The lesion site in malignant psoas syndrome influences the cancer pain intensity.

BACKGROUND: Malignant psoas syndrome (MPS) is characterized by pain and hip flexion fixation due to tumor infiltration of the iliopsoas muscle. However, the dose of opioid required to control pain varies markedly among MPS patients. As the ability to predict whether an MPS patient will need a higher opioid dose in the early period of pain control is clinically meaningful, we retrospectively evaluated the relationship between lesion site in MPS and the opioid dose required for pain control. METHODS: Fourteen patients received opioid control of cancer pain due to MPS between January 2014 and December 2018. Two patients with paraplegia who died during pain control were excluded from this study. The remaining 12 patients were divided into group of muscle attachment (group MA) (n=6), with the lesion in the iliopsoas MA to the spine, and group of muscle belly (group MB) (n=6), with the lesion in the iliopsoas MB. We compared opioid doses for pain control between groups. RESULTS: No significant differences in background characteristics were seen between groups. Opioid dose (in oral morphine equivalents) was significantly higher in group MB (1,374.3±504.5 mg/day) than in group MA (92±67.9 mg/day; P=0.0007). CONCLUSIONS: MPS patients with the lesion in the MB appear to need a higher opioid dose for pain control than patients with the lesion in the MA.