Extremely Low Numbers of Cases
A topical CME article (1) should provide guidance that is evidence based. This was often not the case in the article under discussion. An example: The authors say that the serum calcitonin concentration should be measured in every patient with euthyroid nodular goiter, in order to ensure that medullary thyroid carcinoma (MTC) is not missed. Medullary thyroid cancers constitute 7% of all thyroid cancers.
In Germany, 5350 cases of thyroid cancer are diagnosed every year (Robert Koch–Institute, 2010); this translates into 400 cases of MTC. 780 patients die from thyroid cancer, among them 250 from MTC. These are extremely low case numbers compared with other preventable causes of death.
400 cases of MTC have to be seen against 10 million people with nodular goiter (20% of the adult population) who should have their calcitonin measured. This corresponds to 1 patient with MTC in every 25 000 cases of nodular goiter. When conducting investigations with such poor ratios of examined patients to actually affected patients, the result—in contrast to targeted diagnostic evaluation—will always be more false-positive findings than true-positive ones.
This means: Herrmann et al (2) found a prevalence of MTC in their German studies of 0.2%; international rates are comparable (3). When a specificity of calcitonin testing of 95% and a sensitivity of 100% is assumed, the positive predictive value is 4%. This means that on the basis of a positive calcitonin test—even if a pentagastrin-stimulated test is used additionally—25 patients would have to to be operated in order to maybe help one of them. An operation is always necessary since CT and fine needle aspiration biopsy are less exact than the calcitonin test and therefore cannot be used to safely rule out cancer.
All this is not discussed in the article, but—in contrast to international perspectives (3, 4)—the test is recommended as a routine. One might assume that it is up to anybody to make a “recommendation.” However, in the context of a CME article, a recommendation becomes binding in a way that should not be underestimated—and can be risky in this setting.
Prof. Dr. med. Heinz-Harald Abholz
Institut für Allgemeinmedizin, Heinrich-Heine-Universität-Düsseldorf
Elizabeth Bandeira-Echtler, Cochrane Group für Metabolic
and Endocrine Disorders, Heinrich Heine-Universität-Düsseldorf
Prof. Dr. Johannes Köbberling, Wuppertal
Conflict of interest statement
The authors declare that no conflict of interest exists.
|1.||Führer D, Bockisch A, Schmid KW: Euthyroid goiter with and without nodules—diagnosis and treatment. Dtsch Arztebl Int 2012; 109(29–30): 506–16. VOLLTEXT|
|2.||AACE/AME/ETA: Thyroid Nodule Guidelines, Endocr Pract 2010; 16(Suppl 1). MEDLINE|
|3.||Daniels GH: Screening for medulalary thyroid carcinoma with serum calcitonin measurments in patients with thyroid nodules in the US and Canada. Thyroid 2011; 21: 1199–207. MEDLINE|
|4.||Herrmann BL, Schmidt KW, Goerges R, et al.: Calcitonin screening and pentagastrin testing: predictive value for the diagnosis of medullary carcinoma in nodular thyroid disease. Eur J Endoc 2010; 162: 1141–5. MEDLINE|