The Gale Encyclopedia of Neurological Disorders Vol 2 (M Z) pdf
The GALE
ENCYCLOPEDIA of
NEurological D isorders
VOLUME
M - Z
G L O S S A R Y
I N D E X
GALE
ENCYCLOPEDIA of
N Eurological
D isorders
S T A C E Y L . C H A M B E R L I N , B R I G H A M N A R I N S , E D I T O R S
Project Editors Stacey L. Chamberlin, Brigham Narins Editorial Erin Watts Editorial Support Services Andrea Lopeman Indexing Services Synapse
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[DNLM: 1. Nervous System Diseases—Encyclopedias—English. 2. Nervous System Diseases—Popular Works. WL 13 G151 2005] I. Title: Encyclopedia of neurological
disorders. II. Chamberlin, Stacey L. III. Narins, Brigham, 1962– IV. Gale Group.
RC334.G34 2005616.8'003—dc22 2004021644
CONTENTS
List of Entries ................................................vii
Introduction ..................................................xiii
Advisory Board..............................................xv
Contributors .................................................xvii
Entries Volume 1: A–L ........................................................1 Volume 2: M–Z ...................................................511Glossary .......................................................941
General Index...............................................973
A
B
❙
Congenital myasthenia Congenital myopathies Corpus callosotomy Corticobasal degeneration Craniosynostosis Craniotomy Creutzfeldt-Jakob disease CT scan Cushing syndrome Cytomegalic inclusion body disease
❙
Back pain Bassen-Kornzweig syndrome Batten disease Behçet disease Bell’s palsy Benign positional vertigo Benzodiazepines Beriberi Binswanger disease Biopsy Blepharospasm Bodywork therapies Botulinum toxin Botulism Brachial plexus injuries Brain anatomy Brain and spinal tumors Brown-Séquard syndrome
Abulia Acetazolamide Acupuncture Acute disseminated encephalomyelitis Adrenoleukodystrophy Affective disorders Agenesis of the corpus callosum Agnosia AIDS Alcohol-related neurological disease Alexander disease Alpers’ disease Alternating hemiplegia Alzheimer disease Amantadine Amnestic disorders Amyotrophic lateral sclerosis Anatomical nomenclature Anencephaly Aneurysms Angelman syndrome Angiography Anosmia Anticholinergics Anticonvulsants Antiepileptic drugs Antimigraine medications Antiparkinson drugs Antiviral drugs Anxiolytics Aphasia Apraxia Arachnoid cysts Arachnoiditis Arnold-Chiari malformation Arteriovenous malformations Aspartame Asperger’s disorder Assistive mobile devices Ataxia-telangiectasia Ataxia Atomoxetine Attention deficit hyperactivity disorder Autism Autonomic dysfunction
D
C
Central nervous system Central nervous system stimulants Central pain syndrome Cerebellum Cerebral angiitis Cerebral cavernous malformation Cerebral circulation Cerebral dominance Cerebral hematoma Cerebral palsy Channelopathies Charcot-Marie-Tooth disorder Cholinergic stimulants Cholinesterase inhibitors Chorea Chronic inflammatory demyelinating polyneuropathy Clinical trials
Dandy-Walker syndrome Deep brain stimulation Delirium Dementia Depression Dermatomyositis Devic syndrome Diabetic neuropathy disease Diadochokinetic rate Diazepam Dichloralphenazone Dichloralphenazone, Isometheptene, and Acetaminophen Diencephalon
Diet and nutrition Disc herniation Dizziness Dopamine receptor agonists Dysarthria Dysesthesias Dysgeusia Dyskinesia Dyslexia Dyspraxia Dystonia Electroencephalography Electromyography Empty sella syndrome Encephalitis and Meningitis Encephalitis lethargica Encephaloceles Encephalopathy Endovascular embolization Epidural hematoma Epilepsy Exercise
