Perineural injection of botulinum toxin-A in painful peripheral nerve injury – a case-series: pain relief, safety, sensory profile, and sample size recommendation

<b>Objectives:</b> Subcutaneous injection of botulinum toxin-A (sBONT-A) is a novel treatment for peripheral neuropathic pain. While its analgesic effects are well documented, this treatment often is not comfortable and failed in patients who show signs of sensory loss but rarely allodynia. There are some case reports about perineural BONT-A injection (pBONT-A) which could be an alternative approach. Here we present a retrospective, open label case-series of pBONT-A’s efficacy and safety regarding neurological consequences involving changes in somatosensory profiles of both responders and non-responders. <b>Methods</b>: Sixty patients (53 ± 13years, 77% males) with PNI were treated with pBONT-A after a test injection with a local anesthetic, which prompted distinctive pain relief. Quantitative Sensory Testing (QST; DFNS-protocol) and pain intensity were assessed before and ≥7 days post pBONT-A injection. Definition of response: satisfactory pain reduction of ≥30% NRS (numerical rating scale: 0 = no pain, 10 = worst pain) for ≥4 days. <b>Statistics</b>: paired t-test, Mann-Whitney-U-test, Χ²-test. <b>Results</b>: A temporary weak paresis in one case was clinically verified. The QST-parameters remained unchanged, but patients with more frequent hyperalgesia signs reported less analgesia (p=.04). The pBONT-A injection prompted pain relief by 24.8% (NRS:6.0 ± 1.7vs.4.5 ± 2.1; p <b>Discussion</b>: Ultrasound-guided pBONT-A injection seems to be a safe treatment leading to a sufficient pain relief for some months without sensory changes. Surprisingly, pBONT-A showed a pronounced analgesic effect also in patients without signs of hyperalgesia.