Summary

DOI: 10.1373/Clinchem.2007.101428

A 15-year-old white girl presented with neck tenderness. On examination, a nodule was palpated in the right thyroid lobe. The neck was supple without abnormal lymphadenopathy. Eye findings related to Graves orbitopathy were absent. Weight, height, and blood pressure were unremarkable, but the heart rate was high at 104–114 bpm. The patient had a history of attention deficit hyperactivity disorder and was taking atomoxetine and fluoxetine. There was no history of childhood neck irradiation or family history of thyroid cancer. Several maternal relatives have acquired thyroid dysfunction.



Student Discussion

Student Discussion Document (PDF)

George van der Watt,1* David Haarburger,1 and Peter Berman1

1Division of Chemical Pathology, National Health Laboratory Service, Groote Schuur and Red Cross Children’s Hospitals, University of Cape Town, Observatory, South Africa.
*Address correspondence to this author at: Division of Chemical Pathology, National Health Laboratory Service, Groote Schuur and Red Cross Children’s Hospitals, University of Cape Town, Observatory, South Africa, 7925. Fax +27216585225; e-mail george.vanderwatt@chempath.uct.ac.za.

Case Description

A 15-year-old white girl presented with neck tenderness. On examination, a nodule was palpated in the right thyroid lobe. The neck was supple without abnormal lymphadenopathy. Eye findings related to Graves’ orbitopathy were absent. Weight, height, and blood pressure were unremarkable, but the heart rate was high at 104–114 bpm. The patient had a history of attention deficit hyperactivity disorder (ADHD) and was taking atomoxetine and fluoxetine. There was no history of childhood neck irradiation or family history of thyroid cancer. Several maternal relatives have acquired thyroid dysfunction.

Sonography showed a 2-cm nodule in the right thyroid lobe. Fine-needle aspiration showed benign cytology, but the family requested right thyroid lobectomy for persistent neck tenderness. Preoperative laboratory data revealed a total thyroxine (T4)3 concentration of 170 nmol/L [reference interval (RI) 67–138 nmol/L] (13.2 μg/dL, RI 5.2–10.7), total triiodothyronine (T3) concentration of 3.2 nmol/L (RI 1.3–2.4 nmol/L) (206 ng/dL, RI 86–153), a thyroid-stimulating hormone (TSH) concentration of 0.5 mIU/L (RI 0.3–5.0 mIU/L), and a thyroid hormone binding ratio (1/T-uptake) of 1.72 (RI 0.77–1.16) (Table 1). Analyses were conducted by chemiluminescent immunoassay on the Roche Elecsys 2010 platform. Free T3 and free T4 indices as calculated by the clinicians were 5.5 nmol/L (RI 1.3–2.4 nmol/L) and 292 nmol/L (RI 67–138 nmol/L), respectively, and, in the context of the patient’s normal TSH concentration, suggested the possibility of inappropriate TSH secretion due to resistance to thyroid hormone or a TSH-secreting pituitary adenoma. Analyses for serum free T4 measured by direct dialysis and RIA were conducted at Mayo Medical Laboratories and revealed a normal free T4 of 16.8 pmol/L (RI 10.3–25.8 pmol/L) (1.3 ng/dL, RI 1–2 ng/dL). Although certain of the patient’s features, including her tachycardia (1, 2), were consistent with the syndrome of inappropriate TSH secretion, this syndrome is extremely rare and the recommended standard of care is to repeat thyroid function tests after ≥1 week (2) to exclude the effects of nonthyroidal illness and to assess the possibility of laboratory artifact (3). Accordingly, the patient’s scheduled surgery was postponed to accurately assess her thyroid function status.

Questions to Consider

  • What are the possible reasons for discrepancies between thyroid function testing and clinical picture?
  • What are the appropriate next steps to resolve the discrepancy between clinical picture and laboratory results?
  • What would the clinical picture be if the patient had resistance to thyroid hormone? A pituitary adenoma?

Final Publication and Comments

The final published version with discussion and comments from the experts appears in the July 2008 issue of Clinical Chemistry, approximately 3-4 weeks after the Student Discussion is posted.

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DOI: 10.1373/Clinchem.2007.101428
Copyright © 2008 American Association for Clinical Chemistry