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$Unique_ID{BRK04031}
$Pretitle{}
$Title{Myoclonus, General}
$Subject{Myoclonus, General Rhythmical Myoclonus (Segmental Myoclonus,
including Nocturnal Myoclonus, Palatal Myoclonus and Respiratory Myoclonus)
Arrhythmic Myoclonus (Stimulus-Sensitive Myoclonus, including Pathologic
Myoclonus) Hereditary Essential Myoclonus (Paramyoclonus Multiple) Progressive
Myoclonic Epilepsy Ramsay Hunt Syndrome (Dyssynergia Cerebellaris Myoclonica)
Opsoclonus (Infantile Myoclonic Encephalopathy and Polymyoclonia) Familial
Arrhythmic Myoclonus Intention Myoclonus (Action Myoclonus, including
Postencephalitic Intention Myoclonus and Postanoxic Intention Myoclonus)
Tourette Syndrome Jumping Frenchmen of Maine Huntington's Disease Torsion
Dystonia Benign Essential Tremor}
$Volume{}
$Log{}

Copyright (C) 1986, 1987, 1988, 1990, 1991, 1992, 1993 National
Organization for Rare Disorders, Inc.

62:
Myoclonus, General

** IMPORTANT **
It is possible that the main title of the article (Myoclonus) is not the
name you expected.  Please check the SYNONYMS listing to find the alternate
name and disorder subdivisions covered by this article.

Synonyms

Disorder Subdivisions:

     Rhythmical Myoclonus (Segmental Myoclonus, including Nocturnal Myoclonus,
Palatal Myoclonus and Respiratory Myoclonus)
     Arrhythmic Myoclonus (Stimulus-Sensitive Myoclonus, including Pathologic
Myoclonus)
     Hereditary Essential Myoclonus (Paramyoclonus Multiple)
     Progressive Myoclonic Epilepsy
     Ramsay Hunt Syndrome (Dyssynergia Cerebellaris Myoclonica)
     Opsoclonus (Infantile Myoclonic Encephalopathy and Polymyoclonia)
     Familial Arrhythmic Myoclonus
     Intention Myoclonus (Action Myoclonus, including Postencephalitic
Intention Myoclonus and Postanoxic Intention Myoclonus)

Information on the following diseases can be found in the Related
Disorders section of this report:

     Tourette Syndrome
     Jumping Frenchmen of Maine
     Huntington's Disease
     Torsion Dystonia
     Benign Essential Tremor

General Discussion

** REMINDER **
The Information contained in the Rare Disease Database is provided for
educational purposes only.  It should not be used for diagnostic or treatment
purposes.  If you wish to obtain more information about this disorder, please
contact your personal physician and/or the agencies listed in the "Resources"
section of this report.


Myoclonus is a neurological movement disorder characterized by sudden,
involuntary contractions of skeletal muscles.  Based on the various symptoms,
there are three types of Myoclonus:  Intention Myoclonus, Rhythmical
Myoclonus, and Arrhythmic Myoclonus.

Intention Myoclonus (Action Myoclonus) includes Postanoxic Myoclonus and
Postencephalitic Myoclonus.

Arrhythmic Myoclonus (stimulus-sensitive myoclonus) includes:
Hereditary Essential Myoclonus (paramyoclonus multiplex), Hyperexplexia
(Essential Startle Disease), Opsoclonus (Infantile Myoclonic Encephalopathy,
Polymyoclonia Familial Arrhythmic Myoclonus), Progressive Myoclonic Epilepsy,
Ramsay Hunt Syndrome (Dyssynergia Cerebellaris Myoclonia).

Rhythmical Myoclonus includes (Segmental Myoclonus), Nocturnal Myoclonus,
Palatal Myoclonus, and Respiratory Myoclonus.

Symptoms

Intention Myoclonus is characterized by episodes of sudden, involuntary
muscle contractions that are triggered by voluntary movements, such as a
purposeful action.

