Table 1
Distinguishing features of myoclonus and other movement disorders.
| MYOCLONUS | TICS | DYSTONIA | TREMOR | CHOREA | |
|---|---|---|---|---|---|
| Duration/Cadence | Very brief, shock-like | Brief | Sustained, longer duration | Sustained, longer duration | Could be brief |
| Onset | Abrupt | Abrupt | Gradual | Gradual | Rapid |
| Reflex | Frequent | Premonitory urge | May be kinesigenic | Rest, postural, or action | No |
| Termination | Abrupt | Abrupt | Progressive | Progressive | Progressive |
| Suppressibility | No | Temporary | No | Temporary | No |
| Pattern | Simple | Simple/complex | Multiplanar complex | Sinusoidal, rhythmic | Flows from one body part to another |
| Neurophysiological testing | Back-averaging EEG potentials preceding EMG | Organization of the movement | May be useful for treatment | EMG/NCS can distinguish action tremor from myoclonus | Unhelpful |
Figure 1
CONSORT (Consolidated Standards of Reporting Trials) flowchart detailing study sample size and exclusion criteria.
Figure 2
Bar graph detailing number of cases per identified etiology for myoclonus in the inpatient (red) and outpatient (green) settings. The total number of inpatient charts reviewed was 279 individuals, whereas the total number of outpatient charts reviewed was 85 individuals. Almost half of studied cases in the inpatient setting had one probable etiology, whereas the remainder had 2 or more probable etiologies. More than half of the outpatient cases exhibited a singular probable etiology.
Table 2
Sample of final diagnoses encountered per class of etiology in inpatient and outpatient settings incorporating the IAPRD 2025 consensus classification.
| ETIOLOGY | DIAGNOSES |
|---|---|
| Metabolic (non-genetic) | Hepatic encephalopathy Uremic encephalopathy Hyponatremia Hyperglycemic non-ketotic state Diabetic ketoacidosis Dialysis disequilibrium syndrome |
| Toxic/drug-induced (iatrogenic) | Gabapentin-induced myoclonus Sertraline toxicity Budesonide/formoterol toxicity Quetiapine toxicity Phenytoin-induced myoclonus Tramadol-induced myoclonus Opiate/narcotic withdrawal Alcohol withdrawal |
| Nervous system lesions (cerebral hypoxic-ischemic) | Cerebrovascular disease (post-stroke) Lance-Adams myoclonus Anoxic brain injury Intraparenchymal hemorrhage Hypoxic-ischemic encephalopathy |
| Nervous system lesions (spinal) | Cervical spinal stenosis Propriospinal myoclonus |
| Progressive (neoplastic) | Cerebral meningioma Intracranial metastases T-Cell lymphoma |
| Neurodegenerative disease | Parkinson’s Disease Multiple System Atrophy Dementia with Lewy Bodies Corticobasal ganglionic degeneration Frontotemporal dementia Tuberous sclerosis Essential tremor with myoclonus |
| Infectious/post-infectious | Urinary tract infection Septic encephalopathy COVID-19 pneumonia Creutzfeldt-Jakub Disease Transverse myelitis |
| Epileptic (static) | Juvenile-onset myoclonic epilepsy Myoclonic status epilepticus Symptomatic epilepsy with myoclonus |
| Functional | Psychogenic non-epileptic spells (PNES) Functional myoclonus-like movement disorder |
| Physiologic | Singultus (hiccups) Hypnagogic myoclonus |
| Idiopathic | Essential myoclonus |