14.5. Myoclonus
- General considerations
- Definition: very rapid, brief shock like jerks:
- May involve small muscle of the entire body
- Discrete and not random
- Produced by a brief positive muscle contraction
- Negative myoclonus: brief lapse of posture
- May originate anywhere in the neuraxis: cortex, cerebellum, basal ganglia, brainstem (nucleus gigantocellularis) occurs in normal individuals
- Precipitated by sensory stimulation
- Rhythmic myoclonus most often caused by brainstem or spinal cord disease
- Marsden's classification:
- Physiologic
- Essential
- Epileptic
- Symptomatic
Physiologic Myoclonus
- General considerations:
- Occurs in normal individuals
- Hyperexcitable neurons of the cortex
- Clinical features of sleep myoclonus:
- Sleep most common physiologic myoclonus:
- Sudden movements during sleep or sleep transition
- Massive myoclonic jerks (hypnic)
- Partial jerks:
- Multifocal
- Distal limb muscles
- Hypnic jerks:
- Affect the trunk and proximal extremities
- Generalized
- Noted prior to major motor seizures:
- May increase 1–2 weeks prior to a seizure
- Nocturnal myoclonus:
- Repetitive stereotyped dorsiflexion of the toes and foot
- Flexion of the knees and hip
- Associated with restless leg syndrome
- May disrupt sleep
- Occurs during non-REM sleep
- Lasts 1.5–2.5 seconds
- Increased incidence in patients with daytime drowsiness and insomnia
Other Forms of Physiologic Myoclonus
- Induced by
- Anxiety
- Exercise
- Hiccough (diaphragmatic myoclonus)
Essential Myoclonus
- General considerations:
- Normal neurologic examination
- Onset prior to age 20
- AD or sporadic with variable penetrance
- Benign course with normal life expectancy
- Clinical features:
- Normal EEG
- Normal neurologic exam
- Striking response to alcohol
- Distributed throughout the upper body
- Exacerbated by movement
Epileptic Myoclonus
- General considerations:
- Myoclonus in patients with a seizure disorder
- Probably of cortical origin
- May occur as one component of the seizure or as its only manifestation
- May be one seizure type among several in the individual patient
- Clinical features:
- Older children and adolescents:
- Photosensitive epileptic myoclonus
- Myoclonic absences
- Associated with primary generalized epilepsy
- Adults:
- A proportion of adults with primary generalized epilepsy have morning myoclonic jerks
- May be interictal in primary generalized epilepsy
- Myoclonic jerks increase (particularly nocturnal) in 25% of patients prior to seizures
- Components of epilepsy:
- Isolated epileptic myoclonic jerks
- Photosensitive myoclonus
- Stimulus sensitive myoclonus
- Epilepsia partialis continua
- Childhood myoclonic epilepsies
Childhood Myoclonic Epilepsy
- Infantile spasms
- Lennox–Gastaut Syndrome
- Aicardi's syndrome
- Benign familial myoclonic epilepsy (Rabot)
- Myoclonic epilepsy of Janz
Progressive Myoclonic Epilepsy of Unverricht Lundborg–Baltic Myoclonus
- General considerations:
- AR (Finnish families) EPM1 gene
- Encodes cystatin B that inhibits cathepsins
- Clinical features:
- Onset age 7–10 years of age
- Myoclonus provoked by:
- Attempted movement
- Light, noise, touch
- Seizures:
- Major motor
- Rare atonic or absence attacks
- Dementia
- Dysarthria
- Spasticity in 25%
- Ataxia (loss of Purkinje cells)
- EEG:
- Generalized spike and wave discharges with photosensitivity
Symptomatic Myoclonus
- General considerations:
- Myoclonus occurs in the setting of an underlying disease
- Encephalopathy is prominent
- Progressive disease process
- Storage diseases are prominent
Specific Diseases with Major Symptomatic Myoclonus
Lafora Body Diseases
- General:
- Clinical features:
- Childhood or adolescent onset
- Seizures (generalized tonic-clonic) in adolescence
- Dementia (more severe than in Baltic myoclonus)
- Myoclonus (resting and action)
- Visual seizures occur in 50% of patients:
- Simple hallucinations
- Scotomata
- Occipital complex partial seizures
- Fluctuating course with periods of cortical pseudo blindness
- Death occurs 2–10 years after the onset of symptoms
