Differentiation between healthy thyroid remnants and tumor tissue after radioiodine therapy in patients with differentiated thyroid carcinoma using in-vitro phosphorus-31 magnetic resonance spectroscopy

Full text: In many tumors, tumor growth and spread is triggered by changes in cell membrane metabolism, which can lead to systemic alterations in levels of phospholipids. The aim of this study was to differentiate between healthy remnants of thyroid tissue and residual/recurrent tumor tissue or metastases in patients with thyroid carcinoma by measurement of plasma levels of various phospholipids. Phospholipid concentrations was measured by in-vitro phosphorus-31-magnetic resonance spectroscopy (31P-MRS) in blood samples from 30 patients with thyroid cancer, who had been rendered hypothyroid in preparation for diagnostic/therapeutic administration of iodine-131. All patients were already thyroidectomized. 131I-whole-body scintigraphy and measurements of thyroglobulin values in a 2-year-follow-up were used to distinguish between patients in remission, patients with only healthy thyroid remnants and patients with cancerous thyroid tissue and/or metastases. Significantly lower blood plasma levels of systemic sphingomyelin (0.33±0.06 vs. 0.46±0.03 (controls) mmol/l; p<0.0001) and phosphatidylcholine (1.3±0.2 vs. 2.1±0.3 (controls) mmol/l; p<0.0001) were found in patients with metastasic thyroid cancer than in patients in remission (controls) and this difference was related to the extent of tumor growth and/or metastasis. In patients with only healthy remnants of thyroid tissue there was a significantly smaller decrease in systemic phospholipids (sphingomyelin: 0.41±0.06; phosphatidylcholine 1.7±0.3 mmol/l; p=-0.007). In-vitro 31P-MRS can be used to differentiate between the presence of tumor tissue, healthy remnants of thyroid tissue not requiring further treatment and remission in patients with thyroid cancer. In future, therefore, plasma 31P-MRS could be developed as an additional diagnostic tool for the follow-up of differentiated thyroid cancer. (author)