Rare diseases · Sign or symptom
Myoclonus
HP:0001336
What it means
Very brief, involuntary random muscular contractions occurring at rest, in response to sensory stimuli, or accompanying voluntary movements.
Myoclonus may be synchronous (several muscle contracting simultaneously), spreading (several muscles contracting in sequence), or asynchronous (several muscles contracting with varying and unpredictable relative timing). Myoclonus is characterized by sudden unidirectional movement due to muscle contraction (positive myoclonus) or due to sudden brief muscle relaxation (negative myoclonus). Electrophysiological tests are very helpful in determining whether myoclonus is cortical, subcortical or spinal.
Rare diseases that can present with this123
Very common80–99%
18- 9p13microdeletion syndrome
- ABeta amyloidosis, Iowa type
- Corticobasal syndrome
- Early-onset autosomal dominant Alzheimer disease
- Encephalopathy due to prosaposin deficiency
- Familial adult myoclonic epilepsy
- Fatal familial insomnia
- Hereditary hyperekplexia
- Infantile epileptic spasms syndrome
- Myoclonus-dystonia syndrome
- Opsoclonus-myoclonus syndrome
- PRDM8-related progressive myoclonus epilepsy
- Progressive myoclonic epilepsy type 1
- Progressive myoclonic epilepsy with dystonia
- Sialidosis type 1
- Spinal muscular atrophy-progressive myoclonic epilepsy syndrome
- Subacute sclerosing leukoencephalitis
- Whipple disease
Common30–79%
43- 3-methylglutaconic aciduria-neonatal cataract-neurologic involvement-congenital neutropenia syndrome
- Adult-onset cervical dystonia, DYT23 type
- Alpers-Huttenlocher syndrome
- Alpha-N-acetylgalactosaminidase deficiency type 1
- Atrioventricular defect-blepharophimosis-radial and anal defect syndrome
- Autosomal recessive dopa-responsive dystonia
- Autosomal recessive spastic ataxia-optic atrophy-dysarthria syndrome
- Autosomal recessive spastic paraplegia type 48
- Caribbean parkinsonism
- CLN12 disease
- Dentatorubral pallidoluysian atrophy
- Dravet syndrome
- Early-onset progressive encephalopathy-hearing loss-pons hypoplasia-brain atrophy syndrome
- Early-onset spastic ataxia-myoclonic epilepsy-neuropathy syndrome
- Familial dyskinesia and facial myokymia
- FOXG1 syndrome
- Huntington disease
- Inherited Creutzfeldt-Jakob disease
- Juvenile absence epilepsy
- Kufor-Rakeb syndrome
- Lathosterolosis
- Lennox-Gastaut syndrome
- MELAS
- Myoclonic epilepsy of infancy
- Myoclonus-cerebellar ataxia-deafness syndrome
- Nipah virus disease
- Parkinsonian-pyramidal syndrome
- Paternal uniparental disomy of chromosome 1 syndrome
- Pontocerebellar hypoplasia type 4
- Progressive encephalopathy-severe neurodegeneration-lipodystrophy syndrome
- Progressive myoclonic epilepsy type 3
- Pyridoxamine-5-phosphate deficiency-developmental and epileptic encephalopathy
- Riboflavin transporter deficiency
- Sandhoff disease, infantile form
- Sensory ataxic neuropathy-dysarthria-ophthalmoparesis syndrome
- Serotonin syndrome
- Spinocerebellar ataxia type 37
- Spinocerebellar ataxia with epilepsy
- Sporadic Creutzfeldt-Jakob disease
- Stiff person spectrum disorder
- Sudden infant death-dysgenesis of the testes syndrome
- Thyrocerebrorenal syndrome
- X-linked dystonia-parkinsonism
Sometimes5–29%
19- 3-hydroxy-3-methylglutaric aciduria
- 6-pyruvoyl-tetrahydropterin synthase deficiency
- Alacrimia-choreoathetosis-liver dysfunction syndrome
- Angelman syndrome
- Angelman syndrome due to maternal 15q11q13 deletion
- Ataxia-telangiectasia-like disorder
- Atypical Gaucher disease due to saposin C deficiency
- Atypical juvenile parkinsonism
and 11 more in this range
The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
Also called: Involuntary jerking movements · Jerking · Myoclonic jerks
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Start free with EleplanThis page uses the Human Phenotype Ontology (2026-06-23) — Human Phenotype Ontology Consortium, hpo.jax.org. Disease associations from Orphanet (INSERM), CC BY 4.0. Content is educational and is not medical advice.