In Arrhythmic Myoclonus, the muscle jerks lack any particular rhythm
(arrhythmic) and occur without warning.  The jerking movements may be
confined to a single muscle or involve all of the skeletal muscles.  The
severity of the muscle contractions may vary from episode to episode and may
differ among patients.  The jerking contractions may be very severe and
involve both sides of the body at the same time.  Muscle contractions may be
brought on (stimulated) by something that the person sees (visual), hears
(auditory), and/or touches (tactile).  The stimulus may also be physical
fatigue, stress, and/or anxiety.  In women, Myoclonus is often more intense
prior to the beginning of the menstrual flow (premenstrually).

Hyperexplexia (Essential Startle Response) is a form of Arrhythmic
Myoclonus characterized by an exaggerated muscular response to sudden loud
noises or other stimulus (startle reaction).  The muscle jerks of
Hyperexplexia come and go.  Opsoclonus is a form of Myoclonus that is limited
to one area of the body (localized).  Typically Opsoclonus affects the eyes
which jerk irregularly and together.  When Opsoclonus occurs in infants with
generalized Myoclonus, the infant is said to have Infantile Myoclonic
Encephalopathy or Polymyoclonia Familial.  Progressive Myoclonic Epilepsy,
which is potentially disabling, combines severe epilepsy with significant
stimulus-sensitive Myoclonus.  In advanced disease, dementia may appear.
(For more information, choose "Hyperexplexia" as your search term in the Rare
Disease Database.)

Ramsay Hunt Syndrome comprises many disorders including epilepsy,
myoclonus, and degeneration of part of the brain (cerebellum) and spinal
cord.  Other neurological impairments may also be present.  (For more
information, choose "Epilepsy" as your search term in the Rare Disease
Database.)

Rhythmical (segmental) Myoclonus has a distinctive symptom; the muscles
jerk at a frequency of 10 to 180 jerks per minute.  The affected muscles are
generally those that get their nerve supply (innervated) from one or more of
the spinal cord segments.  Unlike Arrhythmic Myoclonus, Rhythmical Myoclonus
is not relieved by sleep and is not triggered by sudden stimuli or voluntary
movements.

In Nocturnal Myoclonus (Restless Legs Syndrome) there is frequent jerking
of the body and/or the extremities, particularly the legs.  The legs may jerk
2 to 3 times a minute when falling asleep, sleeping, or during deep
relaxation during the day.  Insomnia frequently accompanies attacks of
Nocturnal Myoclonus.  (For more information about Nocturnal Myoclonus, choose
"Restless Legs" as your search term in the Rare Disease Database.)

In Palatal Myoclonus there are quick rhythmical contractions of a section
of the roof of the mouth (soft palate).  Sometimes other muscles contract
including those of the throat (pharynx), voice box (larynx), eyes, face,
and/or diaphragm.  Respiratory Myoclonus causes rapid rhythmic contractions
of the muscles of the diaphragm.  This may lead to shortness of breath or
difficulty breathing (dyspnea).

Causes

Several types of Arrhythmic Myoclonus are inherited.  Hereditary Essential
Myoclonus and Ramsay Hunt Syndrome are inherited as an autosomal dominant
genetic trait.  Human traits, including the classic genetic diseases, are the
product of the interaction of two genes, one received from the father and one
from the mother.  In dominant disorders a single copy of the disease gene
(received from either the mother or father) will be expressed "dominating"
the other normal gene and resulting in the appearance of the disease.  The
risk of transmitting the disorder from affected parent to offspring is fifty
percent for each pregnancy regardless of the sex of the resulting child.