Ceroid Lipofuscinosis (Batten's Disease)
- General considerations:
- AR; chromosome/genes for adult form CLN4 are unknown
- 10–20% of patients are variants of the core disease
- Infantile adolescent and adult forms
- Probably the most common of the lysosomal storage diseases
- Clinical features:
- Myoclonic seizures
- Pyramidal signs
- Dementia
- Pathology:
- Lipofusion pigments in all areas of the neuraxis
- Curvilinear, finger print structure; some patients with osmophilic granules in the brain
Tay–Sach's GM2 Gangliosidosis
- General considerations:
- AR; hexosaminidase A enzyme deficiency
- Clinical features:
- "Cherry red spot" in the retina
- Dementia
- Blindness
- Deafness
- Stimulus sensitive myoclonus
Sialidosis
- General considerations:
- Clinical features:
- Initial intention tremor and dysarthria
- Progressive ataxia
- Epilepsy is common, but not invariant
- Myoclonus:
- Develops later
- Worse with intention
- May move the extremity in the opposite direction of that intended
- Krabbe's Disease
- Ramsay Hunt Syndrome
- Friedreich's Ataxia
- Ataxia telangiectasia (myoclonus is common)
- Wilson's Disease
- Torsion Dystonia
- DRPLA
- Corticobasal degeneration (rare myoclonus)
- Parkinson's disease (rare myoclonus)
- Huntington's disease
- Multisystem atrophy (rare myoclonus)
- Hallervorden Spatz (PANK2)
- PSP (rare)
- Creutzfeldt Jacob disease (diagnostic)
- Alzheimer (rare, except in late stage)
- Diffuse Lewy body disease (rare, except in late stage)
- Subacute sclerosing pass encephalopathy
- Herpes simplex (seizures>myoclonus)
- HIV related (rare)
- Post infectious autoimmune disease (ADEM)
- Dialysis dysequilibrium syndrome
- Hypoglycemia (seizures more common)
- Hepatic failure (asterixis more frequent)
- Renal failure (common)
- Hyponatremia (lethargy » myoclonus)
- Von-Ketotic hyperglycemia (segmental myoclonus is almost diagnostic)
- Multiple carboxylase deficiency
- Mitochondrial diseases (MERRF most common)
- Biotin deficiency (seizures predominate)
- Lance–Adams syndrome (postural kinetic tremor; tremor with intention predominate)
- Post traumatic (seizures; cognitive decline)
- Posthypoxic (Lance–Adams Syndrome; rubral tremor predominates)
- Heat stroke (DIC, cardiac and renal failure)
- Electric shock (cardiac arrest) CRPS supervenes if patient survives
- Tumor (nucleus gigantocellularis; rare)
- Herpes zoster (brainstem inflammation)
- Post thalamotomy (Voa, Vop, Vim, thalamic nuclei are involved)
- Mollaret's triangle (dentato-olivary-rubral connections; interrupted by stroke)
- Celiac disease (peripheral neuropathy and myopathy predominate)
- Whipple disease (myoarrthymia of the jaw, with large joint arthritis and malabsorption syndrome are diagnostic)
- Paraneoplastic syndrome (neuropathy and cerebellar degeneration predominate)
Miscellaneous Toxins That Cause Myoclonus
- Bismuth:
- Encephalopathy
- Myoclonus
- Anterior horn cell death with weakness and fasciculation
- Severe spongiosis of layer 5 of the motor cortex
- Methylbromide (rash)
- Mercury (concomitant cognitive cerebellar and basal ganglia disease)
Categories of Processes Associated with Myoclonus in Adulthood
- Marden Classification
- Physiologic
- Essential myoclonus
- Epileptic myoclonus
- Components of seizures
- Progressive myoclonic epilepsies
- Secondary myoclonus
- Ataxic syndromes
- Basal ganglia diseases
- Ataxias
- Myoclonus with Dementia
- Viral encephalitis
- Metabolic abnormalities
- Associated with toxins and drugs
- Damage to the CNS
Asterixis (Negative Myoclonus)
- General considerations:
- Definition: sudden brief loss of postural tone usually in extension of the wrist and hand; may be elicited with flexion and abduction of the thighs
- Related to dysfunction of the nucleus gigantocellularis of the brainstem
- Bilateral asterixis:
- Usually metabolic in origin
- Bilateral structural lesions of the mid pons or mesencephalon
- Unilateral asterixis:
- Metabolic or toxic process coexists with an underlying structural lesion of motor pathways.
