Are serotonin metabolite levels related to bone mineral density in patients with neuroendocrine tumours?

Background Bone mineral density (BMD) is influenced by multiple factors. Recent studies have highlighted a possible relationship between serotonin and BMD. Patients with neuroendocrine tumours (NETs) frequently have elevated urinary 5-hydroxy-indoleacetic acid (5-HIAA) levels, a serotonin metabolite. Evaluation of the relationship between 5-HIAA and BMD in patients with NETs may provide insights into the relationship between serotonin and BMD. Methods One-year audit of consecutive patients with NETs within two institutions. Relationships between urinary 5-HIAA and dual X-ray absorptiometry (DEXA)-scan-measured BMD were investigated by group comparisons, correlation and regression. Results Of 65 patients with NETs, 19 did not participate or were excluded. Of 46 subjects evaluated (489% males, 638 105years, BMI 266 +/- 44kg/m(2)) with 32 gastrointestinal, 9 pancreatic, 3 pulmonary and 2 ovarian NETs, 723% had the carcinoid syndrome. Median interval from diagnosis was 40years (IQR 20-60); 413% had osteoporosis and 326% osteopaenia (WHO definition). The group with a higher urinary 5-HIAA had a lower hip BMD (total T-score and Z-score), confirmed on individual analysis (Spearman's rank correlation -041, P=0004; -044, P=0002, respectively); urinary 5-HIAA was not found to be an independent predictor for BMD on multiple linear regression analysis. Conclusion These data of patients with NETs with higher serotonin metabolites having a lower BMD at the hip in group and individual comparisons, warrants further evaluation. Urinary 5-HIAA measurement alone cannot be used to predict future BMD. A larger cohort with prospective design including fractures as a clinical outcome will aid these data in determining whether patients with NETs should be subject to targeted osteoporosis prevention.