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Not All Intrathecal Catheter Tip MRI Findings Are Inflammatory Masses

Section Editor(s): Saidman, LawrenceCoffey, Robert J. MD; Allen, Jeffrey W. PhD

doi: 10.1213/01.ane.0000260557.76884.72
Letters to the Editor: Letters & Announcements

Medtronic Inc.; Minneapolis, MN;

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To the Editor:

We are grateful to Murphy et al. (1) for reporting their case of a patient who developed a suspected catheter tip obstruction and subsequent loss of therapeutic effects after having received intrathecal baclofen. We compared their report with the collective clinical and preclinical experience regarding inflammatory masses, and offer two observations.

First, our previous laboratory studies, published analyses of medical-device reports, consensus-panel reports, and the information presented in this case lead us to believe that Murphy et al.’s patient most likely did not have a catheter tip inflammatory mass lesion, at least, not the type we have seen in preclinical studies and physician reports. Her symptoms of fluctuating ITB efficacy may have been catheter-related, but we do not see a strong case for those symptoms being related to the MR image in the case report.

Specifically, the irregularity around the catheter tip is not typical of the opioid-induced inflammatory mass lesions reported to arise at the tip of intrathecal drug administering catheters in human patients and animal models. Catheter tip inflammatory masses usually are distinct, globular- or spheroid-shaped lesions best visualized on T1 MR image sequences with gadolinium contrast (2,3) (Fig. 1). Imaging diagnosis based on other criteria can be misleading. For example, precipitated drug can mimic a tumor or inflammatory mass lesion in patients with implanted spinal drug-delivery systems (4). Murphy et al.’s published noncontrast image reveals an ill-defined irregularity that does not appear large enough to occlude all or most of the drug-administration apertures, as these extend circumferentially to 15-mm proximal to the catheter tip. The loss of efficacy most likely was due to catheter problems unrelated to the MRI findings, especially because the second contrast injection confirmed patency. As the catheter was patent, the MRI findings were incidental to the loss of efficacy.

Figure 1

Figure 1

Second, the case report attributes the MRI findings and a clinical complication to intrathecal baclofen but provided no information on drug concentration, pump flow rate, or whether the drug administered to this patient was the approved, preservative-free formulation of Novartis Lioresal Intrathecal® (baclofen injection). Murphy et al. cited our previous work and referred to our statement in 2002 that “No masses were reported in patients who received baclofen as the only intrathecal medication” (5,6). We emphasize that animal studies (7) and hundreds of thousands of patient-years of clinical experience with Novartis Lioresal Intrathecal have not identified a single case of a catheter tip mass lesion.

Preliminary experimental evidence suggests that dural mast cell activation and subsequent release of inflammatory mediators (such as cytokines, and histamine) are responsible for catheter tip inflammatory mass lesions (8,9). To our knowledge, there are no reports of baclofen producing mast cell activation. These findings dovetail with clinical reports of inflammatory mass lesions and direct spinal cord toxicity that appear to have been caused by compounded and/or impure drugs, or the long-term administration of drug formulations not specifically tested and approved for chronic intrathecal use (10–12). We emphasize the importance of limiting intrathecal drug delivery to drugs that are tested and approved for this route of administration.

Robert J. Coffey, MD

Jeffrey W. Allen, PhD

Medtronic Inc.

Minneapolis, MN

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© 2007 International Anesthesia Research Society