A Cross Over Pilot Study of Abobotulinum Toxin A (Dysport) as a Treatment for Task-dependent Upper Limb Tremor

Inclusion Criteria:

* Patients with task-dependent essential tremor in upper limb. Tremor is present during at least one of the study functional tasks i. pointing task (touch between nose and a pen held 2 ft. in front. ii. pouring task (cup: pouring water out/in). iii. feeding task (weighted fork from plate on table to mouth). iv. string instrument bowing or holding instrument in static position. v. computer mouse (simple vertical or horizontal movements).
* Patients must be capable of performing informed consent.
* Patients on stable medications for treatment of task-dependent essential tremor for 1 month prior to study entry and maintain them throughout the study.
* Patients previously treated with BoNT of any type must have occurred no sooner than 12 weeks prior to study entry.

Exclusion Criteria:

* Patients with no presence of tremor during study functional tasks.
* Presence of tremor during the functional task is below minimum amplitude required to be considered for injection based upon investigator's clinical judgment.
* Patients with unstable medical conditions or psychiatric conditions.
* Patients with a medical condition that precludes them from receiving BoNT injections.
* Pregnant women, or premenopausal women not willing to use contraceptive measures throughout the duration of the study.
* Lithium, Valproic acid, Amiodarone, typical and atypical neuroleptics. Exposure to other than the listed tremorogenic or potentially tremorogenic drugs is allowed only if, in the opinion of the investigator, this will not interfere with the study drug evaluations.