1) The Electrophysiologic Phenomenon (certain electrical characteristics)
Positive Myoclonus: a contraction
of a group of muscles lasting < 300 milliseconds .
Negative Myoclonus (asterixis): a sudden relaxation of a group of muscles.
2) Classification by the Anatomical Origin Electrical Discharge
From the surface of the brain (Cortical Myoclonus).............Epileptic
From deeper within the brain (Subcortical Myoclonus)
From an electrical impulse within the spinal cord (Spinal or Segmental Myoclonus)
From an electrical impulse within a peripheral nerve (Peripheral Myoclonus eg. hemifacial spasm)
3) Classification by Body Parts Involved
Focal
If only one body part is affected
myoclonus is called "focal". (eg. myoclonic jerks of 1/2 the face ( "hemifacial spasm"), or when the eyes are affected ("Opsoclonus").
Segmental
If only one segment of the body is affected myoclonus is called "segmental" (eg. hiccoughs).
Multi-focal
If multiple areas body are
affected by myoclonus at different times it is called
"Multi-focal"(eg. poly-mini-myoclonusis a condition where very small myoclonic jerks occur in many different parts of the body in an almost continuous fashion).
Generalized
If the entire body is affected then myoclonus is called "Generalized". eg. a startle response.
4) Classification by Timing Pattern
Myoclonus can occur in a solitary
pattern ("isolated myoclonus"), in repetitive ("rhythmic myoclonus") patterns, just as one falls asleep ( "hypic jerks"), during sleep ("nocturnal
myoclonus") or can create circular ("oscillatory myoclonus" ) patterns of movement.
5) Classification by Myoclonic Triggers
Myoclonic jerks may be triggered
by a variety of stimuli ("stimulus sensitive myoclonus") including sound, touch, fright or startle, and flashes of light.
Frequently myoclonic jerks occur
during an active voluntary muscle contraction ("action myoclonus" eg after lack of oxygen to the brain ( "Post anoxic myoclonus").
6) Classification as to Cause
Physiologic Myoclonus
Myoclonus can occur as a normal
phenomenon. Types of normal ("physiologic") myoclonus include; hypic jerks (myoclonus as a person falls asleep), startle response, exercise or anxiety induced myoclonus, and
hiccoughs.
Primary Myoclonus
Primary myoclonic conditions are
conditions that result in myoclonus that are not secondary to some other medical problem. These primary forms of myoclonus can be inherited (eg. Essential Myoclonus), or idiopathic (no known
cause).
Secondary Myoclonus
There is a large number of varied
conditions that can cause myoclonus as a symptom. These include various types of seizures (epilepsy), inherited disorders of metabolism, disorders of brain fatty materials leading to excess
build up of these materials (Storage diseases (eg Lafora body disease), types of slowly progressive neurologic conditions that may or may not run in families (eg. spinocerebellar degenerations,
basal
ganglia degeneration, mitochondrial disorders), and other dementing illnesses (Jakob-Cruetzfeldt disease, Alzheimer's disease). Infectious diseases of a variety of types (eg. viral encephalitis, AIDS, syphilis, "mad cow" disease) can have myoclonus as part of their symptom complex. Lack of oxygen can result in damage to nerve cells and lead to myoclonus (post anoxic myoclonus). Local trauma, or other types of injury to the brain, spinal cord, or peripheral nerves can lead to focal myoclonic jerks.