❙ E
Electric personal assistive mobility devices
Canavan disease Carbamazepine Carotid endarterectomy Carotid stenosis Carpal tunnel syndrome Catechol-O-methyltransferase inhibitors Central cord syndrome
❙
❙
J
N
❙
Machado-Joseph disease
Magnetic resonance imaging (MRI)
Megalencephaly Melodic intonation therapy Ménière’s disease Meninges Mental retardation Meralgia paresthetica Metachromatic leukodystrophy Microcephaly Mitochondrial myopathies Modafinil Moebius syndrome Monomelic amyotrophy Motor neuron diseases Movement disorders Moyamoya disease Mucopolysaccharidoses Multi-infarct dementia Multifocal motor neuropathyList of Entries
Pain Pallidotomy Pantothenate kinase-associated neurodegeneration Paramyotonia congenita Paraneoplastic syndromes Parkinson’s disease Paroxysmal hemicrania Parsonage-Turner syndrome Perineural cysts Periodic paralysis Peripheral nervous system Peripheral neuropathy Periventricular leukomalacia Phantom limb Pharmacotherapy Phenobarbital Pick disease Pinched nerve Piriformis syndrome Plexopathies Poliomyelitis
❙
Occipital neuralgia Olivopontocerebellar atrophy Opsoclonus myoclonus Organic voice tremor Orthostatic hypotension Oxazolindinediones
❙
Narcolepsy Nerve compression Nerve conduction study Neurofibromatosis Neuroleptic malignant syndrome Neurologist Neuromuscular blockers Neuronal migration disorders Neuropathologist Neuropsychological testing Neuropsychologist Neurosarcoidosis Neurotransmitters Niemann-Pick Disease
Fabry disease Facial synkinesis Fainting Fatigue Febrile seizures Felbamate Fisher syndrome Foot drop Fourth nerve palsy Friedreich ataxia
Multiple sclerosis Multiple system atrophy Muscular dystrophy Myasthenia, congenital Myasthenia gravis Myoclonus Myofibrillar myopathy Myopathy Myotonic dystrophy
❙
F
Gabapentin Gaucher disease Gene therapy Gerstmann-Straussler-Scheinker disease Gerstmann syndrome Glossopharyngeal neuralgia Glucocorticoids Guillain-Barré syndrome
❙
Kennedy’s disease Klippel Feil syndrome Krabbe disease Kuru
Joubert syndrome ❙
❙
K
L
G
❙
Lambert-Eaton myasthenic syndrome
Laminectomy Lamotrigine Learning disorders Lee Silverman voice treatment Leigh disease Lennox-Gastaut syndrome Lesch-Nyhan syndrome Leukodystrophy Levetiracetam Lewy body dementia Lidocaine patch Lissencephaly Locked-in syndrome Lupus Lyme diseaseO
P
H
❙
Hallucination Headache Hearing disorders Hemianopsia Hemifacial spasm Hereditary spastic paraplegia Holoprosencephaly HTLV-1 Associated Myelopathy Huntington disease Hydantoins Hydranencephaly Hydrocephalus Hydromyelia Hypersomnia Hypotonia Hypoxia
M
❙
I Idiopathic neuropathy Inclusion body myositis Incontinentia pigmenti Infantile spasms Inflammatory myopathy Interferons Polymyositis Pompe disease Porencephaly Positron emission tomography (PET) Post-polio Syndrome Primary lateral sclerosis Primidone Prion diseases Progressive multifocal leukoencephalopathy Progressive supranuclear palsy Pseudobulbar palsy Pseudotumor cerebri
❙
U
V Valproic acid and divalproex
R
❙
Radiation Radiculopathy Ramsay-Hunt syndrome type II Rasmussen’s encephalitis Reflex sympathetic dystrophy Refsum disease Repetitive motion disorders Respite Restless legs syndrome Rett syndrome Reye syndrome
T
W
Zellweger syndrome Zonisamide List of Entries
❙
Wallenberg syndrome West Nile virus infection Whiplash Whipple’s Disease Williams syndrome Wilson disease
❙
sodium Vasculitic neuropathy Vasculitis Ventilatory assistance devices Ventricular shunt Ventricular system Vertebrobasilar disease Vestibular schwannoma Visual disturbances Vitamin/nutritional deficiency Von Hippel-Lindau disease
