Complications involving spinal cord stimulation and implantable pulse generators

Scenario

A 42-year-old man came into the clinic as a referral to reposition or at least evaluate his spinal cord stimulator system. He had a long history of several revisions which he described at some length after a series of probing questions trying to unravel the precise history of what was done, when, and why. Some of these records were sent from other providers, and although available, they did not necessarily clarify all the details of what had been done previously. Initially, he said “a single wire” was placed at the time of the trial, or just afterward, which he could not recall now. This never helped him at all for his back pain, and he remembers he felt something like a TENS unit in his leg but it was n’t in the right area of his pain. That doctor, he said, told him that the lead had moved and “pulled out” or something and that he replaced it with two wires he thinks, but it required two different procedures somehow, and he was n’t sure what was done during each of them. This revision helped his pain, eventually, for a couple years, but then one wire broke, he thinks he was told, and he did n’t have any stimulation really covering the area where his pain has remained, despite several times seeing the company representative and having reprogramming done. More recently, perhaps in the last 6 months, his pain physician retired and his primary care physician (PCP) would not prescribe the same medications for his pain that he was previously obtaining from his pain doctor. He wanted to see if anything could be done with the stimulator or whether he should just have it removed.

• Variation : The patient was referred instead for spinal cord stimulation “ not working” -- Often patients come into clinic with spinal cord stimulation (SCS) problems and say “It’s not working”. This is a catch-all phrase that needs a degree of probing to determine the exact nature of what is meant. This is critical for the simple reason that many patients have been informed, by other providers or friends and family, or have come to some conclusion on their own about what the problem is. So, they typically have some set of presumptions which needs to be worked through, and unless there is a fairly systematic thought process, the evaluation can become derailed quickly. In general, the algorithm involves determining a couple of important distinctions:

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    Does the patient feel any stimulation at all? (assuming it is paresthesia-based)

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    If not, it is important to determine whether they have ever felt stimulation, given the growing use of “nonparesthesia”-based systems, whether HF10 or subthreshold.

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    If they feel stimulation, is it where they have pain?

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    If it’s not felt in the right areas, then reprogramming is needed.

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    If it’s felt in the right areas but does n’t help their pain, little can be done except (if available) reprogramming with other frequencies and pulse widths, but this is typically less successful although not impossible.

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    If it’s felt in the right areas but the feeling is annoying or adds to their pain, then reprogramming can be helpful, but this may be a sign that the therapy now is not going to be helpful for the patient even if it had been in the past.

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    If no stimulation is felt, does the device actually turn “on”? This type of evaluation can often be accomplished relatively quickly by the company representative at the clinic visit. They can also then determine expected battery life remaining, whether the device seems to have communication problems, and whether recharging (if it’s rechargeable) is working correctly. They can also check impedances within the system and determine usually if there is a lead break somewhere or a complete disconnection.

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    Sometimes, X-rays are helpful if a possible break or intermittent break is suspected, although it can be difficult to be sure if there is a break in a wire by X-ray alone, and often the end result of the evaluation is that the system has to be surgically explored and evaluated intraoperatively by directly testing the lead(s) alone, disconnected from the implantable pulse generator (IPG), no matter what is thought to be seen on an X-ray. In most of these cases, but not all, the lead and IPG need to be replaced – but it is worth verifying each of them before assuming that is the case.

• Variation : The patient is referred instead for a “new pain” -- If the patient begins by explaining that they think their pain is different than it had been or they have the same pains they always had but with additional new pain in a different location, it is important to distinguish whether the new pain is caused by the electrical aspects of the SCS itself or a new underlying anatomical development or potentially a mechanical change related to the stimulator itself (i.e., the lead, scar, or the IPG). A simple way to do this (which the patient may have tried but more often has not) is to turn the system “off” for an extended period of time and see whether the pain still occurs. This may seem obvious, but there is a certain amount of “washout” period necessary and the patient may have tried it for too short a time (usually several days are need to be sure) or the patient has been reluctant to turn the device off because it helps them with their underlying pain too much and they do not want to feel that pain back again. Many times, the patient has not actually thought of turning the device “off” at all but has also frequently come to the potentially erroneous conclusion that the device is the cause of their new pain. In any case, it is important to try to have this assessment made as a first step most of the time. Other components of the algorithm are as follows:

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    If they still feel the same pain when the device is turned “off” and it is a pain possibly related to the spine somehow, then imaging may be needed to determine its cause (e.g., it seems to be a new radiculopathy). If the device is magnetic resonance imaging (MRI) compatible, an MRI can be obtained; if not, a CT myelogram can be obtained.

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    If the new pain is more relatable to areas near the IPG itself, or the thoracic or cervical incisions, then it depends on how severe this pain is and the nature of it. Pain caused or exacerbated by palpation near these regions is likely due to pressure from the device components under the nerve endings within the dermis – this often occurs as scar matures and contracts and after notable weight loss. Lidoderm patches can be tried initially and are often helpful, but in many cases, they are not adequate, and revising the site in the operating room (OR), in some cases moving the IPG (for example) to an entirely different location, needs to be considered. Such circumstances are not uncommon, although certainly not in the majority of cases.