Background: Acquired generalized repetitive myoclonus may be mistaken for tremor. Distinguishing myoclonus has etiologic and therapeutic implications.
Objective: To describe isolated generalized polymyoclonus and the outcomes of etiologic evaluations at the time of diagnosis.
Design: Computer search of the Mayo Movement Neurophysiology Laboratory database and medical records linkage system.
Setting: Department of Neurology, Mayo Clinic.
Patients: Nineteen adults with generalized repetitive myoclonus confirmed using surface electromyography (burst duration <50 milliseconds), and other neurologic features minimal or absent.
Interventions: Treatment of myoclonus and underlying causes.
Main outcome measures: Clinical presentation and underlying etiologies.
Results: We identified 19 patients with isolated generalized polymyoclonus resembling whole-body tremor. Onset was most often subacute (12 patients), mean symptom duration was 1.8 years, and mean age at onset was 55 years. Referral diagnoses or patient complaints were tremor, tremulousness, or shaking in all but 5 patients. All the patients had repetitive myoclonus of all limbs, impairing gait in 14 patients. Surface electromyography confirmed nonperiodic muscle burst durations of less than 50 milliseconds, typical of myoclonus. Clinical and serologic screening for cancer and autoimmunity revealed metastatic breast cancer in 2 patients (1 positive for ganglionic acetylcholine receptor antibody) and antibody profiles implicating neurologic autoimmunity in 3 patients (CRMP-5 IgG or neuronal voltage-gated potassium channel antibodies). Medications known to occasionally trigger myoclonus (opioids, selective serotonin reuptake inhibitors, and a serotonin-norepinephrine reuptake inhibitor) were being taken by 7 patients. Myoclonus resolved after discontinuation of selective serotonin reuptake inhibitor therapy in 1 patient; drug discontinuation was declined and follow-up was inadequate in the other 6.
Conclusions: Isolated whole-body tremulousness should raise the suspicion of generalized polymyoclonus, confirmed using routine surface electromyography. Recognition is important because the differential diagnosis includes autoimmunity and drug-induced myoclonus.