Objective: To report a case of hypersensitivity reaction to abobotulinumtoxinA injections for spasticity in a patient who did not have hypersensitivity to onabotulinumtoxinA and raise awareness regarding potential unique adverse events among toxin types.

Background: Botulinum toxins (BTX), neurotoxins derived from Clostridial species of bacteria, decrease neurotransmitter release at the neuromuscular junction by inhibiting exocytotic mechanisms. There are different serotypes and BTX type A (BTX-A) binds to and cleaves the SNARE protein to inhibit acetylcholine release. BTX has been proven an effective and safe drug for a variety of neurologic indications. OnabotulinumtoxinA and abobotulinumtoxinA both have BTX-A as the active neurotoxin. However the purification processes are different and contribute to differences in dose ratios, distribution of clinical effects, and the risk of hypersensitivity reactions.

Method: A 29-year-old man with past medical history of spastic quadriplegia cerebral palsy presented to movement disorders clinic for BTX injections for the management of his spasticity. He began receiving injections in 2019 with onabotulinumtoxinA but had to switch formulations to abobotulinumtoxinA six months prior due to insurance coverage issues. 1000 units of abobotulinumtoxinA were reconstituted in 4 mL of sterile, preservative free normal saline. The sites were cleaned and prepped using usual sterile techniques. Several minutes following the injections, he developed localized pruritus and a macular, erythematous rash around all injection sites. He remained hemodynamically stable. His symptoms improved in several hours after a dose of oral antihistamine.

Results: BTX has immunogenic potential that may differ between the formulations. Both onabotulinumtoxinA and abobotulinumtoxinA consist of purified toxin, and a binding protein. However, abobotulinumtoxinA also has cow’s milk protein which can potentially cause a hypersensitivity reaction. Our patient had no prior known allergy to cow’s milk protein, but developed an allergic skin reaction to abobotulinumtoxinA during his third injection cycle. He will be resumed on onabotulinumtoxinA injections going forward.

Conclusion: While hypersensitivity reactions to BTX can occur, the reasons for skin rash remain largely unknown and may differ between the formulations. Providers should be aware of possible idiosyncratic and serious systemic reactions that may necessitate changing formulations of BTX.

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References: Brüggemann, N., Dögnitz, L., Harms, L., Moser, A., & Hagenah, J. (2009). Skin reactions after intramuscular injection of Botulinum toxin A: a rare side effect. BMJ case reports, 2009, bcr09.2008.0942. https://doi.org/10.1136/bcr.09.2008.0942
Walker, T. J., & Dayan, S. H. (2014). Comparison and overview of currently available neurotoxins. The Journal of clinical and aesthetic dermatology, 7(2), 31–39.
Mariana Figueiroa Careta, Livia Delgado, Régia Patriota, Report of Allergic Reaction After Application of Botulinum Toxin, Aesthetic Surgery Journal, Volume 35, Issue 5, July 2015, Pages NP102–NP105, https://doi.org/10.1093/asj/sju105

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MDS Abstracts - https://www.mdsabstracts.org/abstract/hypersensitivity-reaction-to-abobotulinumtoxin-a-case-report/