Ulnar neuropathy Ultrasonography ❙
❙
Tremors Trigeminal neuralgia Tropical spastic paraparesis Tuberous sclerosis
Tabes dorsalis Tay-Sachs disease Temporal arteritis Temporal lobe epilepsy Tethered spinal cord syndrome Third nerve palsy Thoracic outlet syndrome Thyrotoxic myopathy Tiagabine Todd’s paralysis Topiramate Tourette syndrome Transient global amnesia Transient ischemic attack Transverse myelitis Traumatic brain injury
❙
Sixth nerve palsy Sjogren-Larsson Syndrome Sleep apnea Social workers Sodium oxybate Sotos syndrome Spasticity Speech synthesizer Spina bifida Spinal cord infarction Spinal cord injury Spinal muscular atrophy Spinocerebellar ataxia Status epilepticus Stiff person syndrome Striatonigral degeneration Stroke Sturge-Weber syndrome Stuttering Subacute sclerosing panencephalitis Subdural hematoma Succinamides Swallowing disorders Sydenham’s chorea Syringomyelia
S
Sandhoff disease Schilder’s disease Schizencephaly Schizophrenia Sciatic neuropathy Sciatica Seizures Septo-optic dysplasia Shaken baby syndrome Shingles Single Proton Emission Computed Tomography
❙
Z
PLEASE READ—IMPORTANT INFORMATION
The Gale Encyclopedia of Neurological Disorders is
a medical reference product designed to inform and edu- cate readers about a wide variety of diseases, syndromes, drugs, treatments, therapies, and diagnostic equipment. Thomson Gale believes the product to be comprehensive, but not necessarily definitive. It is intended to supplement, not replace, consultation with a physician or other health- care practitioner. While Thomson Gale has made sub- stantial efforts to provide information that is accurate, comprehensive, and up-to-date, Thomson Gale makes no representations or warranties of any kind, including with- out limitation, warranties of merchantability or fitness for a particular purpose, nor does it guarantee the accuracy, comprehensiveness, or timeliness of the information con- tained in this product. Readers are advised to seek profes- sional diagnosis and treatment for any medical condition, and to discuss information obtained from this book with their healthcare providers.
INTRODUCTION
The Gale Encyclopedia of Neurological Disorders(GEND) is a one-stop source for medical information that covers diseases, syndromes, drugs, treatments, therapies, and diagnostic equipment. It keeps medical jargon to a minimum, making it easier for the layperson to use. The
Gale Encyclopedia of Neurological Disorders presents au-
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Treatments
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Gale Encyclopedia of Neurological Disorders. Articles
follow a standardized format that provides information at a glance. Rubrics include:
Diseases
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as Hallervorden-Spatz disease that points to the entry en- The Gale Encyclopedia of Neurological Disorders titled Pantothenate kinase-associated neurodegeneration. has been designed with ready reference in mind:
oduction
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rect readers to where information on subjects without their own entries can be found. Cross-references are also used to The Gale Encyclopedia of Neurological Disorders is assist readers looking for information on diseases that are enhanced with over 100 images, including photos, tables, now known by other names; for example, there is a cross- and customized line drawings.
