Botulinum toxin injection, dilution confusion: The impact of toxin diffusion on clinical practice

Botulinum toxins (BoNT) are a standard of care for spasticity management of children with a variety of neuromuscular (NM) conditions. BoNT relaxes skeletal muscles by inhibiting the release of acetylcholine from the neuromuscular junction (NMJ). As part of their training physiatrist become proficient in the targeted injections of BoNT into affected skeletal musculature. While the pharmacology and pharmacokinetics of BoNT are well characterized, there is limited literature on the clinical impact that varying the volume of diluent that a toxin is reconstituted within. In theory, injection of a larger volume of dilute BoNT would allow for a larger spread affect reaching more distant NMJs; the reverse is also be true. Dilution volume of BoNT injections in children produces some unique situations due to their low weight, smaller muscle bulk, an increased relative risk of spread to surrounding structures, and novel differences in concentration of NMJ in immature muscle. Some of these factors may act as guiding principles that providers can use when adjusting from their standard BoNT dilutional practices. Although, there are recommended dosing strategies available each child's spasticity pattern represents a unique situation and providers must be allowed flexibility to think creatively about dilution strategies for BoNT injections.