Intrathecal catheter tip inflammatory mass: a failure of clonidine to protect.

INTRATHECAL drug infusions are being used more frequently to treat spasticity and chronic pain. More than 95,000 intrathecal drug administration devices have been implanted in the United States since their development in the 1980s. When opioids are part of the intrathecal infusion solution, catheter tip granulomas are emerging as an important potential complication. More than 90 cases of catheter tip granuloma have been reported since 1992. Complication reporting is currently on a voluntary basis, and this number is likely understated. The granuloma is typically a collection of acute and chronic inflammatory cells derived from the arachnoid layer. This reactive tissue does not seem to directly involve the neural parenchyma but has the potential to compress the spinal cord and produce permanent neurologic deficits, including paralysis, sensory loss, and impairment of bowel and bladder function. In sheep and dog studies, intrathecal morphine infusions reliably produce catheter tip granulomas. Within the human population, their development is less predictable. Morphine concentration and total daily dosage seem to influence the development of granulomas. The incidence increases with the duration of intrathecal therapy and has been reported as 0.4% after 2 yr of therapy and 1.16% after 6 yr of therapy. The incidence of asymptomatic lesions may be much higher. In a cohort of seven patients, identification of a single symptomatic lesion led to imaging and identification of two additional asymptomatic lesions. In a small canine study, combination therapy with morphine and clonidine was found to prevent granuloma development when the clonidine infusion was greater than 250 g/day. On this basis, some physicians who manage patients with intrathecal analgesic infusion systems recommend the routine use of clonidine as an adjunct with opioid to inhibit granuloma formation (personal observation, Kenneth Follett, M.D., Ph.D., Professor, Department of Neurosurgery, University of Iowa, Iowa City, Iowa, verbal communication, June 2004). We describe a case in which continuous infusion of intrathecal clonidine did not prevent granuloma formation after subsequent addition of morphine to the intrathecal infusate. This observation suggests that clonidine may not have the same granuloma-inhibiting effect in humans that has been described in animal models.