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Difficulty: MediumEndocrinology and Metabolism

Match each etiology of thyrotoxicosis to its characteristic laboratory and radioactive iodine uptake (RAIU) diagnostic profile.

  • Graves diseaseDecreased TSH, increased Free T4, diffusely increased RAIU
  • Exogenous thyroid hormone intakeDecreased TSH, increased Free T4, decreased RAIU, decreased serum thyroglobulin
  • Subacute (granulomatous) thyroiditisDecreased TSH, increased Free T4, decreased RAIU, increased serum thyroglobulin
  • Toxic multinodular goiterDecreased TSH, increased Free T4, heterogeneous (patchy) increased RAIU

Answer

Graves disease matches with diffusely increased RAIU; Exogenous thyroid hormone matches with decreased RAIU and decreased thyroglobulin; Subacute thyroiditis matches with decreased RAIU and increased thyroglobulin; Toxic multinodular goiter matches with heterogeneous (patchy) increased RAIU.
The matching correctly pairs each underlying pathophysiology with its diagnostic hallmark. RAIU maps the gland's synthetic activity, separating hyper-synthesizing disorders from destructive/exogenous ones. Thyroglobulin further differentiates endogenous destructive processes (high) from exogenous hormone suppression (low).

Step-by-Step Solution

1
Confirm the presence of thyrotoxicosis.
All profiles demonstrate decreased TSH and increased Free T4.
This establishes the primary biochemical state before differentiating the underlying cause.
2
Evaluate the radioactive iodine uptake (RAIU) pattern.
RAIU distinguishes conditions with increased hormone synthesis (high uptake) from those with hormone release/exogenous sources (low uptake).
High/normal uptake points to Graves or toxic nodular disease. Low uptake points to thyroiditis, iodine load, or exogenous sources.
3
Differentiate high RAIU conditions by uptake distribution.
Diffuse uptake indicates Graves disease, whereas patchy/heterogeneous uptake indicates toxic multinodular goiter.
Graves involves global gland stimulation by antibodies, whereas TMNG involves localized autonomous nodules.
4
Differentiate low RAIU conditions using serum thyroglobulin.
High thyroglobulin indicates thyroiditis (follicular destruction), whereas low thyroglobulin indicates exogenous intake.
Thyroglobulin is co-secreted with endogenous thyroid hormone. Its absence confirms the thyrotoxicosis is from an external source.

Key Concept

Differentiation of thyrotoxicosis etiologies using radioactive iodine uptake (RAIU) and serum thyroglobulin levels.
Estimated Time:1m 30s
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Topics

Endocrinology and Metabolism

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