An advisory board made up of prominent individuals from the medical and healthcare communities provided invaluable assis-
tance in the formulation of this encyclopedia. They defined the scope of coverage and reviewed individual entries for accu-
racy and accessibility; in some cases they contributed entries themselves. We would therefore like to express our great
appreciation to them: Laurie Barclay, MD Brenda Wilmoth Lerner, RN Roy Sucholeiki, MD Neurologist and Writer Nurse, Writer, and Editor Professor, Director of theTampa, FL London, UK Comprehensive Epilepsy
Program
Department of Neurology
Pharmacist, Clinician, Writer, Associate Professor
Loyola University Health System
Editor, and Consultant Clinical Neurosciences
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Medicine Gil I. Wolfe, MD
Joel C. Kahane, PhD
Stanford, CA Associate Professor
Professor, Director of the
Department of Neurology
Anatomical Sciences Laboratory
The University of Texas The School of Audiology and
Southwestern Medical Center Speech-Language Pathology
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CONTRIBUTORS
Lisa Maria Andres, MS, CGC Certified Genetic Counselor and Medical WriterRobert G. Best, PhD Director
James Paul Dworkin, PhD
Professor
Bruno Verbeno Azevedo
Department of Embryology, Obstetrics, and Gynecology
Adam J. Cohen, MD Craniofacial Surgery, Eyelid and Facial Plastic Surgery,
Neuro-Ophthalmology
Downers Grove, IL
Tish Davidson, AM Medical Writer
Fremont, CA
Paul Arthur Science writer
Department of Otolaryngology, Voice/Speech Pathology Program and Laboratory
Wayne State University Detroit, MI
L. Fleming Fallon, Jr., MD, DrPH Professor
Department of Public Health Bowling Green State University Bowling Green, OH
Antonio Farina, MD, PhD
University of Bologna Bologna, Italy
Institute for Molecular and Human Genetics
Kevin Fitzgerald Science Writer and Journalist
South Windsor, CT
Paula Anne Ford-Martin Medical Writer
Warwick, RI
Lisa A. Fratt Medical Writer
Ashland, WI
Rebecca J. Frey, PhD Freelance Medical Writer
New Haven, CT
Sandra L. Friedrich, MA Science Writer
Clinical Psychology Chicago, IL
Sandra Galeotti, MS Science Writer
Sao Paulo, Brazil
Georgetown University Washington, D.C.
Bryan Richard Cobb, PhD
Espirito Santo University Vitória, Brazil
TCB Research Boalsburg, PA
Deepti Babu, MS, CGC Genetic Counselor
Marshfield Clinic Marshfield, WI
Laurie Barclay, MD Neurologist and writer
Tampa, FL
Julia Barrett Science Writer
Madison, WI
Danielle Barry, MS Graduate Assisstant
Center of Alcohol Studies Rutgers University Piscataway, NJ
Maria Basile, PhD Medical Writer
Roselle, NJ
Tanja Bekhuis, PhD Science Writer and Psychologist
Juli M. Berwald, PhD Geologist (Ocean Sciences)
Fairfax, VA
Chicago, Illinois
London, England
Division of Genetics University of South Carolina School of Medicine Columbia, SC
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San Francisco, CA
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Fairfield, PA
Francisco de Paula Careta
Espirito Santo University Vitória, Brazil
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Warren, MI
Michael Mooney, MA, CAC Consultant Psychotherapist
School of Medicine University of Rijeka Pula, Croatia
Igor Medica, MD, PhD Assistant Professor
Wayne State University Detroit, MI
Emergency Physician
Iuri Drumond Louro, MD, PhD Adjunct Professor
Human and Molecular Genetics Espirito Santo University Vitória, Brazil
Based Health Care University of Oxford Oxford, England
Foster City, CA
University of California, San Francisco
Department of Biomagnetic Imaging
Member: American Academy of Neurology, American Association of Electrodiagnostic Medicine
Peter T. Lin, MD
University of Queensland Brisbane, Australia
The Alfred Hospital Victoria, Australia Oxford’s Program in Evidence-
Marcos do Carmo Oyama
Agnieszka Maria Lichanska,
PhDJ. Ricker Polsdorfer, MD Medical Writer
Contributors
Clinipharm Services Seal Beach, CA
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Scott J. Polzin, MS, CGC Medical Writer
Phoenix, AZ
Baltimore, MD
Espirito Santo University Vitória, Brazil
University of Maryland School of Medicine
Division of Endocrinology, Diabetes, and Nutrition
Toni I. Pollin, MS, CGC
Division of Medical Genetics University Medical Center Lubiana, Slovenia
Borut Peterlin, MD, PhD Neurologist; Consultant Clinical Geneticist; Director
Espirito Santo University Vitória, Brazil
Greiciane Gaburro Paneto
Department of Microbiology and Parasitology
Science Policy Institute London, UK
Sharon, VT
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Cindy L. Hunter, CGC Genetic Counselor
Medical Genetics Department Indiana University School of
Medicine Indianapolis, IN
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Kelly Karpa, PhD, RPh Assistant Professor
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Genetic Counselor, Assistant Professor of NeurologyWayne State University Detroit, MI
Judy Leaver, MA
Behavioral Health Writer and
ConsultantWashington, D.C.
