Intrathecal morphine use for CNMP treatment has increased considerably recently, having an important place in the management of such complex cases. Nevertheless, a general consensus on clinical indication for selected patients is not followed by its clinical application indeed [11
Constant flow infusion systems fulfill requirements of continued drug delivery in CSF and provide a relatively high concentration of the drug close to opioid receptors in spinal cord [6
]. This method is more likely to promote analgesia with doses significantly lower than oral and intravenous administration.
Only 3 products have been officially approved for long-term intrathecal administration: morphine, baclofen, and ziconotide. The efficacy of intrathecal ziconotide for the management of patients with severe chronic refractory non-cancer pain was illustrated in 3 placebo-controlled trials, showing a benefit over a short follow-up period for patients with pain due to cancer or AIDS. The efficacy of intrathecal opioid administration for the management of chronic noncancerous pain is mainly derived from prospective and retrospective non-controlled trials [12
Our study analyses the benefits of intraspinal morphine in patients with CNMP of different etiologies. Although retrospective and with a small sample, the group of patients typifies the most frequent etiologies for intraspinal opioid therapy, 45% of these with FBSS.
Patients with psychiatric associated disease were excluded, as is extensively recommended in literature. In congruence with this recommendation and with recognized indications, we believe that the rigorous selection of patients is the key for the success of intra-spinal opioid therapy.
A recent consensus on intrathecal drug delivery (IDD) [13
] highlights that analgesic response to IDD has been seen in patients with neuropathic, visceral, deafferentation, and mixed pain. Panelists noted that patients with some conditions – such as headache, fibromyalgia, atypical facial pain, noncancer head–neck pain, and borderline personality disorder – have not had good outcomes. Although patient selection varies widely among practitioners, the goal is to identify the patients whose pain states are likely to be relieved by intrathecal medication.
Literature diverges on a strict method in trialing patients for intrathecal opioid use, some authors [14
] using both intrathecal and epidural morphine. But all agree that a general improvement of at least 50% in pain condition after opioid test favors a definitive device implant.
Most of studies concerning intrathecal opioid treatment consider the use of an electronic device, what indeed appears to control pain in a better way, easily meeting pain demands by changing infusion program [15
]. However, in our experience using a gas driven constant flow infusion pump, we also could obtain optimal doses during the day and manage adverse effects without difficult.
In the two largest studies published by Winkelmüller and Winkelmüller [16
] with 120 patients and that by Paice et al. [17
] with 429 patients, two-thirds of patients showed a good to an excellent response after morphine pump implant. In our series, we observed that 91% of patients presented a general improve in pain scores after one month of the implant, showing a decrease on VAS around 66%, though did not achieved a permanent decrease on VAS in the last follow-up (41%).
Our rate of improvement is consistent with other reports in their last patient observation: 57.5% (16 patients, 49-month) [18
], 36% (30 patients, 24-month) [14
], 62% (132 patients, 12-month) [19
]. Like we did, these studies also relate a decrease in the grade of improvement in a final following, but any specific clinical or individual condition was associated to this outcome.
Some aspects should be considered when explaining the partial and non-permanent decrease of VAS scores with intrathecal morphine for CNMP, not only in this series. In general, these patients have experienced a pain condition difficult to manage, generally they`ve had poor access to rehabilitation therapies and finally may present psychological issues as a consequence of dealing with pain for a long time [18
]. In this aspect, intrathecal morphine pump implant or other therapeutic procedure opposes against only one aspect of the disease, giving rise to unsatisfying results because other important factors are not being treated.
Despite the absence of a control group and the concomitant use of oral analgesics in the course of intrathecal morphine therapy, the evident differences on VAS after pump implant show the benefits this therapy could bring for our patients. Although this study did not explore important outcomes like return to work and quality of life indices, when questioned about the importance of intrathecal morphine in the roll of pain therapy, patients who benefited from it reported a positive change in daily life activities after implant.
At first, the percentage of decrease on VAS in our study may not mean a strong improve evoking criticisms in proposing patients a chronic intra-spinal opioid therapy. However, ratifying the comments of Slavin [18
], these patients had already failed all other available analgesic interventions, such that intrathecal opioids for them may be the last resort, even though half of patients exhibit a good response.
We added bupivacaine to morphine in 45% of patients, mainly in order to diminish morphine adverse effects without loss of analgesia. Anderson and Burchiel [14
] did the same in 20% of cases.
The practice of associating other drugs to opioids in an intra-spinal deliver is not new. Krames and Larming [20
] studied the combination of bupivacaine and morphine in 20 of 26 patients with CNMP verifying good analgesia and reduction of adverse effects due to morphine. Posteriorly, Rainov, et al. [21
] also viewed the same benefit when morphine was combined with bupivacaine, midazolam and clonidine in different settings, while studying 10 patients with pain of spinal origin.
Two patients (18%, both female ones) had inadequate analgesia with intrathecal morphine, even after managing oral medications. We believe that in these cases, in which pump was also been withdrawn, indications for surgery should be revisited (generalized pain and coccidinya). Rates of explanted patients varied among authors, 6.66% [14
], 12.5% [18
], but the main reasons generally were the same (inadequate analgesia and intolerably opioid side effects).
This outcome shows that a specific population of implanted patients will not experience the benefits of intrathecal opioids, despite well managed. Randomized and controlled studies are needed to show who such individuals are.
The low infection rate in our case series, the absence of drug overdose and the effective control of pain reaffirm the safety and reliability of infusion systems for intra-spinal drug administration.
Here we showed the possibility of using an infusion system different from electronic devices and reproduce equivalent good results, with security and with a low rate of complications. This reinforces the importance of gas driven pumps as another option to intra-spinal therapy in CNMP patient’s population, known for having a long operating life, maximum drug capacity in a minimum pump size with no battery to ever be replaced.