Endocrine Abstracts

We report a case of a false positive pentagastrin stimulation test in a patient with a positive family history for medullary thyroid cancer (MTC), but normal histology following total thyroidectomy.

An asymptomatic 50-year-old man was referred urgently with an elevated calcitonin level of 19.9 ng/l (reference range<11.8), taken following the diagnosis of his brother with MTC which had been discovered on a routine private medical examination. There was no family history of multiple endocrine neoplasia. A pentagastrin stimulation test was performed, which demonstrated an elevated calcitonin at baseline (29.8 ng/l), a peak at 1 min (195 ng/l) and a slow return to baseline, consistent with a positive test for underlying MTC.

Further investigations for urinary catecholamines, chromogranin A and B, PTH, calcium thyroid ultrasound and an MRI neck were all normal. Genetic testing was consented for and the results were pending whilst he was under investigation.

The patient proceeded to a total thyroidectomy despite not having the results of genetic testing. The thyroid and cervical lymph node biopsies demonstrated normal histology, with no evidence of C-cell hyperplasia or malignant change. Genetic analysis confirmed carriage of the RET proto-oncogene mutation in the patient’s brother and sister, but our patient did not carry the abnormality. Post-operative repeat calcitonin is awaited.

This case questions of the role of the pentagastrin stimulation test as a diagnostic test for MTC. Our patient had a strong family history of MTC and a raised calcitonin level on screening and was adamant that he wanted to proceed to total thyroidectomy. He does not regret having total thyroidectomy and affirms he would make a similar decision again. A second opinion is awaited on the thyroid histology.