Objective: To describe the case of a patient with limb myorhythmia successfully treated with bolutinum toxin injections.

Background: 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, anticonvulsant or dopaminergic agents showing limited efficacy.

Method: We review relevant clinical history, laboratory values, imaging, electromyographic data, and clinical course.

Results: The patient is a 30-year-old male evaluated for abnormal movements of the left lower leg that began after an ankle injury. After a few years of persistent symptoms, the patient underwent Achilles tendon scar tissue debridement without improvement in movements. Normal neuroimaging prompted a referral to the Neurology clinic for further evaluation. On examination, he had near-constant involuntary, slow, rhythmic flexion/extension tremor of toes 2-4; there were no sensory or strength deficits, appendicular or central ataxia, or upper motor neuron signs. The movements were diminished during active movement. Needle 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 an EMG-guided chemodenervation procedure with Incobotulinum toxin A injection on the left flexor digitorum brevis. At three months follow-up, he had achieved a sustained 40-50% reduction in the intensity of the movements and improved quality of life.

Conclusion: Myorhythmia is a rare movement disorder with a proposed central etiology. Evaluation is aided by EMG, which can also identify targets for chemodenervation in medication-refractory cases.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/limb-myorhythmia-treated-with-chemodenervation-a-case-report/