Analysis of breakthrough pain in 50 patients treated with intrathecal morphine infusion therapy - Development of tolerance or infusion system malfunction

Fifty patients with intractable benign pain were treated with intrathecal morphine (IT-MS) infusion therapy. Median follow-up was 39 months (range 5-70). Breakthrough pain was reported in 35 (90%) patients in 75 outpatient clinic events. A diagnostic algorithm was developed to evaluate and efficiently treat these patients. A programmed bolus (50% of daily dose) identified that 50 (67%) breakthrough events where due to partial tolerance to the IT-MS. Radiographic survey of the catheters identified malfunctions in 11 patients. Attempts to withdraw CSF from the side-port demonstrated obstruction in 7 due to kinking not seen on X-rays. Side-port myelography demonstrated scarring that obstructed the flow of morphine to the spinal cord in 2 patients. Benefits were regained after all surgical catheter corrections. In total, partial tolerance was seen in 23 patients (46%) during 50 (67%) breakthrough events, 15 patients (30%)-required 22 catheter revisions during 27% of breakthrough events and 2 patients had progressive disease. True tolerance was encountered in only 5 patients (10%) during 5 (7%) breakthrough pain events.