Progressive Myoclonic Epilepsy, whether alone or with another hereditary
disease such as Tay-Sachs or Kufs Disease, is usually inherited as an
autosomal recessive genetic trait.  In recessive disorders, the condition
does not appear unless a person inherits the same defective gene for the same
trait from each parent.  If one receives one normal gene and one gene for the
disease, the person will be a carrier for the disease, but usually will not
show symptoms.  The risk of transmitting the disease to the children of a
couple, both of whom are carriers for a recessive disorder, is twenty-five
percent.  Fifty percent of their children will be carriers, but healthy as
described above.  Twenty-five percent of their children will receive both
normal genes, one from each parent, and will be genetically normal.

It is also possible that there is an X-linked form of Progressive
Myoclonus Epilepsy.  X-linked recessive disorders are conditions that are
coded on the X chromosome.  Females have two X chromosomes, but males have
one X chromosome and one Y chromosome.  Therefore, in females, disease traits
on the X chromosome can be masked by the normal gene on the other X
chromosome.  Since males only have one X chromosome, if they inherit a gene
for a disease present on the X, it will be expressed.  Men with X-linked
disorders transmit the gene to all their daughters, who are carriers, but
never to their sons.  Women who are carriers of an X-linked disorder have a
fifty percent risk of transmitting the carrier condition to their daughters,
and a fifty percent risk of transmitting the disease to their sons.

It is thought that in the majority of people with Myoclonus, symptoms
develop due to abnormally high levels of electrical discharges along nerve
cells.  In Rhythmical or Segmental Myoclonus, local trauma to the nerves in
the spinal cord that control muscles is usually responsible.  Overactivity of
certain areas within the brain (medullary reticular formation or cerebral
cortex) causes Arrhythmic Myoclonus.  Some types of Intention Myoclonus,
Essential Myoclonus, and Progressive Myoclonus Epilepsy may be associated
with decreased activity of serotonin, a chemical (neurotransmitter) in the
brain.

Viral infections, blood vessel disorders, benign growths, malignant
tumors, and/or traumatic lesions to the central nervous system may precede
either Rhythmical or Arrhythmic Myoclonus.  A lack of oxygen to the brain,
usually due to heart or respiratory failure, can cause Postanoxic Myoclonus.
Certain toxins, including some drugs in high doses, and metabolic disorders
have also been implicated as a cause of Myoclonus.

Affected Population

Myoclonus affects males and females in equal numbers.  Some forms of
Myoclonus are common and some forms are rare.

Related Disorders

Symptoms of the following disorders can be similar to those of Myoclonus.
Comparisons may be useful for a differential diagnosis:

Tourette Syndrome is a neurologic movement disorder that is characterized
by repetitive motor and vocal tics.  The first symptoms are usually rapid eye
blinking or facial grimaces.  Symptoms may also include facial tics and
involuntary movements of the extremities, shoulders, and the voluntary
muscles.  Inarticulate sounds or sometimes inappropriate words may occur.
Tourette Syndrome is not a progressive or degenerative disorder; rather,
symptoms tend to be variable and follow a chronic waxing and waning course.
Symptoms usually begin before the age of 16 years.  (For more information on
this disorder, choose "Tourette" as your search term in the Rare Disease
Database).

Jumping Frenchmen of Maine is a very rare disorder characterized by an
extreme startle response.  The symptoms occur as a response to sudden,
unexpected noise or movement.  The extreme startle reaction includes jumping,
raising the arms, hitting, yelling, unintelligible speech, and/or imitation
or repetition of another person's body movements (echopraxia).  The intensity
of the response increases with fatigue and stress.  (For more information on
this disorder, choose "Jumping Frenchmen of Maine" as your search term in the
Rare Disease Database.)

Huntington's Disease (Huntington's Chorea) is a rare inherited,
progressively degenerative neurological disorder characterized by involuntary
muscle movements and dementia.  Initially there are personality changes and
uncontrolled rapid jerky muscle movements.  In time, speech and memory become
impaired and involuntary muscle movements become more frequent and severe.
As Huntington's Disease progresses there is a further loss of cognitive
abilities and dementia.  The symptoms of this disorder usually begin during
adulthood, generally after the age of forty.  (For more information on this
disorder choose, "Huntington's" as your search term in the Rare Disease
Database.)

