflammatory drugs (NSAIDs) – ibuprofen 400‑600 mg q6‑8 h for 7‑10 days. Use gastro‑protection if needed.
• Corticosteroids – for severe pain or refractory inflammation: prednisone 40 mg daily, taper over 2‑3 weeks. Mayo Clinic.
• Beta‑blockers (e.g., propranolol 20‑40 mg q6‑8 h) to control tachycardia and tremor during transient thyrotoxicosis.
• Heat and neck support – warm compresses may provide comfort.

2. Thyrotoxic Phase Management

• Symptoms usually resolve within 4‑6 weeks as hormone stores deplete.
• Short‑term antithyroid drugs (PTU or methimazole) are generally NOT indicated because the excess hormone is not due to hypersecretion.

3. Chronic/Hypothyroid Phase

• Levothyroxine replacement – starting dose 1.6 µg/kg/day for adults, titrated to keep TSH within target (0.4‑4.0 mIU/L). Cleveland Clinic.
• Monitor TSH every 6‑8 weeks after dose changes, then every 6‑12 months once stable.
• Adjunctive calcium/vitamin D if radiation also damaged parathyroids.

4. Procedural Options (rare)

• Radiofrequency ablation or laser therapy for persistent, symptomatic nodules after radiation.
• Surgical thyroidectomy is reserved for:
  • Compressing goiter causing airway obstruction.
  • Suspicion of malignancy in a previously irradiated field.

5. Lifestyle & Supportive Care

• Maintain adequate hydration and a balanced diet rich in iodine (but not excessive).
• Regular gentle neck stretches to reduce stiffness.
• Stress‑reduction techniques (mindfulness, yoga) can lessen perception of pain.

Living with Radiation‑Induced Thyroiditis

Adapting daily life reduces discomfort and supports recovery.

Medication Adherence

• Take levothyroxine on an empty stomach, 30‑60 minutes before breakfast.
• Set a daily alarm or use a pill organizer.
• Inform any new prescriber that you are on thyroid medication; many drugs (e.g., iron, calcium, PPIs) interfere with absorption.

Monitoring

• Schedule thyroid function tests at the intervals recommended by your endocrinologist.
• Keep a symptom diary (pain, temperature, fatigue) to share with your provider.

Dietary Guidance

• Consume regular iodine sources (iodized salt, dairy, seafood) unless instructed otherwise.
• Avoid excessive soy, cruciferous vegetables, and gluten if they exacerbate hypothyroid symptoms—evidence is mixed but some patients report benefit.

Physical Activity

• Low‑impact aerobic exercise (walking, swimming) improves energy levels.
• Gentle neck range‑of‑motion exercises three times daily can prevent stiffness.

Emotional Well‑Being

• Join support groups for cancer survivors or thyroid disease (online communities, hospital‑run groups).
• Consider counseling if anxiety or depression develop—hypothyroidism can affect mood.

Prevention

While radiation therapy is often unavoidable, several strategies can reduce the risk or severity of thyroiditis.

During Radiation Planning

• Shielding – lead or tungsten shields placed over the thyroid when treating adjacent sites.
• Intensity‑modulated radiation therapy (IMRT) – allows precise dose sculpting, sparing thyroid tissue.
• Dose limitation – keep cumulative thyroid dose <30 Gy whenever possible (NCI guidelines).

Before Radioactive Iodine Therapy

• Assess baseline thyroid function; treat subclinical hyperthyroidism before RAI.
• Consider lower therapeutic activities for low‑risk disease.

Lifestyle Measures

• Maintain adequate nutritional iodine—deficiency increases susceptibility to radiation injury.
• Quit smoking; tobacco worsens radiation‑induced tissue inflammation.
• Control comorbidities (diabetes, hypertension) that can impair healing.

Complications

If radiation‑induced thyroiditis is not recognised or treated, several complications may arise:

• Permanent hypothyroidism – the most common long‑term outcome, requiring lifelong hormone replacement.
• Secondary hyperparathyroidism – from concurrent parathyroid damage, leading to calcium imbalance.
• Thyroid nodule formation – scar tissue can evolve into nodules; a small proportion become malignant, especially in previously irradiated fields.
• Airway obstruction – severe neck swelling can compress the trachea, a medical emergency.
• Cardiovascular stress – transient thyrotoxicosis may precipitate arrhythmias, especially in patients with underlying heart disease.

When to Seek Emergency Care

References

• American Thyroid Association. “Radiation Exposure and Thyroid Disease.” thyroid.org. Accessed 2026.
• Mayo Clinic. “Subacute Thyroiditis (De Quervain).” mayoclinic.org. 2023.
• Cleveland Clinic. “Hypothyroidism.” clevelandclinic.org. 2024.
• National Cancer Institute. “Radiation Therapy and Thyroid Toxicity.” cancer.gov. 2025.
• World Health Organization. “Iodine Deficiency.” who.int. 2022.
• National Institute of Diabetes and Digestive and Kidney Diseases. “Thyroid Disease.” nidkk.nih.gov. 2023.
• PubMed Central. “Incidence of thyroiditis after radioactive iodine therapy for Graves’ disease.” PMID 30663282. 2019.

```