[A case of malignant psoas syndrome diagnosed while treating sciatica].

While attempting to treat a 71-year-old male patient who had been diagnosed with sciatica from spinal canal stenosis, we discovered his prior cancer metastasizing to the psoas. We initially administered epidural block to him after confirming his prior rectal cancer had not metastasized to lumbar vertebral bones, but the block did not satisfactorily alleviate his pain, and he had difficulty stretching his lower limbs. CT scan to re-examine the cause revealed a metastasized cancer in the psoas. From this experience, we believe malignant psoas syndrome should be considered in addition to metastasis to lumbar vertebral bones, when evaluating lower back to lower limb pain in patients with previous cancer history.