What thyroid study results are expected in a patient with a suspected toxic thyroid adenoma, presenting with hyperthyroidism symptoms, a palpable thyroid nodule, and normal vitals, including Thyroid-Stimulating Hormone (TSH), thyroglobulin, and Radioactive Iodine Uptake (RAIU) tests?

Thyroid Study Results in Toxic Thyroid Adenoma

The correct answer is C: Low TSH, High Thyroglobulin, Focal uptake on RAIU.

Explanation of the Diagnosis

The patient presents with classic symptoms of hyperthyroidism (palpitations, heat intolerance, increased urination, weight loss) and has a palpable thyroid nodule. This clinical picture is most consistent with a toxic thyroid adenoma (also called autonomous functioning thyroid nodule).

Expected Laboratory Findings:

1. TSH: Low

   • In toxic adenoma, the autonomous nodule produces thyroid hormone independently of TSH regulation, causing suppression of TSH 1

2. Thyroglobulin: High

   • Thyroglobulin is typically elevated in toxic adenomas due to increased production by the hyperfunctioning nodule 2

3. RAIU (Radioactive Iodine Uptake): Focal uptake

   • The hallmark finding in toxic adenoma is focal uptake of radioiodine in the hyperfunctioning nodule with suppression of the surrounding normal thyroid tissue 1, 3

Differential Diagnosis

Why not the other options?

• Option A (High TSH, Low Thyroglobulin, Low RAIU): This pattern suggests hypothyroidism, not hyperthyroidism 1

• Option B (Low TSH, High Thyroglobulin, Diffuse uptake): This pattern is typical for Graves' disease, which presents with diffuse uptake on RAIU scan rather than focal uptake 3

• Option D (Low TSH, High Thyroglobulin, Low RAIU): This pattern is seen in thyroiditis or exogenous thyroid hormone ingestion 1

• Option E (Low TSH, Low Thyroglobulin, Low RAIU): This pattern suggests factitious hyperthyroidism (thyroid hormone ingestion) 1

Clinical Correlation

The patient's presentation aligns perfectly with toxic adenoma:

• Middle-aged patient (52 years)
• Hyperthyroid symptoms (palpitations, heat intolerance, increased urination, weight loss)
• Palpable nodule (1 cm in left upper lobe of thyroid)
• No eye or skin findings (which would suggest Graves' disease)
• Normal vitals (suggesting mild to moderate hyperthyroidism)

Management Implications

Understanding the correct pattern of laboratory findings is crucial for appropriate management:

1. Confirmation of diagnosis: The focal uptake on RAIU confirms toxic adenoma and rules out other causes of hyperthyroidism 1

2. Treatment options:

   • Radioactive iodine therapy: Effective with 77-93% success rate after a single dose 4, 5
   • Surgery (lobectomy)
   • Thermal ablation for selected cases 1, 2

3. Monitoring:

   • Follow-up should include thyroid function tests at 3,6, and 12 months 2
   • Ultrasound to monitor nodule size reduction (expect approximately 54% reduction within 12 months after radioiodine therapy) 4

Key Points to Remember

• Toxic adenoma accounts for approximately 13-14% of hyperthyroidism cases 3
• The pattern of low TSH, high thyroglobulin, and focal uptake on RAIU is diagnostic
• Risk of post-treatment hypothyroidism is lower with toxic adenoma (10.3%) compared to Graves' disease 4, 5
• Rare complications include development of TSH receptor antibodies after radioiodine therapy 6

The laboratory pattern in option C (Low TSH, High Thyroglobulin, Focal uptake) is the only one consistent with the clinical presentation of toxic thyroid adenoma.