It is refreshing to read a report on negative outcomes as it reinforces the honesty that is often lacking with the well-known publication bias in medical publications. It is also not common to come across surgical randomised controlled trials (RCTs) involving a placebo arm that provide level 1 evidence, which makes this even more interesting. This double-blind, RCT on 64 men (age 45.9 +/- 11 years) with chronic scrotal pain (mean duration 5.7 +/- 5.7 year history of pain) who had at least temporarily experienced relief from a cord block with local anaesthesia (LA) were randomised to receiving either LA alone (n:32) or LA + 200 units onabotulinum toxin A (n:32). The mean visual analog scale (VAS) pain scores were not significantly changed one month after the blocks and there was no statistically significant difference between the two arms (48% LA only group vs. 55% BTX group). Most men who reported a response following BTX returned to baseline pain levels by three months. Interestingly, an open label trial was offered to the men in the control arm, and data is available on 13 men: 69% demonstrated an improvement in pain scores. Chronic scrotal pain is often a debilitating condition which has a reported prevalence of 3.7-4.75%. Treatment is often unsatisfactory for both the sufferer and the clinician, and when successful often short-lived. Options include non-steroidal and neuropathic pain medication, local anaesthetic blocks, denervation techniques and excision of the epididymis or testis. BTX is thought to suppress several neurotransmitters via a direct non-cholinergic effect on pain afferents, and combine with C-fibre nociceptors to suppress the secretion of neurotransmitters such as substance P, glutamate and CGRP. BTX has been successfully used in various other chronic pain conditions but not been used much in chronic scrotal pain. Interestingly, the authors conducted a pilot study which reported pain relief in 72% at one month and 56% at three months, with return to baseline pain levels by six months. The authors refer to other publications and an unpublished trial which had reported better results as well. Perhaps this study did not have a positive outcome because it was under-powered, but its strength is in its RCT design. As this is the only RCT I know of for this topic and given the encouraging reports of BTX in chronic scrotal pain, a larger well-powered trial is required to resolve the question. This trial also provides useful insight into the strong placebo effect that was observed in the open label phase, which may affect the way we interpret results of future trials on individuals with this condition.
Onabotulinum toxin A (BTX) not helpful for chronic scrotal pain
Reviewed by Jay Khastgir
A randomised, double-blind, controlled trial shows that Onabotulinum toxin A nerve blocks do not provide improved pain control in men with chronic scrotal pain.
CONTRIBUTOR
Jay Khastgir
Princess of Wales Hospital, Bridgend & Swansea University School of Medicine.
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