- Described with lesions in:
- Ventrolateral thalamus
- Motor cortex and parietal lobe
- Ipsilateral pons or medulla
- Midbrain asterixis:
- Segmental drop attack
Differential Diagnosis of Asterixis (negative myoclonus)
- Hepatic failure
- Renal failure
- Respiratory failure
- Acidotic states:
- Diabetic ketoacidosis
- Poisoning (large anion gap)
- Hyperosmolar states:
- Usually high blood sugar (1500–2000 mg%); non-ketotic diabetic ketoacidosis
- Hyperlipidemia
- Renal failure
Spinal Myoclonus
- General considerations:
- Definition:
- Repetitive myoclonic jerking of an extremity with flexor muscle predominance. Two basic types:
- Simple segmental myoclonus
- Propriospinal myoclonus
- Clinical features:
- Simple segmental myoclonus is repetitive myoclonic movements of one extremity that may be rhythmical and differ slightly in amplitude and frequency. The myoclonus involves one or more adjacent segments
Differential Diagnosis of Spinal Myoclonus
- Hyperosmolar state (non-ketotic diabetic ketoacidosis)
- HZ infection
- Trauma
- Paraneoplastic syndromes
- HIV
- Spinal arteriovenous malformation
- Arteriography of thoracic intercostal arteries
Propriospinal Myoclonus
- General considerations:
- Definition: rhythmic or arrhythmic spontaneous or rarely stimulus sensitive flexion or extension of the axial muscles. There may be spread to the extremities, but not to cranially innervated muscles.
- Neurophysiologic studies reveal:
- A characteristic pattern of order of recruitment. The myoclonic generators are mid thoracic segments which are followed by propagation up and down the spinal cord.
- Involved propriospinal fibers conduct at 3–11 meters/second
Differential Diagnosis of Propriospinal Myoclonus
- Tumor
- Demyelinating disease
- Infection
- Spinal anesthesia
- Alpha interferon therapy (renal cell carcinoma)
- Cervical hemangioblastoma
Palatal Myoclonus
- General considerations:
- Rhythmic contractions usually 60–180/minute of the palate and pharyngeal innervated musculature. The palatal muscle contractions may occur with synchronous rhythmic movements of the ocular muscles, diaphragm, head and neck.
- Persists in sleep
- Usually caused by lesions of Mollaret's triangle. These are projections between the red nucleus, inferior olive, and the dentate nucleus.
- Inferior olivary nucleus appears to be the generator
Differential Diagnosis of Palatal Myoclonus
- Rarely from cortical lesions
- Epilepsia partialis continua (similar)
- Vascular (vertebral artery)
- Traumatic
- Neoplastic
- Demyelinating
Rhythmic Palatal Myoclonus
- General considerations:
- Marked division into symptomatic and essential forms
- Symptomatic Palatal Myoclonus
- Clinical features:
- Onset fourth to sixth decade
- Males>females
- Frequency of 107–164 cycles/minute
- May present with ear click
- Does not cease with sleep
- Persists for life
- Extra palatal involvement
- Due to levator palatini contraction
- Pathology:
- Hypertrophied inferior olivary nucleus
- Cerebellar or brainstem disease (vascular most often)
Essential Rhythmic Palatal Myoclonus
- Clinical features:
- 26–420 cycle/minute
- Not associated with structural brainstem or cerebellar pathology
- Equal in males and females
- Onset second to fourth decades
- Presents with ear click (eustachian tube movement either when opposed or when breaking the surface tension when opening)
- Not associated with nystagmus or extremity tremor
- Remissions may occur
- May or may not remit during sleep
- Due to tensor veli palatini contractions
Oculopalatal Myoclonus
- General considerations:
- Oculopalatal myoclonus is often seen in conjunction with a vertical one and one half syndrome that involves the VIIth nerve:
- Lateral Variant:
- Jerky oblique, torsional and rotary nystagmoid components associated with lateral palatal myoclonus
- Midline variant:
- Vertical pendular eye movements (equal superior and inferior displacement without pause)
- Associated symmetrical bilateral palatal myoclonus
- Lingual Myoclonus:
- Occurs with Arnold Chiari malformations
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