The description of neuropathic pain predicts response to Botox
The goal of personalized medicine will be achieved through the exponential growth of computing power. Epigenetics, pharmacogenomics, and machine learning are some of the approaches that are being driven by our ability to process massive amounts of data. Unfortunately, it may take another decade or two before we can offer our patients truly personalized medicine.
Until then, we still have to rely on clinical skills. In a study just published in the journal Pain, D. Bouhassira and his colleagues were able to predict the response of neuropathic pain to Botox injections. The prediction was based on a specific combination of symptoms and signs. They used the Neuropathic Pain Symptom Inventory (NPSI) in 628 patients to identify three distinct clusters of patients. The first group had a more severe pinpointed pain, the second one had more evoked pain, and the third had a higher score for deep pain.
The study included adult patients who had experienced pain for at least three months with a mean pain intensity three or greater on a 0 to 10 numerical rating scale. In more than 85% of the patients, neuropathic pain was due to a traumatic or surgical nerve injury. In the rest, it was due to postherpetic neuralgia (shingles).
The researchers used these three groupings to predicting treatment response through the analysis of their two previous controlled trials of Botox. They found significant effects of Botox compared to placebo in clusters 2 and 3, but not in cluster 1. They also developed and performed a preliminary validation of a web-based version of the NPSI and algorithm for the stratification of patients in both research and daily practice.
Botox is not yet approved by the FDA for the treatment of neuropathic pain. This means that insurance companies are unlikely to pay for it. Besides the pain of shingles, neuropathy, injured nerves (I’ve treated two patients with post-amputation pain), we use Botox “off label” to treat trigeminal neuralgia, cluster headaches, hemicrania continua, numular headaches, and other painful conditions. In one of my patients, even headache due to a large but benign brain tumor responded to Botox.
In treating migraine headaches with Botox, there were several attempts to find clinical predictors of response. More recent onset of chronic migraine and fewer days with migraine have been identified as predictors of a better response. . There have been also suggestions that eye pain was a good predictor of response to Botox. Patients with”exploding” (pressure from inside-out) headache may be less responsive than those with “imploding” (pressure from outside-in, or constricting pain) headache.
When studied in large groups, these features might have some predictive value. But it is not anywhere close to 100% or even 70%. Therefore, when dealing with an individual patient we would try Botox in patients with chronic migraines regardless of the presence or the absence of any of these symptoms.
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