Objective: To assess changes in botulinum toxin dosing over the course of illness of cervical dystonia.

Background: Muscle specific botulinum toxin injections remains the main and only effective therapy available for the focal dystonias. Over the short term the injections are safe and well tolerated. Typical duration of action is approximately 10 weeks. Botulinum toxin is also required for the duration of the disease which is lifelong. Due to the rarity of this disorder, changes in dosing over the long term use of botulinum toxin remains under studied.

Method: We conducted a retrospective review of patients with cervical dystonia who received botulinum toxin for 7 years. Patients were included if they were diagnosed in our movement disorders clinic, received all their treatment at our centre and were treated with botulinum toxin from diagnosis. Patients were excluded if they had a diagnosis of any other neurological disorders or if they were receiving botulinum toxin treatment for any other condition. Generally, patients have more than one muscle injected so total dose at each therapy session was calculated and tracked over the course of the disease.

Results: 19 patients met our criteria for inclusion within this time period. All patients received 3 monthly botulinum toxin injections. Patients had torticollis or both torticollis and laterocollis. Only 3 patients had associated tremor. Mean toxin dosing at presentation was 123u (range 75u to 250u). Two patients had a decrease in toxin dosing between diagnosis and 7 years. 17 patients had an increase in toxin dosing with a mean dose increase of 70 units.

Conclusion: The vast majority of patients require an increase toxin doses during the course of the disease. Cervical dystonia is a chronic illness, dose increases have major implications- botulinum toxin is a dose limited therapeutic option. Identifying the cause for dose increases and alternative options would be prudent in mitigating risk of toxicity and improving outcomes.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/changes-in-botulinum-toxin-dosing-in-cervical-dystonia-over-7-years/