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

Summary 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 ( NET s) 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 NET s may provide insights into the relationship between serotonin and BMD . Methods One‐year audit of consecutive patients with NET s 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 NET s, 19 did not participate or were excluded. Of 46 subjects evaluated (48·9% males, 63·8 ± 10·5 years, BMI 26·6 ± 4·4 kg/m 2 ) with 32 gastrointestinal, 9 pancreatic, 3 pulmonary and 2 ovarian NET s, 72·3% had the carcinoid syndrome. Median interval from diagnosis was 4·0 years ( IQR 2·0–6·0); 41·3% had osteoporosis and 32·6% 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 −0·41, P  = 0·004; −0·44, P  = 0·002, 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 NET s 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 NET s should be subject to targeted osteoporosis prevention.