Adrienne Wilmoth Lerner
University of Tennessee College of Law
Knoxville, TN
Brenda Wilmoth Lerner, RN
Nurse, Writer, and EditorLondon, UK
Hannah M. Hoag, MSc Science and Medical Writer
Research Analyst
Geological Institute of the Russian Academy of Sciences
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Holly Ann Ishmael, MS, CGC Genetic Counselor
The Children’s Mercy Hospital Kansas City, MO
Joel C. Kahane, PhD Professor, Director of the Anatomical Sciences
Laboratory
The School of Audiology and Speech-Language Pathology
The University of Memphis Memphis, TN
Moscow, Russia
Robert Ramirez, DO Medical Student
Lancaster, PA
Department of Neurology Loyola University Health System Chicago, IL
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James Cancer Hospital, Ohio State University
Columbus, OH
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Roy Sucholeiki, MD Professor, Director of the Comprehensive Epilepsy
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Department of Neurology and Neurosciences
Stanford University Stanford, CA.
Bruno Marcos Verbeno
Espirito Santo University Vitória, Brazil
Beatriz Alves Vianna
Espirito Santo University Vitória, Brazil
Program
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Amie Stanley, MS Genetic Counselor
Medical Genetics The Cleveland Clinic Cleveland, OH
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Diagnostics
SUNY Upstate Medical University Syracuse, NY
Contributors
A M
❙Machado-Joseph disease Definition
Machado-Joseph disease (MJD), also known as spin- ocerebellar ataxia Type 3 (SCA 3), is a rare hereditary disorder affecting the central nervous system, especially the areas responsible for movement coordination of limbs, facial muscles, and eyes. The disease involves the slow and progressive degeneration of brain areas involved in motor coordination, such as the cerebellar, extrapyramidal, py- ramidal, and motor areas. Ultimately, MJD leads to paral- ysis or a crippling condition, although intellectual functions usually remain normal. Other names of MJD are Portuguese-Azorean disease, Joseph disease, Azorean disease.
Causes and symptoms
Description
Machado-Joseph disease was first described in 1972 among the descendants of Portuguese-Azorean immi- grants to the United States, including the family of William Machado. In spite of differences in symptoms and degrees of neurological degeneration and movement im- pairment among the affected individuals, it was suggested by investigators that in at least four studied families the same gene mutation was present. In early 1976, investi- gators went to the Azores Archipelago to study an existing neurodegenerative disease in the islands of Flores and São Miguel. In a group of 15 families, they found 40 people with neurological disorders with a variety of different symptoms among the affected individuals.
Another research team in 1976 reported an inherited neurological disorder of the motor system in Portuguese families, which they named Joseph disease. During the same year, the two groups of scientists both published in- dependent evidence suggesting that the same disease was the primary cause for the variety of symptoms observed. When additional reports from other countries and ethnic groups were associated with the same inherited disorder, it was initially thought that Portuguese-Azorean sailors had been the probable disseminators of MJD to other pop- ulations around the world during the sixteenth century pe- riod of Portuguese colonial explorations and commerce. Presently, MJD is found in Brazil, United States, Portugal, Macau, Finland, Canada, Mexico, Israel, Syria, Turkey, Angola, India, United Kingdom, Australia, Japan, and China. Because MJD continues to be diagnosed in a vari- ety of countries and ethnic groups, there are current doubts about its exclusive Portuguese-Azorean origin.