Torsion Dystonia is a rare inherited neurological disorder characterized
by involuntary contortions of the muscles in the neck, torso, arms, and legs.
Occasionally only one or a few muscles are involved.  People with Torsion
Dystonia typically have an awkward, sideways gait.  Other symptoms may
include foot drag, cramps on the hands and feet, difficulty in grasping
objects, and unclear speech.  The involuntary movements of Dystonia are slow
writhing movements.  (For more information on this disorder, choose "Torsion
Dystonia" as your search term in the Rare Disease Database.)

Benign Essential Tremor is a rare neurological disorder characterized by
a rhythmical tremor that may be pronounced.  This disorder typically affects
the upper extremities and the tremors usually has a frequency of 4 to 12
times per second.  The tremors may be aggravated by stress, anxiety, fatigue,
and/or cold temperatures.  Relief from the tremors may be achieved by rest
and sedation.  The symptoms of Benign Essential Tremor generally stabilize
after a period of progression.  (For more information on this disorder,
choose "Benign Essential Tremor" as your search term in the Rare Disease
Database.)

Therapies:  Standard

Clonazepam and other drugs known as benzodiazepine derivatives are commonly
used to treat most forms of Myoclonus.  These include Arrhythmic Myoclonus,
including Progressive Myoclonus Epilepsy, Ramsay Hunt Syndrome, Myoclonus
associated with Idiopathic Epilepsy, Infantile Spasms, and Postencephalitic
and Postanoxic Intention Myoclonus.  The drug diazepam is also used to treat
these types of Myoclonus.  People with this disorder may become tolerant to
these drugs after a course of several months.  Side effects such as
sleepiness, unsteady gait (ataxia), lethargy, and/or behavioral changes may
occur.

Other anticonvulsant drugs with antimyoclonic activity may also be useful
in the treatment of Myoclonus.  Valproic acid is the most effective drug in
the long-term treatment of Progressive Myoclonus Epilepsy; it is less
effective in other forms of Myoclonus.

ACTH or prednisone may be effective in treating a few forms of Myoclonus.
These include Infantile Spasms, Infantile Myoclonic Encephalopathy, and
Opsoclonus that occurs along with a brain tumor (neuroblastoma).

Rhythmical Myoclonus is more difficult to treat.  Drugs that have shown
some promising results in some patients include clonazepam, tetrabenazine,
and haloperidol.

Genetic counseling will be of benefit for patients with the inherited
forms of Myoclonus and their families.

Therapies:  Investigational

An experimental drug, L-5 hydroxytryptophan (L-5HTP), is being studied for
use in the treatment of Myoclonus.  This drug is chemically similar to the
organic chemicals that form serotonin.  L-5HTP is used in combination with
the drug carbidopa.  The combination treatment is being investigated for its
use in the treatment of Postanoxic Intention Myoclonus, Progressive
Myoclonus Epilepsy, Essential Myoclonus, and Palatal Myoclonus.  The side
effects of this treatment mainly affect the gastrointestinal tract and may
include diarrhea and nausea.  These may be minimized by carefully managing
the amount of carbidopa that is given.  Combinations of clonazepam, valproic
acid, and L-5HTP with carbidopa may be the treatment of choice in some
patients with Myoclonus.  L-5HTP is being developed by:

     Circa Pharmaceuticals
     130 Lincoln St.
     Copiague, NY  11726

The drug Acetazolamide is being studied as a treatment for people with
Ramsay Hunt Syndrome and severe Action Myoclonus.  This drug is used in
combination with clonazepam, sodium valproate, primidone and piracetam.  The
addition of acteazolamide to this combination may reduce the severity of
muscle contractions in some patients.  The long-term safety and effectiveness
of this treatment is under study.

