Incobotulinumtoxina Improves Dystonic Signs and Modulates Cortical Plasticity in Focal Hand Dystonia

Background: Botulinum toxin (BoNT) is an accepted treatment for focal hand dystonia (FHD) but the effects of incobotulinumtoxinA have not been reported. The central mechanisms of action of BoNT are not fully understood. Animal models have shown deficient depotentiation in corticostriatal networks but this has not been explored in FHD. Objective: To study depotentiation in FHD patients and correlate with the clinical effects of BoNT treatment. Methods: We studied 7 FHD (5 writer's cramp and 2 musician's dystonia) patients (age: 57 ± 3 years, 2 women) with established response to BoNT. They were studied at baseline (four months after last BoNT injection), one and three months after treatment with incobotulinumtoxinA with FHD scores and a potentiation-depotentiation protocol. Motor-evoked potential (MEP) amplitude was measured at baseline and after five different time intervals up to 30 min after the potentiation-depotentiation protocol. Results: FHD patients had baseline writer’s/musician cramp rating scale scores of 14.3 ± 2.1, which decreased to 12.6 ± 2.3 (p = 0.02) at one month post-injection and to 12.7 ± 2.5 (p = 0.03) at three months post-injection assessed by a blinded rater. Potentiation was decreased in patients at baseline and inhibition was observed at one month after BoNT injection, when peak effect is found. There was depotentiation in patients at baseline and at 3 months post incobotulinumA injection, but potentiation at 1 month after injection. Conclusions: Our preliminary findings suggest that incobotulinumtoxinA treatment improves dystonia scores and modulates cortical plasticity in FHD. Depotentiation may be related to its therapeutic effect. This is ongoing study with more patients being recruited.