Limb myorhythmia treated with chemodenervation: a case report.

We describe a case of limb myorhythmia successfully palliated with botulinum toxin injections. The patient is a 30-year-old male evaluated for abnormal movements of the left lower foot that began after an ankle injury for which the patient underwent Achilles tendon scar tissue debridement without improvement. On examination, he had near-constant involuntary, slow, rhythmic flexion/extension tremor of toes 2-4 that was diminished during active movement. Needle electromyography (EMG) revealed a rhythmic, 2-3 Hz tremor isolated to the flexor digitorum brevis. After failure of medical management with muscle relaxants, gabapentin, and levodopa trials, the patient underwent two EMG-guided chemodenervation procedures with incobotulinum toxin A injections of the left flexor digitorum brevis. At 3-month follow-up, he had achieved a sustained 50% reduction in the intensity of the movements and improved quality of life. Myorhythmia is a rare condition characterized by a repetitive, rhythmic, slow frequency (1-4 Hz) movement affecting the cranial and limb muscles. The most common causes include stroke, demyelinating disorders, drug or toxin intake, trauma, and infections. The management of this condition is very limited with pharmacologic agents such as anticholinergics, antispasmodics, anticonvulsants, or dopaminergic agents showing limited efficacy. The use of botulinum toxin chemodenervation aided by EMG muscle targeting can be a useful therapeutic intervention in cases of medication-refractory regionally distributed myorhythmia involving accessible muscles.