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Difficulty: EasyEndocrinology and Metabolism

Match each classic laboratory profile to its most likely underlying pathophysiologic diagnosis.

  • Suppressed TSH, elevated free T4, positive thyrotropin receptor antibodiesGraves disease
  • Elevated TSH, decreased free T4, positive anti-thyroid peroxidase antibodiesHashimoto thyroiditis
  • Elevated serum calcium, elevated intact PTH, low serum phosphorus, normal creatininePrimary hyperparathyroidism
  • Decreased serum calcium, elevated intact PTH, elevated serum phosphorus, elevated serum creatinineSecondary hyperparathyroidism

Answer

The correct pairings match Graves disease with hyperthyroidism/TRAB positive, Hashimoto thyroiditis with hypothyroidism/anti-TPO positive, Primary hyperparathyroidism with hypercalcemia/hypophosphatemia, and Secondary hyperparathyroidism with hypocalcemia/hyperphosphatemia/renal failure.
The correct matches reflect the fundamental pathophysiological mechanisms of these classic endocrine disorders. Graves disease and Hashimoto thyroiditis represent primary thyroid disorders driven by distinct autoantibodies. Primary and secondary hyperparathyroidism are distinguished by the initial driving factor: autonomous parathyroid adenoma (causing hypercalcemia) versus chronic kidney disease (causing hypocalcemia, which stimulates PTH).

Step-by-Step Solution

1
Evaluate the thyroid function tests and specific autoantibodies.
A pattern of suppressed TSH and high free T4 with TRAB points to primary hyperthyroidism (Graves disease). A pattern of elevated TSH and low free T4 with anti-TPO points to primary hypothyroidism (Hashimoto thyroiditis).
Feedback loops dictate TSH levels based on free T4, while specific antibodies confirm the autoimmune etiology.
2
Evaluate the calcium, phosphorus, PTH, and creatinine levels.
High calcium and high PTH with low phosphorus indicates autonomous parathyroid overactivity (primary hyperparathyroidism). Low calcium, high phosphorus, and high creatinine with high PTH indicates a compensatory parathyroid response to renal failure (secondary hyperparathyroidism).
Differentiating primary from secondary parathyroid disorders relies on assessing whether PTH is driving the calcium abnormality or responding appropriately to it.

Key Concept

Interpretation of classical feedback loops and autoimmune markers in primary versus secondary endocrine disorders.
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Topics

Endocrinology and Metabolism

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