Ease the pain: lidocaine infusion for fibromyalgia

Fibromyalgia is a notoriously tricky condition to manage. A central nervous system disorder characterised by widespread pain and fatigue, its symptoms are extensive and somewhat mysterious. With the exact causes unknown, diagnosis can be difficult and treatment more perplexing still.

Unlike, say, post-operative soreness, it is not simply a matter of administering painkillers and waiting for the aches to ebb away. Rather, it's about tackling the disorder on the individual's own terms. While all experience pain of varying intensities, they may also contend with insomnia, headaches, irritable bowel syndrome and depression.

Although it is estimated that 5% of the world's population are sufferers (with women affected more frequently than men), the condition has not long been on clinicians' radars. Indeed, it was only formally recognised in 1990, when the American College of Rheumatology set out its diagnostic criteria. Back then, the checklist included pain in all four quadrants of the body, including at least 11 of 18 designated pressure points.

While this was revised in 2010 to take into account other cognitive and somatic issues, the disorder still isn't widely understood. After all, there are no blood tests or X-rays that can reliably show up fibromyalgia; no specific abnormalities that come to light on a routine scan. Nor can any given treatment be considered a magic bullet.

"Fibromyalgia is a difficult disease in terms of pain," says Dr Billy Huh, a specialist in the field. "There are FDA-approved medications, but some patients respond more and some less. For those with no response, there are no good options."

Huh is well placed to comment, having worked within pain medicine for nearly 20 years. He has published dozens of papers and book chapters, and sits on numerous committees. At present, his role stands as professor and medical director of the department of pain medicine at the University of Texas MD Anderson Cancer Center and adjunct professor of the department of anaesthesiology at Duke University Medical Center.

Of all the conditions he researches, fibromyalgia is one of the most problematic. "It is a combination of so many things," Huh says. "Because it's multifactorial, it's difficult to work to target. A lot of patients need to have a multidisciplinary, multimodal therapy just to get some benefit."

Treatment and remedies

Typical remedies range from the pharmaceutical to the psychological, with antidepressants, anticonvulsants, pain relievers and sleep aids having been shown to help. Increasingly, the condition is seen as the province of neurologists as much as rheumatologists; today's medications are largely designed to regulate the body's neurotransmitters. Lifestyle changes are also recommended.

Unfortunately, certain patients remain unresponsive to conventional therapies. It was for this reason that Huh conducted his latest study, which was presented at the American Society of Anesthesiologists' annual meeting in October 2013. The study concerned an unusual medication: intravenous lidocaine infusion, and asked how efficacious this might be where nothing else has worked.

"With conventional medication you take a pill, but lidocaine infusions are taken intravenously in the clinic," explains Huh. "The patients received anything from 4-5mg/kg over a one-hour period under strict monitoring. On average they received a 10% reduction in pain for about three weeks."

In total, the study involved 55 patients, with statistics collected for sex, race and body weight. Their pain levels were assessed via several questionnaires, before and after the lidocaine infusion. Also measured were the duration of pain and the duration of pain relief.

Before the infusion, subjects registered an average of 83.18 on the brief pain inventory scale, which then dipped to 73.68. Similarly, their average pain interference score (a measure of how much pain impeded their everyday functioning) dropped from 7.73 to 6.88. The infusion was not a cure by any stretch, but it did make a real difference.

This study provides further insight into a contentious area of medicine. According to a 2010 meta-analysis entitled 'Intravenous lidocaine for chronic pain: a systematic review', "IV lidocaine is efficacious for very temporary relief of chronic pain", but "there is a dearth of studies on the benefit of IV lidocaine beyond 24 hours post-treatment". Huh's results suggest that, in the case of fibromyalgia patients, effects can typically be felt for some weeks.

Further findings

The study also brought to light a certain discrepancy between the subjects. While lidocaine worked well for many patients, it showed limited efficacy for smokers and African Americans. In fact, the smokers' average brief pain inventory score after lidocaine was as high as 89.98, skewing the average for the rest.

Huh believes that, in the case of African American patients, the poor results can be attributed to a particular genetic makeup.

"Certain drugs work for African Americans and some work for Caucasians," he says. "There is a lot of genetic variability in the response to medication."

With smokers, the reason is more likely due to vascular damage impairing blood circulation. While lidocaine is normally used as a local anaesthetic, here it is administered intravenously. This means its function relies upon healthy blood flow.

"Fibromyalgia sufferers have pain almost everywhere - there is no target area we can inject," says Huh. "The lidocaine is a numbing medicine, so it will be circulated through the nerve fibres, blocking the sodium channels there. Chronic smokers have poor blood flow, so the circulation of lidocaine to the target nerve is diminished."

Study challenges

Further studies will undoubtedly be of use to clarify these areas and others. Huh's study was a retrospective review, meaning medical records were analysed after the treatments took place. This gives it certain limitations not associated with prospective studies, a lack of randomisation being one. Retrospective studies are more prone to error than their prospective equivalents, and rank lower on the hierarchy of evidence.

Perhaps more problematically, the study lacked any kind of control group. A trial of this kind should involve another set of patients receiving a saline solution. Unfortunately, this would place one in murky ethical territory, especially bearing in mind the realities of the IV procedure.

With an hour required to administer the drug, and another hour to monitor the patient afterwards, infusion is a time-consuming and labour-intensive process. It's a big ask for patient and clinician alike. And while giving subjects a dud sugar pill is one thing, hooking them up to a dud saline drip is quite another.

"With chronic pain patients like this, it's challenging because it's unethical to give a placebo to patients," says Huh. "It's difficult to get approval to give nothing to the patients who are suffering."

Unfortunately, Huh believes that the practical challenges of lidocaine infusion may stand in the way of its widespread adoption. Although it helped many of his patients, it is unlikely to revolutionise the therapeutic picture for other fibromyalgia sufferers. Given its inconvenience, its expense and the possible side effects, the benefits may not justify the costs.

"It's not a cost-effective way to deliver care," says Huh. "Because it takes such a long time, it's only in academic centres like ours that we can afford to do this. It has to be given in the clinic with blood pressure and heart rate monitored, so if something happens, like seizures or arrhythmia, we are ready to intervene. I don't know how widely it can be implemented."

For the time being, there is no easy way of helping out these sufferers, and the condition continues to diminish their quality of life. But with research underway into all aspects of fibromyalgia, it is likely that treatments will continue to improve as the aetiology is more understood.

As for Huh's original patients, IV lidocaine infusions have thrown them a lifeline. "A lot of them come back every month to get a lidocaine infusion, because they find it to be more efficacious than anything else," he says.