What caused the physician to miss the correct diagnosis of autoimmune thyroiditis (Hashimoto's thyroiditis) in a patient with hypothyroidism?

What Caused the Physician to Miss the Correct Diagnosis

The physician likely relied solely on initial TSH testing without checking thyroid antibodies (anti-thyroid peroxidase and anti-thyroglobulin antibodies), which are essential to distinguish autoimmune thyroiditis (Hashimoto's) from other causes of hypothyroidism.

The Core Diagnostic Error

The physician made Option B the primary error—depending on initial investigation alone. Here's why this matters clinically:

Why Antibody Testing is Critical

• Hashimoto's thyroiditis is diagnosed by the presence of elevated thyroid peroxidase (TPO) and thyroglobulin antibodies, not just by TSH elevation 1, 2
• Approximately 25% of patients with type 1 diabetes have thyroid autoantibodies at diagnosis, and TPO antibodies are more predictive than thyroglobulin antibodies for autoimmune thyroid disease 1
• Guidelines explicitly recommend testing for anti-thyroid peroxidase and anti-thyroglobulin antibodies soon after diagnosis to identify autoimmune etiology 1

The Clinical Implications of Missing This Diagnosis

Hashimoto's thyroiditis has distinct management considerations beyond simple hypothyroidism:

• Patients with Hashimoto's are at increased risk for other organ-specific and non-organ-specific autoimmune disorders 3
• Even with normal TSH levels (euthyroid Hashimoto's), patients may experience persistent symptoms including neuropsychological deficits, decreased cardiac performance, and fibromyalgia 3
• Hashimoto's patients require surveillance for progression to overt hypothyroidism, as approximately 37% of subclinical hypothyroidism cases may revert to euthyroid state, but autoimmune cases typically progress 1

The Systematic Approach That Was Needed

While Option A (lack of systematic approach) contributed, the specific failure was incomplete initial workup:

Complete Initial Evaluation Should Include:

1. TSH measurement (the screening test) 1
2. Thyroid antibody testing (TPO and thyroglobulin antibodies) to identify autoimmune etiology 1, 2
3. Clinical assessment for goiter and symptoms 2
4. Thyroid ultrasound if indicated, though imaging alone cannot differentiate causes of hypothyroidism 1

Common Pitfall to Avoid

The ACR Appropriateness Criteria explicitly state there is no role for imaging in the workup of hypothyroidism in adults, as imaging for thyroid morphology does not help differentiate among causes 1. The diagnosis of Hashimoto's is made biochemically with antibody testing, not radiologically.

Why This Matters for Treatment

• Patients with confirmed Hashimoto's thyroiditis may have poor response to levothyroxine despite normal TSH levels due to persistent autoimmune activity 4
• These patients require monitoring for other autoimmune conditions including celiac disease, which occurs in higher frequency 1
• Lifelong thyroid hormone replacement is typically necessary in Hashimoto's, whereas other causes of hypothyroidism may be transient 2, 5

The answer is B—the physician depended on initial investigation (TSH alone) without completing the diagnostic workup with antibody testing to confirm the autoimmune etiology.