The gene responsible for MJD appears at chromo- some 14, and the first symptoms usually appear in early adolescence. Dystonia (spasticity or involuntary and repetitive movements) or gait ataxia is usually the initial symptoms in children. Gait ataxia is characterized by un- stable walk and standing, which slowly progresses with the appearance of some of the other symptoms, such as hand dysmetria, involuntary eye movements, loss of hand and superior limbs coordination, and facial dystonia (ab- normal muscle tone). Another characteristic of MJD is clinical anticipation, which means that in most families the onset of the disease occurs progressively earlier from one generation to the next. Among members of the same fam- ily, some patients may show a predominance of muscle tone disorders, others may present loss of coordination, some may have bulging eyes, and yet another sibling may be free of symptoms during his/her entire life. In the late stages of MJD, some people may experience delirium or dementia.
According to the affected brain area, MJD is classified as Type I, with extrapyramidal insufficiency; Type II, with cerebellar, pyramidal, and extrapyramidal insufficiency; and Type III, with cerebellar insufficiency. Extrapyramidal tracts are networks of uncrossed motor nerve fibers that function as relays between the motor areas and corre- sponding areas of the brain. The pyramidal tract consists of groups of crossed nerves located in the white matter of the spinal cord that conduct motor impulses originated in
Treatment
Autosomal Relating to any chromosome besides the X and Y sex chromosomes. Human cells con- tain 22 pairs of autosomes and one pair of sex chro- mosomes.
Cerebellar Involving the part of the brain (cere- bellum) that controls walking, balance, and coor- dination.
Mac hado-J oseph disease Key Terms
Clinical Trials
Fax: (312) 803-0138. dystonia@dystonia-foundation.org. <http://www.dystonia-foundation.org>.
ORGANIZATIONS Dystonia Medical Research Foundation. 1 East Wacker Drive, Suite 2430, Chicago, IL 60601-1905. (312) 755-0198;
Machado-Joseph Disease Fact Sheet. May 5, 2003 (June 7, 2004). <http://www.ninds.nih.gov/ health_and_medical/pubs/machado-joseph.htm>.
OTHER National Institute of Neurological Disorders and Stroke.
Fenichel, Gerald M. Clinical Pediatric Neurology: A Signs and Symptoms Approach, 4th ed. Philadelphia: W. B. Saunders Company, 2001.
The frequency with which such genetic mutations trigger the clinical onset of disease is known as pene- trance. Machado-Joseph disease presents a 94.5% pene- trance, which means that 94.5% of the mutation carriers will develop the symptoms during their lives, and less than 5% will remain free of symptoms. Because the intensity and range of symptoms are highly variable among the af- fected individuals, it is difficult to determine the progno- sis for a given individual. As MJD progresses slowly, most patients survive until middle age or older.
Further basic research is needed before clinical trials become a possibility for MJD. Ongoing genetic and mo- lecular research on the mechanisms involved in the genetic mutations responsible for the disease will eventually yield enough data to provide for future development and design of experimental gene therapies and drugs specific to treat those with MJD.
Other symptoms also require palliative treatment, such as muscle cramps, urinary disorders, and sleep problems.
Dysarthria, or difficulty to speak, and dysphagia, difficulty to swallow, can be treated with proper medication and speech therapy. Physical therapy can help patients with unsteady gait, and walkers and wheelchairs may be needed as the disease progresses.
Although there is no cure for Machado-Joseph dis- ease, some symptoms can be relieved, The medication Levodopa or L-dopa often succeeds in lessening muscle rigidity and tremors, and is often given in conjunction with the drug Carbidopa. However, as the disease pro- gresses and the number of neurons decreases, this pallia- tive (given for comfort) treatment becomes less effective. Antispasmodic drugs such as baclofen are also prescribed to reduce spasticity.
Diagnosis depends mainly on the clinical history of the family. Genetic screening for the specific mutation that causes MJD can be useful in cases of persons at risk or when the family history is not known or a person has symptoms that raise suspicion of MJD. Initial diagnosis may be difficult, as people present symptoms easily mis- taken for other neurological disorders such as Parkinson and Huntington diseases, or even multiple sclerosis.
Trinucleotide A sequence of three nucleotides. the opposite area of the brain to the arms and legs. Pyra- midal tract nerves regulate both voluntary and reflex mus- cle movements. However, as the disease progresses, both motor systems tracks will eventually suffer degeneration.
