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myoclonus
Etiology:
1) hypoxia, anoxia
- syncope
2) lipid storage disease
3) encephalitis, viral encephalitis
4) myelitis
5) metabolic encephalopathy due to
a) respiratory failure (post-hypoxic myoclonus)
b) chronic renal failure, uremia
c) hepatic failure, asterixis
d) electrolyte imbalance
e) toxic serotonin syndrome
6) neurodegenerative disease
a) Alzheimer's disease
b) Creutzfeldt-Jakob disease
c) corticobasal ganglionic degeneration
7) paraneoplastic disorders
- oposclonus-myoclonus
8) tetanus
9) seizures, epilepsy
a) tonic-clonic seizure
b) myoclonic epilepsy
10) sleep states
a) hypnic jerks
b) nocturnal myoclonus
c) hiccup
11) nerve compression [2]
12) pharmaceuticals
- valacyclovir
13) occasionally normal action
Pathology:
- sustained myoclonus generally indicates upper motor neuron disease
Clinical manifestations:
- very brief, involuntary, random muscle contracture & relaxation in rapid succession
- shock-like, jerky movements [3]
- brief lapses in muscle tone may result in loss of balance [3]
- may occur spontaneously at rest, in response to sensory stimuli, or with voluntary movements
- may involve a single muscle unit or a group of muscles
Differential diagnosis:
- dystonia: twisting & posturing, no lapses in muscle tone
Management:
1) agents of choice
- valproate (Depakote)
- clonazepam
- levetiracetam
- zonisamide
- topiramate [2] 2 Alternative agents
- phenobarbital
- baclofen
Related
paraneoplastic opsoclonus myoclonus ataxia; Kinsbourne syndrome; myoclonic encephalopathy of infants; dancing eyes-dancing feet syndrome
Specific
myoclonic dystonia; alcohol-responsive dystonia; dystonia-11
myoclonic seizure
nocturnal myoclonus (periodic limb movement disorder, PLMD, periodic limb movements of sleep, PLMS)
posthypoxic myoclonus (Lance-Adams syndrome)
General
movement disorder
musculoskeletal sign/symptom
References
- Harrison's Principles of Internal Medicine, 13th ed.
Isselbacher et al (eds), McGraw-Hill Inc. NY, 1994, pg 122
- Medical Knowledge Self Assessment Program (MKSAP) 11, 16, 17, 18, 19.
American College of Physicians, Philadelphia 1998, 2012, 2015, 2018, 2021
- Medical Knowledge Self Assessment Program (MKSAP) 19
Board Basics. An Enhancement to MKSAP19.
American College of Physicians, Philadelphia 2022
- Mills K, Mari Z.
An update and review of the treatment of myoclonus.
Curr Neurol Neurosci Rep. 2015 Jan;15(1):512. Review.
PMID: 25398378
- National Institute of Neurological Disorders and Stroke (NINDS)
NINDS Myoclonus Information Page
https://www.ninds.nih.gov/Disorders/All-Disorders/Myoclonus-Information-Page