Can patients with Hashimoto's (thyroiditis) have normal thyroid function tests?

Patients with Hashimoto's Thyroiditis Can Have Normal Thyroid Function Tests

Yes, patients with Hashimoto's thyroiditis can have normal thyroid function tests, particularly in the early stages of the disease. Hashimoto's thyroiditis is an autoimmune disorder that can present with or without signs or symptoms of hypothyroidism, often with a painless goiter, and is associated with elevated thyroid peroxidase antibodies 1.

Diagnostic Findings in Hashimoto's Thyroiditis

• Hashimoto's thyroiditis is the most common cause of hypothyroidism in the United States, with risk factors including female sex, advancing age, white race, type 1 diabetes, Down syndrome, family history of thyroid disease, and goiter 2.

• While many patients with Hashimoto's thyroiditis develop hypothyroidism, a significant percentage can have normal thyroid function tests at diagnosis:

  • In a retrospective study of 153 children and adolescents with Hashimoto's thyroiditis, 47.1% were euthyroid at presentation 3.
  • Similarly, another study found that 36.7% of patients were euthyroid at baseline 4.

• The diagnosis of Hashimoto's thyroiditis is based on a combination of:

  • Presence of thyroid autoantibodies (anti-thyroid peroxidase [TPO] and/or anti-thyroglobulin [TG] antibodies)
  • Characteristic ultrasound findings (hypoechogenicity)
  • Clinical presentation 5

Natural Course of Hashimoto's Thyroiditis

• Hashimoto's thyroiditis often follows a progressive course:

  • Patients may initially be euthyroid with positive antibodies and normal TSH and T4 levels 3.
  • Over time, many patients progress to subclinical hypothyroidism (elevated TSH with normal free T4) 4.
  • Eventually, some patients develop overt hypothyroidism (elevated TSH with low free T4) 3, 4.

• In a study following children with Hashimoto's thyroiditis, 12 of 28 patients (43%) who were initially euthyroid developed subclinical or overt hypothyroidism within 18 months 4.

• The presence of TPO antibodies identifies an autoimmune etiology for thyroid dysfunction, with a higher risk of progression to overt hypothyroidism (4.3% per year vs. 2.6% per year in antibody-negative individuals) 6.

Diagnostic Approach

• The serum TSH test is the primary screening test for thyroid dysfunction. Multiple tests should be done over a 3-6 month interval to confirm or rule out abnormal findings 2.

• Follow-up testing of serum T4 levels in persons with persistently abnormal TSH levels can differentiate between subclinical (normal T4 levels) and "overt" (abnormal T4 levels) thyroid dysfunction 2.

• Testing for thyroid antibodies, particularly TPO antibodies, is helpful in confirming the diagnosis of Hashimoto's thyroiditis, even in patients with normal thyroid function tests 2.

• Thyroid ultrasound is seldom normal in patients with Hashimoto's thyroiditis, with one study finding that only 1.4% of patients had a normal thyroid ultrasound examination 7.

Management Considerations

• For patients with Hashimoto's thyroiditis and normal thyroid function tests (euthyroid):

  • Regular monitoring of thyroid function is recommended, as many patients will progress to hypothyroidism over time 3, 4.
  • The optimal monitoring interval is not clearly established, but checking thyroid function every 6-12 months is reasonable 6.

• Treatment with levothyroxine is generally recommended for:

  • Patients with overt hypothyroidism 1.
  • Patients with TSH >10 mIU/L, even with normal T4 levels 6.
  • For patients with TSH between 4.5-10 mIU/L, treatment decisions should be individualized based on symptoms and other factors 6.

• Some evidence suggests that levothyroxine treatment may have beneficial effects on thyroid antibody titers in patients with Hashimoto's thyroiditis 3, 4, 5.

Clinical Implications

• The presence of normal thyroid function tests does not rule out Hashimoto's thyroiditis, especially in patients with symptoms, goiter, or family history of thyroid disease 7.

• Patients with Hashimoto's thyroiditis and normal thyroid function should still be monitored periodically for the development of hypothyroidism 3, 1.

• Women planning pregnancy with Hashimoto's thyroiditis require special attention, as subclinical hypothyroidism during pregnancy is associated with adverse pregnancy outcomes 6.