Phenotype The physical expression of an individ- ual’s genes. Spasticity Increased mucle tone, or stiffness, which leads to uncontrolled, awkward move- ments.
Penetrance The degree to which individuals pos- sessing a particular genetic mutation express the trait that this mutation causes. One hundred per- cent penetrance is expected to be observed in truly dominant traits.
Genotype The genetic makeup of an organism or a set of organisms. Mutation A permanent change in the genetic ma- terial that may alter a trait or characteristic of an in- dividual, or manifest as disease. This change can be transmitted to offspring.
Extrapyramidal Refers to brain structures located outside the pyramidal tracts of the central nervous system.
Dysarthria Slurred speech. Dystonia Painful involuntary muscle cramps or spasms.
Prognosis
Resources BOOKS
Diagnosis
Magnetic r esonance imaging (MRI)
Technician conducting an MRI. (Will & Deni McIntyre/Photo Researchers, Inc. Reproduced by permission.) International Machado-Joseph Disease Foundation, Inc. P.O.
Box 994268, Redding, CA 96099-4268. (530) 246-4722. MJD@ijdf.net. <http://www.ijdf.net>. National Ataxia Foundation (NAF). 2600 Fernbrook Lane, Suite 119, Minneapolis, MN 55447-4752. (763) 553-
0020; Fax: (763) 553-0167. naf@ataxia.org. <http://www.ataxia.org>. National Organization for Rare Disorders (NORD). P.O. Box 1968 (55 Kenosia Avenue), Danbury, CT 06813-1968.
(203) 744-0100 or (800) 999-NORD (6673); Fax: (203) 798-2291. orphan@rarediseases.org. <http://www. rarediseases.org>. Worldwide Education & Awareness for Movement Disorders (WE MOVE). 204 West 84th Street, New York, NY
10024. (212) 875-8312 or (800) 437-MOV2 (6682); Fax: (212) 875-8389. wemove@wemove.org. <http://www.wemove.org>.
Sandra Galeotti Macrencephaly see Megalencephaly Mad cow disease see Creutzfeldt-Jakob disease
Magnetic resonance imaging (MRI) Definition
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Magnetic resonance imaging (MRI) scanners rely on the principles of atomic nuclear-spin resonance. Using strong magnetic fields and radio waves, MRI collects and correlates deflections caused by atoms into images. MRIs (magnetic resonance imaging tests) offer relatively sharp pictures and allow physicians to see internal bodily struc- tures with great detail. Using MRI technology, physicians are increasingly able to make diagnosis of serious pathol- ogy (e.g., tumors) earlier, and earlier diagnosis often trans- lates to a more favorable outcome for the patient.
A varying (gradient) magnetic field exists in tissues in the body that can be used to produce an image of the tis- sue. The development of MRI was one of several powerful diagnostic imaging techniques that revolutionized medi- cine by allowing physicians to explore bodily structures and functions with a minimum of invasion to the patient.
In the last half of the twentieth century, dramatic ad- vances in computer technologies, especially the develop- ment of mathematical algorithms powerful enough to allow difficult equations to be solved quickly, allowed
MRI to develop into an important diagnostic clinical tool. In particular, the ability of computer programs to eliminate “noise” (unwanted data) from sensitive measurements en- hanced the development of accurate, accessible and rela- tively inexpensive noninvasive technologies.
Nuclear medicine is based upon the physics of excited atomic nuclei. Nuclear magnetic resonance (NMR) was one such early form of nuclear spectroscopy that eventu- ally found widespread use in clinical laboratory and med- ical imaging. Because a proton in a magnetic field has two quantized spin states, NMR allowed the determination of the complex structure of organic molecules and, ulti- mately, the generation of pictures representing the larger structures of molecules and compounds (such as neural tissue, muscles, organs, bones, etc.). These pictures were obtained as a result of measuring differences between the expected and actual numbers of photons absorbed by a tar- get tissue.
