Myoclonus is a clinical sign that is characterized by
brief, shocklike, involuntary movements caused by
muscular contractions or inhibitions .
Muscular contractions produce positive myoclonus,
muscular inhibitions produce negative myoclonus
Patients will usually describe myoclonus as
consisting of "jerks," "shakes," or "spasms."
ANATOMIC AND PHYSIOLOGIC CLASSIFICATION
classified by the localization of the physiologic
mechanism that generates it
focal discharge from the primary sensorimotor cortex causes myoclonic jerk
Occurs because of insufficient inhibition within neuronal circuits of the
primary motor cortex, primary sensory cortex, or both
Rapid generalization - can produce myoclonic seizures in certain epileptic
may occur with
reflex sensory stimulation (cortical reflex myoclonus),
Muscle activation (cortical action myoclonus),
with rest (eg, focal motor seizure),
or any combination
involves abnormal, paroxysmal, and excessive oscillation in
bidirectional connections between cortical and subcortical sites.
is the major mechanism for myoclonic seizures in primary
generalized epileptic syndromes (JME) and others (eg,
Eg: in JME and absence epilepsy, thalamic networks
abnormally couple with widespread cortical areas to produce
excessive neuronal activity
The resulting myoclonic jerks are commonly generalized or
myoclonus is generated from a site that is subcortical, but
myoclonus manifests far beyond segments that are near the
Eg. reticular-reflex myoclonus and propriospinal
abnormal activity begins in a focal area of neuraxis and then
spreads in both rostral and caudal directions, producing
generated at a particular segment or contiguous segments
of brainstem and/or spinal cord.
Freq. of motor oscillations < tremor.
manifests at, or close to, that particular segment or
contiguous segments of the body
spinal segmental myoclonus
arises d/t peripheral nervous system lesion
produces hyperactive motor discharges to its muscle
(eg, hemifacial spasm).
CLINICAL AND ETIOLOGIC CLASSIFICATION
classification scheme of Marsden and colleagues
● Secondary (symptomatic)
Physiological: Jerks associated with sleep
occur during sleep or sleep transitions
Partial myoclonic jerks – multifocal, s/i distal muscles
Massive myoclonic jerks – hypnic- gen., affect trunk and proximal
Periodic movements of sleep (nocturnal myoclonus) are stereotyped
repetitive dorsiflexion of toes and feet, sometimes with flexion of knees
divided into sporadic and hereditary
myoclonus is the most prominent or only clinical finding - ie, an
Sporadic (or idiopathic) essential myoclonus - heterogeneous w.r.t.
distribution, exacerbating factors, CNS findings
often 2o to brainstem and/or cerebellar lesion.
However, some patients have no apparent structural lesion - essential
myoclonus is c/b contractions of the tensor veli palatini
secondary (symptomatic) c/b contractions of levator veli palatini.
Hereditary essential myoclonus
demonstrates a subcortical-nonsegmental physiology
Onset < 20 yrs
benign course - active life and normal lifespan
Absence of cerebellar ataxia, spasticity, dementia, and seizures
occurs throughout arms & axial muscles.
exacerbated by muscle activation
markedly diminished with alcohol ingestion.
Is myoclonus in the setting of epilepsy
cortical or cortical-subcortical physiology
Seizures dominate the clinical picture
idiopathic, genetic, or a static encephalopathy
Myoclonus can occur as
one of several components of a seizure
the only seizure manifestation - myoclonic seizure
one of multiple seizure types within an epileptic syndrome
Familial cortical myoclonic tremor with epilepsy
Autosomal dominant inheritance
Distal action tremor and myoclonus
Infrequent, 2o GTCS
Relatively benign course, typically normal cognition
Responsiveness to anticonvulsants
Symptomatic (secondary) myoclonus
occurs as a secondary symptom of neurologic or non-
to control myoclonus - treat the underlying disorder
may reverse certain myoclonus
myoclonus caused by an acquired abnormal metabolic state
medication or toxin
Evidence base for treatment is mainly of observational case series and case
Drug treatment – aim is to augment inhibitory processes within
Levetiracetam, piracetam- initial drugs
clonazepam and valproic acid – add on’s
Gait disturbance - most resistant to treatment.
An unsteady gait with frequent falls may persist despite control
of action and reflex myoclonus in UL
Also, there is no consistent evidence for benefit in negative
Includes the myoclonus in PGE
Treatment is that of epilepsy
Standard antiepileptic treatments- not helpful
In addition, increased risk of alcoholism in patients with
essential myoclonus (including myoclonus-dystonia) because
condition is ethanol-responsive.
initial treatment with clonazepam
Benztropine or trihexyphenidyl – alternatives for initial or add-
on therapy in essential myoclonus, including myoclonus-
Zonisamide- propriospinal myoclonus.
clonazepam (up to 6 mg daily)
However, benefit - limited.
Alternatives- levetiracetam, botulinum toxin injection,
carbamazepine, diazepam, and tetrabenazine.
Palatal myoclonus –
botulinum toxin injections as initial treatment for debilitating palatal
pharmacologic interventions- no benefit
possibly useful drugs :
clonazepam, piracetam, valproic acid, baclofen, carbamazepine,
lamotrigine, phenytoin, sumatriptan, and tetrabenazine.
botulinum toxin injection hemifacial spasm and
other peripheral myoclonus
carbamazepine may have some effect.