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Nuklearmedizin 2003; 42(06): 240-243
DOI: 10.1055/s-0038-1625734
Original Article
Schattauer GmbH

Iodine excretion during stimulation with rhTSH in differentiated thyroid carcinoma

Iodexkretion während Stimulation mit rhTSH beim differenzierten Schilddrüsenkarzinom
M. Löffler
1   Department of Nuclear Medicine (Head: Prof. Dr. med. O. Schober), University of Münster, Germany
,
M. Weckesser
1   Department of Nuclear Medicine (Head: Prof. Dr. med. O. Schober), University of Münster, Germany
,
C. Franzius
1   Department of Nuclear Medicine (Head: Prof. Dr. med. O. Schober), University of Münster, Germany
,
P. Kies
1   Department of Nuclear Medicine (Head: Prof. Dr. med. O. Schober), University of Münster, Germany
,
O. Schober
1   Department of Nuclear Medicine (Head: Prof. Dr. med. O. Schober), University of Münster, Germany
› Author Affiliations
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Publication History

Received: 06 May 2003

in revised form: 07 August 2003

Publication Date:
10 January 2018 (online)

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Summary

Aim: Elevated iodine intake is a serious problem in the diagnostic and therapeutic application of 131iodine in patients with differentiated thyroid cancer. Therefore, iodine avoidance is necessary 3 months in advance. Additionally, endogenous stimulation requires withdrawal of thyroid hormone substitution for 4 weeks. Exogenous stimulation using recombinant human TSH (rhTSH) enables the continuous substitution of levothyroxine, which contains 65.4% of its molecular weight in iodine. Thus, a substantial source of iodine intake is maintained during exogenous stimulation. Although this amount of stable iodine is comparable to the iodine intake in regions of normal iodine supply, it may reduce the accumulation of radioiodine in thyroid carcinoma tissue. The aim of this study was to assess the iodine excretion depending on different ways of stimulation. Methods: Iodine excretion was measured in 146 patients in the long term follow up after differentiated thyroid carcinoma. Patients were separated into 2 groups, those on hormone withdrawal (G I) and rhTSH-stimulated patients on hormone substitution (G II). Results: Iodine excretion was significantly lower in hypothyroid patients (G I, median 50 μg/l, range: 25-600 μg/l) than in those under levothyroxine medication (G II, median 75 μg/l, 25-600 μg/l, p <0.027). TSH in G I (median 57.0 μU/ml, range: 14.4-183 μU/ml) was significantly lower (p <0.001) than in G II (117 μU/ml, 32.2-281 μU/ml). Conclusion: Iodine excretion was higher in patients under rhTSH-stimulation than after hormone withdrawal. This may indicate an increased iodine pool in rhTSH-stimulated patients (deiodination of levothyroxine), thus limiting the sensitivity of radioio-dine scanning to the level of endogenous stimulation despite significantly higher TSH levels during rhTSH-stimulation.

Zusammenfassung

Ziel: Eine erhöhte Iodzufuhr ist ein erhebliches Problem in der diagnostischen und therapeutischen Anwendung von 131Iod bei Patienten mit differenziertem Schilddrüsenkarzinom. Deshalb erfolgt eine Iodkarenz über 3 Monate, zudem wird bei der endogenen Stimulation auch die Substitution mit Levothyroxin für 4 Wochen abgesetzt. Die exogene Stimulation mit rekombinantem humanen TSH (rhTSH) wird unter fortgesetzter Substitution mit Levothyroxin durchgeführt. Dieses besteht zu 65% seines Molekulargewichts aus Iod. Dies führt zu einer persistierenden und nicht unerheblichen Iodzufuhr. Obwohl diese Iodmenge die übliche Iodzufuhr in Gebieten mit normaler Iodversorgung nicht überschreitet, kann sie den Radioiod-Uptake in Schilddrüsen-und Schilddrüsenkarzinomzellen beeinträchtigen. Das Ziel dieser Studie war, die Iodexkretion abhängig von der Stimulationsweise zu messen. Methoden: Die Iodexkretion wurde bei 146 Patienten in der langfristigen Tumor-nachsorge bei differenziertem Schilddrüsenkarzinom gemessen. Die Patienten wurden unterteilt in eine Gruppe unter Hormonentzug (G I) und in eine Gruppe unter rhTSH-Stimulation (G II). Ergebnisse: Die endogen stimulierten Patienten wiesen eine signifikant geringere Iodexkretion (Median 50 μg/l, Spannweite 25-600 μg/l) auf als Patienten mit persistierender Hormonsubstitution (75 μg/l, 25-600 μg/l, p <0,027). TSH war in G I (Median: 57,0 μU/ml, Spannweite 14,4-183 μU/ml) signifikant niedriger (p <0,001) als in G II (117 μU/ml, 32,25-281 μU/ml). Schlussfolgerung: Die Iodexkretion ist unter rhTSH-Stimulation höher als nach Hormonentzug. Daraus kann auf einen erhöhten Iodpool in rhTSH-stimulierten Patienten rückgeschlossen werden (De-Iodierung des Levothyroxins). Dies kann die Sensitivität von Iodszintigraphien auf das Niveau limitieren, das auch von endogen stimulierten Patienten erreicht wird, obwohl der TSH-Wert unter rhTSH-Stimulation signifikant höher ist.

Keywords

Iodine excretion - rhTSH - differentiated thyroid carcinoma - thyroid hormone withdrawal - levothyroxine

Schlüsselwörter

Iodexkretion - rhTSH - differenziertes Schilddrüsenkarzinom - Hormonkarenz - Levothyroxin
 

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