Description
Groups of nuclei brought into resonance, that is, nu- clei-absorbing and -emitting photons of similar electro- magnetic radiation (e.g., radio waves), make subtle yet distinguishable changes when the resonance is forced to change by altering the energy of impacting photons. The speed and extent of the resonance changes permit a non- destructive (because of the use of low energy photons) de- termination of anatomical structures. This form of NMR
Magnetic resonance imaging MRI An imaging technique used in evaluation and diagnoses of the brain and other parts of the body.
Megalencephal y
Resonance A condition in which the applied force (e.g., forced vibrations, forced magnetic field, etc.) becomes the same as the natural fre- quency of the target (e.g., tissue, cell structure, etc.). became the physical and chemical basis of the powerful diagnostic technique of MRI.
Resources PERIODICALS
A person with megalencephaly has a large, heavy brain. In general, a brain that weighs more than 1600 grams (about 3.5 pounds) is considered megalencephalic. The heaviest brain on record weighed 2850 grams (about 6.3 pounds). Macrocephaly, a related condition, refers to an abnormally large head. Macrocephaly may be due to megalencephaly or other causes such as hydrocephalus (an excess accumulation of fluid in the brain), and brain edema. Megalencephaly may be an isolated finding in an otherwise normal individual or it can occur in association with neurological problems (such as seizures or mental retardation) and/or somatic abnormalities (physical
Megalencephaly (also called macrencephaly) de- scribes an enlarged brain whose weight exceeds the mean (the average weight for that age and sex) by at least 2.5 standard deviations (a statistical measure of variation). Megalencephaly may also be defined in terms of volume rather than weight. Hemimegalencephaly (or unilateral megalencephaly) is a related condition in which brain en- largement occurs in one hemisphere (half) of the brain.
Paul Arthur ❙
AANLIB/home.html>.
<http://www.cis.rit.edu/htbooks/mri/>. Johnson, K. A., and J. A. Becker. The Whole Brain Atlas. May 9, 2004 (June 2, 2004). <http://www.med.harvard.edu/
WEBSITES Hornak, J. P. The Basics of MRI. May 9, 2004 (June 2, 2004).
Young, Emma. “Brain Scans Can Reveal Liars.” New Scientist (November 12, 2001).
After the September 11, 2001, terrorist attacks, a number of government agencies in the United States began to take a new look at brain scanning technology as a po- tential means of security screening. Such activity, along with an increase of interest in potential brain-wave scan- ning by the Federal Bureau of Investigation (FBI), has raised concerns among civil-liberties groups, which view brain-wave scanning as a particularly objectionable inva- sion of privacy.
In a 2001 University of Pennsylvania experiment using MRI, 18 subjects were given objects to hide in their pockets, then shown a series of pictures and asked to deny that the object depicted was in their pockets. Included was a picture of the object they had pocketed and so subjects were “lying” (making a deliberate false statement) if they claimed that the object was not in their pocket. An MRI recorded an increase of activity in the anterior cinglate, a portion of the brain associated with inhibition of responses and monitoring of errors, as well as the right superior frontal gyrus, which is involved in the process of paying attention to particular stimuli.
Studies of the potential of new brain wave scanners explore the possibility that MRI tests could be part of a more accurate form of polygraph (lie detector). Current polygraphs are of debatable accuracy (usually they are not admissible in court as evidence) and measure observable fluctuations in heart rate, breathing, perspiration, etc.
American chemist and physicist Paul Lauterbur and British physicist Sir Peter Mansfield shared the 2003 Nobel Prize in Physiology or Medicine for their discover- ies concerning the use of magnetic resonance to visualize different structures.
Healthy and diseased tissues produce different signal patterns and thus allow physicians to identify diseases and disorders.
The resolution of MRI scanning is so high that they can be used to observe the individual plaques in multiple sclerosis. In a clinical setting, a patient is exposed to short bursts of powerful magnetic fields and radio waves from electromagnets. MRI images do not utilize potentially harmful ionizing radiation generated by three-dimensional x-ray computed tomography (CT) scans, and there are no known harmful side effects. The magnetic and radio wave bursts stimulate signals from hydrogen atoms in the pa- tient’s tissues that, when subjected to computer analysis, create a cross-sectional image of internal structures and organs.