Strategies to decrease injection site pain in botulinum toxin therapy

Botulinum toxin is now used for numerous indications including dystonias, spasticity, cerebral palsy, hyperhidrosis, cosmetics and chronic migraine. It has to be injected into its target tissues thus causing injection site pain. We wanted to compare the efficacy of various analgesic interventions suggested for reduction of injection site pain. In 13 healthy controls, pain thresholds in the fingertips II and III bilaterally were determined by the Mechanical Pain Threshold Test and the Repetitive Pain Stimulation Test at baseline and under nitrous oxide/oxygen, ice spray, local anaesthetic cream and forearm ischaemia. All interventions studied produce statistically significant and robust elevations of the pain threshold in both tests. Nitrous oxide/oxygen had stronger effects than the other interventions, although this superiority was statistically significant only in the Repetitive Pain Stimulation Test and not against ice spray. Also considering duration, localisation and penetration depth of analgesic effects, hyperhidrosis treatment may benefit from nitrous oxide/oxygen, ice spray and local anaesthetic cream. In palmar hyperhidrosis, forearm ischaemia is possible and also reduces botulinum toxin washout. Cosmetic indications may also benefit from nitrous oxide/oxygen and local anaesthetic cream. For botulinum toxin therapy of spasticity, dystonia and tremor, only nitrous oxide/oxygen may offer intramuscular analgesic effect. Its systemic and prolonged effect is also an advantage in injections in several body parts. Future studies are necessary to test the influence of penetration depth and combinations of analgesic interventions.