To the Editor:—
Although intrathecal opioid infusions did bring an innovative approach to the treatment of chronic severe, unrelenting pain, the articles by Yaksh et al. 1and Gradert et al. 2revealed that, as with tachyphylaxis, it is only a matter of time and dosage until granuloma-like formations develop at the tip of the catheter. As with previously reported cases of complications with this system, syrinx formation3and lymphedema in patients with previous venous stasis,4the risks of this therapeutic modality are now being recognized, in spite of reports5,6that have claimed little morbidity in the past.
Both studies1,2used the trade preparation Infumorph (Elkins-Sinn, Inc., Cherry Hill, NJ) (25 mg/ml) in their studies, but as Yaksh et al. 1noted, higher concentrations of morphine “prepared” by local pharmacies will be more prone to produce granulomas and tachyphylaxis. They also showed that in some cases, inflammatory masses begin to form within 2–4 months after implantation, but there was little mention of the clinical signs and symptoms related to this complication, which include (1) increased resistance to aspirate cerebral spinal fluid through the catheter port; (2) decreased compliance during injection of 0.9% NaCl; (3) unexplained failure to relieve pain; and (4) disparity between the volume of expected morphine as calculated by the computer versus the volume of morphine actually found in the reservoir before refilling.
It is expected that these volumes be recorded every time the pump is refilled; however, not everyone is doing it. It is assumed that as the catheter tip gradually becomes occluded by the granuloma, less of the morphine is infused into the cerebrospinal fluid. The patient’s pain is not relieved, so the tendency is to increase the dosage, which in turn will favor growth of the granuloma.
Either magnetic resonance imaging (with contrast and with the pump shut off) is to be obtained or a “pump myelogram” may be attempted with 50% diluted contrast media after aspirating the catheter contents. The diagnosis of granuloma should be confirmed by either of these imaging tests.
Among the references listed in both articles, there were more than 20 cases reported; however, this number is in all probability just “the tip of the iceberg” because many cases have gone unreported or unrecognized. Manufacturers are obligated to follow each case and produce reliable reports of the pumps’ outcome for all parties involved. Perhaps now they can come forward with their data because it is essential to determine the precise incidence of this complication.
Sunshine Medical Center, Chipley, Florida. firstname.lastname@example.org