Abnormal endocrine tests in chronic pain require investigation and are not the result of opioid analgesia
Z Merza1, N Edwards2, S Walters3, J Newell-Price1 & RJM Ross1
Background: Anecdotally patients with chronic pain on opioid analgesia have functional hypopituitarism, and studies in opioid addicts show suppressed pituitary function. We conducted a prospective observational study to determine the endocrine status of patients with chronic pain on opioid analgesia. Methods: 37 consecutive patients with chronic back pain attending the pain clinic were enrolled. 22 patients (age 45+/-9 years) were on long-term opioid analgesia and 15 (age 53 +/-10 years) were on non-opioid analgesia. Patients underwent basal and dynamic endocrine function testing including: fT4, TSH, FSH, LH, oestradiol, testosterone, SHBG, PRL, ACTH, IGF-1, glucagon and short synacthen test. Patients gave written consent and the study was approved by the local ethics committee. Results were compared between the 2 groups and to the normal ranges. Results: We found no significant difference between the 2 groups in all hormones measured with the majority of patients having normal results. One patient had thyrotoxicosis, two patients in each group had a subnormal GH response to glucagon stimulation, however three of these patients were obese and all patients had a normal IGF-I. One patient in the opioid group had inappropriately low gonadotropins for a post-menopausal woman. Two patients in the opioid and one in the non-opioid group had low testosterone levels, however the free androgen index was normal in 2 and the low total testosterone was related to obesity. The short synacthen test results were suboptimal in three on opioids and one non-opioid patient, but ACTH levels and repeat synacthen tests were normal in all four. Conclusion: Oral opioids in moderate doses, used for the treatment of chronic pain, do not cause functional hypopituitarism. Therefore, abnormal endocrine tests in such patients require investigation and cannot be explained on the basis of their analgesia.