"Off" painful dystonia in Parkinson's disease treated with botulinum toxin.

The "off" painful dystonia (OPD), usually concerning the feet, is a type of abnormal involuntary movement, induced by the chronic use of levodopa. It is mostly observed in the advanced stage of Parkinson's disease (PD), particularly in the early morning, in the evening, and late at night. Indeed, some patients have experienced OPD also during "on" periods when dystonic posture of the foot alternates with dyskinesia. The pain probably is due to sustained muscle contraction, which causes prolonged muscle spasm, as in primary dystonia or torticollis. Dopaminergic drugs like bromocriptine, pergolide, and especially apomorphine (s.c. infusions, or bolus), can dramatically improve the OPD. Anticholinergics baclofen and lithium are alos used in the management of OPD with some benefit. On the other hand, clinical experience shows that in many cases, these therapeutic procedures are not always enough to produce the expected results. Thirty PD patients (22 men and eight women) with OPD of the foot were treated with botulinum toxin (Botox, Btx) using electromyograms to guide injections. Dystonia was evaluated using a quantitative rating scale. The selection of the muscles for Btx treatment was carried out on the basis of foot posture. We injected Btx into tibialis posterior, tibialis anterior, gastrocnemius, flexor digitorum longus, and extensores hallucis longus with a median dose 40 IU for each muscle, distributed in two sites. In all patients, the pain improved within 10 days, whereas in 21 patients, the pain disappeared completely for 4 months (range, 3-7 months); a concomitant improvement in intensity of the dystonic spasm was also observed. No side effects were reported. Seven patients with associated "on" foot dystonia described an improvement of foot posture on walking. In conclusion, in this uncontrolled study, the use of Btx in OPD seemed a promising tool to improve pain linked to foot dystonia; however, because of the well-known underlying dopaminergic defect in OPD, the Btx therapy should be considered only if the dopaminergic treatment established for the management of OPD has failed.