Piracetam (Nootripil) is a drug that has been approved in England for
treatment of cortical Myoclonus.  This drug is used in combination with other
epilepsy drugs.  More study is needed to determine the long-term safety and
effectiveness of piracetam as a treatment for Myoclonus.

This disease entry is based upon medical information available through
April 1993.  Since NORD's resources are limited, it is not possible to keep
every entry in the Rare Disease Database completely current and accurate.
Please check with the agencies listed in the Resources section for the most
current information about this disorder.

Resources

For more information on Myoclonus, please contact:

     National Organization for Rare Disorders (NORD)
     P.O. Box 8923
     New Fairfield, CT  06812-1783
     [phone]

     National Pediatric Myoclonus Center
     Dept. of Neurology
     Children's Hospital
     111 Michigan Ave., NW
     Washington, DC  20010-2970

     Myoclonus Research Foundation
     200 Old Palisade Avenue, Suite 17D
     Fort Lee, NJ 07024
     [phone]

     NIH/National Institute of Neurological Disorders & Stroke (NINDS)
     9000 Rockville Pike
     Bethesda, MD  20892
     [phone]
     [phone]

     Epilepsy Foundation of America
     4351 Garden City Dr.
     Landover, MD  20785
     [phone]
     [phone]

For Genetic Information and Genetic Counseling Referrals:

     March of Dimes Birth Defects Foundation
     1275 Mamaroneck Avenue
     White Plains, NY 10605
     [phone]

     Alliance of Genetic Support Groups
     35 Wisconsin Circle, Suite 440
     Chevy Chase, MD  20815
     [phone]
     (800) 336-GENE

References

MENDELIAN INHERITANCE IN MAN, 10th Ed.:  Victor A. McKusick, Editor:  Johns
Hopkins University Press, 1992.  Pp. 737, 1574, 1928.

CECIL TEXTBOOK OF MEDICINE, 19th Ed.:  James B. Wyngaarden, and Lloyd H.
Smith, Jr., Editors; W.B. Saunders Co., 1990.  Pp. 2136-2137.

THE MERCK MANUAL, 16th Ed.:  Robert Berkow Ed.; Merck Research
Laboratories, 1992.  P. 1492.

PRINCIPLES OF NEUROLOGY, 4th Ed.; Raymond D. Adams, M.D. and Maurice
Victor, M.D., Editors; McGraw-Hill Information Services Company, 1989.  Pp.
269, 311, 808-811.

MYOCLONUS.  WHAT CAUSES IT, WHAT CONTROLS IT.  Van Woert, M.H., Chung
Hwang, E.; Consultant (April 1982).  Pp. 263-273.

TREATMENT OF MYOCLONUS, Van Woert, M.H., Chung Hwang, E.; Current Status
of Modern Therapy, vol. 8., ed. A. Barbeau.  MTP Press:  Lancaster, England,
1980.

HANDBOOK OF CLINICAL NEUROLOGY, Vol. 38;  Vinken, P.J. and Bruyn, G.W.
Ed.; North Holland Publishing Co., (Van Woert, M.H., Chung Hwang, E.)
Myoclonus Pages 575-93.

EFFECT OF ANTIEPILEPTIC AND ANTIMYOCLONIC DRUGS ON SEROTONIN RECEPTORS IN
VITRO.  M. R. Pranzatelli.  Epilepsia (Jul-Aug 1988; issue 29 (4)).  Pp. 412-
419.

THE TREATMENT OF SEVERE ACTION MYOCLONUS.  J. A. Obeso, et al.; Brain
(Jun 1989; issue 112 (Pt 3)).  Pp. 765-777.

ACETAZOLAMIDE IMPROVES ACTION MYOCLONUS IN RAMSEY HUNT SYNDROME.
L. Vaamonde et al., Clin Neuropharmacol (Oct 1992; 15(5)).  Pp. 392-396.