A cross-sectional, comparative, syndromic description of oncological mixed pain in Medical Oncology units in Spain

Objective: The reason cancer pain remains prevalent and hard to classify may be partially explained by the failure to identify neuropathic mechanisms. The objective of this research was to identify the syndromes of cancer pain that may be particularly hard to manage due to their mixed pathophysiology. Design: A series of 384 patients who had cancer of any type, at any stage, and suffered from chronic pain (symptom onset > 3 months) were assessed during a routine return visit in Spain. Medical oncologists indicated the presence and pathophysiology of 33 predefined pain syndromes on a per-patient basis. This information was then measured against clinical, psychosocial, and health care-related data to determine which syndromes pose particular challenges. Results: The mean (standard deviation) age of patients was 61.6 (12.6) years, 49.7% were women. Most (82%) had advanced metastatic disease, 68.7% were on second-line or palliative therapies. The worst syndrome was nociceptive, pure neuropathic, and mixed in 34.6, 26.9, and 38.6% of patients, respectively. Any syndrome could be of mixed pathophysiology. Only 10 syndromes were common (≥ 5% of patients). Syndromes related to malignant bone pain and involvement of chest wall structures were the most frequent. Certain syndromes (including tumor-related bone pain, chemotherapy-induced peripheral neuropathies, paraneoplastic pain syndromes, and malignant neuralgias or injury to cranial nerves) can be particularly challenging when they have a mixed pathophysiology, because the neuropathic component is rarely or unevenly considered. Conclusions: Virtually all cancer pain syndromes can present mixed pathophysiology. Certain syndromes can include neuropathic components that are frequently overlooked.