Botulinum toxin dosing in arm muscles: contextual factors.

Botulinum toxin (BT) has been successfully used for many years to treat various muscle hyperactivity disorders including dystonia and spasticity. Its dosing is guided by dosing tables describing target muscles and dose ranges. To refine the BT dosing, we wanted to analyse how contextual factors may influence the injector's final dosing decision.In a retrospective review of real-life data of 1170 BT treatments, we studied the influence of various contextual factors on the BT doses in 21 arm muscles of 252 patients receiving BT therapy for different muscle hyperactivity disorders.We found that BT arm doses are significantly higher in treatment of spasticity than in treatment of dystonia. We also found that spontaneous arm dystonia requires higher BT doses in a proximal application pattern, whereas task specific writer's cramp requires considerably reduced BT doses with a distal application pattern. Injections of non-arm muscles influence the BT dosing in arm muscles only marginally.Our study demonstrates that BT dosing does not only depend on the particularities of the individual target muscle injected, such as its volume and its static or phasic function. BT dosing and its application pattern rather depend on additional contextual factors such as the aetiology and pathophysiology of the muscle hyperactivity treated. These contextual factors need to be included in dosing tables and may improve the outcome of BT therapy.