Can Hashimoto's thyroiditis be the diagnosis?

Can Hashimoto's Thyroiditis Be the Diagnosis?

Yes, Hashimoto's thyroiditis can be the diagnosis if the patient presents with clinical features of hypothyroidism (or is euthyroid/hyperthyroid initially), has elevated thyroid peroxidase (TPO) antibodies and/or thyroglobulin antibodies, and demonstrates reduced echogenicity on thyroid ultrasound. 1

Epidemiology and Context

Hashimoto's thyroiditis (HT) is the most common autoimmune disease and the leading cause of hypothyroidism in industrialized nations. 2, 3, 4 It is the most frequent cause of hypothyroidism in pregnant and postpartum women in developed countries, while iodine deficiency remains the most common cause worldwide. 2

Clinical Presentation

Classic Presentation

HT presents with a spectrum of thyroid functional states:

• Most common initial presentations: 5

  • Subclinical hypothyroidism (39.5%)
  • Euthyroid state (36.5%)
  • Overt hypothyroidism (18.5%)
  • Less commonly: subclinical or overt hyperthyroidism (5.6% combined)

• Hypothyroid symptoms include: 2

  • Fatigue, muscle cramps, constipation
  • Cold intolerance, hair loss
  • With progression: voice changes, weight gain, intellectual slowness, insomnia
  • Advanced cases: myxedema (rare in pregnancy)

Important Clinical Variants

HT encompasses several clinico-pathologic entities beyond the classic form: 1

• Fibrous variant
• IgG4-related variant
• Juvenile form
• Hashitoxicosis (initial hyperthyroid phase)
• Painless thyroiditis (sporadic or postpartum)

Critical pitfall: Many patients with HT remain euthyroid or even present with hyperthyroidism initially due to the triphasic disease pattern (thyrotoxicosis → hypothyroidism → potential recovery). 3 Do not exclude HT based solely on normal or low TSH at presentation.

Diagnostic Criteria

Laboratory Confirmation

The diagnosis requires: 1

1. Elevated thyroid antibodies:

   • Anti-thyroid peroxidase (TPO) antibodies (most sensitive)
   • Anti-thyroglobulin antibodies
   • Both antibodies may be present

2. Thyroid function tests: 2

   • Initial screening: TSH is the recommended first test
   • Follow-up: TSH plus free T4 (FT4) or free thyroxine index (FTI)
   • Pattern depends on disease stage (elevated TSH with low/normal FT4 in hypothyroid phase)

3. Imaging findings: 1

   • Reduced echogenicity on thyroid ultrasound
   • Often demonstrates a painless goiter

Important consideration: Antibody levels may remain stable initially but can significantly decrease over time (by year 5 of follow-up). 5 However, diagnosis should not be delayed waiting for antibody trends.

Risk Factors Supporting the Diagnosis

Consider HT more strongly in patients with: 2

• Female sex
• Advancing age
• White race
• Type 1 diabetes
• Down syndrome
• Family history of thyroid disease
• Goiter
• Previous hyperthyroidism
• External-beam radiation to head/neck

Differential Considerations

Distinguish from Other Causes of Hypothyroidism

In pregnant/postpartum women, other common causes include: 2

• Subacute thyroiditis
• Radioactive iodine therapy (prior)
• Thyroidectomy (prior)
• Iodine deficiency

Distinguish from Hyperthyroidism

If patient presents with hyperthyroid symptoms: 2

• Graves' disease accounts for 95% of hyperthyroidism in pregnancy
• Distinctive features of Graves': eyelid lag/retraction, pretibial myxedema, elevated FT4 with suppressed TSH
• Hashitoxicosis (HT with initial hyperthyroid phase) is less common but possible 1

Key differentiator: Graves' disease can also be caused by Hashimoto thyroiditis in some cases, as both are autoimmune processes. 2 Check TSH receptor antibodies if Graves' disease is suspected clinically (ophthalmopathy, persistent hyperthyroidism). 2

Clinical Implications and Management Considerations

Disease Course

The natural history is dynamic: 5

• 48.4% of pediatric patients can be monitored without treatment
• Among those with overt hypothyroidism, 9% may become euthyroid and discontinue treatment
• Patients initially euthyroid or with subclinical hypothyroidism may progress to overt hypothyroidism requiring treatment

When to Treat

Initiate levothyroxine for: 2, 3

• Overt hypothyroidism (elevated TSH with low FT4)
• Symptomatic subclinical hypothyroidism
• Pregnant women with hypothyroidism (to prevent preeclampsia, low birth weight, and neurodevelopmental issues in offspring) 2

Monitoring without treatment is acceptable for: 5

• Euthyroid patients with positive antibodies
• Asymptomatic subclinical hypothyroidism (though this remains debated)

Special Populations

Pregnancy considerations: 2

• Untreated maternal hypothyroidism increases risk of preeclampsia
• Associated with low birth weight in neonates
• Severe iodine deficiency increases risk of congenital cretinism
• Screen pregnant women with symptoms or history of thyroid disease

Postpartum: 2

• Postpartum thyroiditis can occur within one year of delivery, miscarriage, or medical abortion
• Diagnosed by new onset of abnormal TSH and/or FT4
• May require antibody testing for confirmation
• Risk of permanent hypothyroidism is highest with elevated TSH and anti-TPO antibodies

Surveillance Requirements

All patients with HT require ongoing monitoring: 3, 5

• Regular clinical assessments
• Serial thyroid function testing (frequency based on treatment status and stability)
• Monitor for development of other autoimmune conditions 6
• Even euthyroid patients may develop symptoms and associated conditions independent of thyroid function

Common pitfall: Patients with normal TSH may still experience HT-related symptoms and associated autoimmune disorders. 6 Do not dismiss symptoms solely based on normal thyroid function tests in antibody-positive patients.