Definitions Used In HD
"C" through "D"


"A" through "B"
"C" through "D"
"E" through "J"
"K" through "P"
"Q" through "X"
Color coding:
Other diseases similiar to HD
 CT or CAT Scan:
The computed tomographic scan (also called a CT or CAT scan) uses an x-ray beam and a computer to generate 2 dimensional images of the body. The information is displayed in a cross-section or "slice" of body tissue. Neurological CT scans focus on the head or spine.

Carbonic anhydrase inhibitors: A class of medications that inhibits activity of the enzyme carbonic anhydrase.  Carbonic anhydrase activity serves to accelerate the transfer of carbon dioxide from tissue to the blood and on to the lungs. By restricting carbonic anhydrase activity, these agents decrease hydrogen ion concentrations in the renal tubules, increasing excretion of sodium, potassium, bicarbonate, and water.
Certain carbonic anhydrase inhibitors are prescribed to promote urinary production and excretion (i.e., as diuretics) or to lower fluid pressure within the eyes for those with glaucoma. They are also used to treat other conditions including epilepsy or certain neurologic movement disorders

Carnitine: A natural substance found in skeletal and cardiac muscle and the liver. Carnitine serves to transport fatty acids across mitochondrial membranes, thereby playing an important role in energy production and the metabolism of fatty acids.

Caudate nucle: One of the 3 major substructures that, together with the globus pallidus and putamen, form the basal ganglia. The caudate nuclei and putamen, which are relatively similar structurally and functionally, are collectively known as the striatum. Specialized clusters of nerve cells or nuclei within the caudate receive input from certain regions of the cerebral cortex. This information is processed and then relayed (by way of the thalamus) to areas of the brain responsible for controlling complex motor functions.
The caudate nuclei are specifically thought to process and transmit cognitive information that influences the initiation of complex motor activities.

cataplexy: A symptom characterized by the sudden loss of postural tone, often resulting in the individual falling to the floor. Cataplexy is often part of the narcolepsy complex.

Central nervous system (CNS): The brain and spinal cord. The CNS, which receives sensory impulses from and sends motor impulses to the peripheral nervous system (i.e., nerves outside the CNS), plays an essential role in the coordination and control of the entire body.

Central oscillators: nerve cells that discharge signals that result in alternating fluctuations of electrical impulses along certain tracts of the central
nervous system.

Cerebellum: A two-lobed region of the brain located behind the brainstem. The cerebellum receives messages concerning balance, posture, muscle tone, and muscle contraction or extension.
Working in coordination with the basal ganglia and thalamus, the cerebellum integrates, adjusts, and refines messages transmitted to muscle groups from the cerebral cortex (i.e., motor cortex). Thus, the cerebellum plays an essential role in producing smooth, coordinated voluntary movements; maintaining proper posture; and sustaining balance.

Cerebral cortex: The outer region of the brain's cerebral hemispheres. Comprised of gray matter, the cerebral cortex contains several deep folds (gyri) and grooves (sulci or fissures). Two sulci divide the surfaces of both cerebral hemispheres into four distinct lobes that are named for overlying bones of
the skull. These include the frontal,
temporal, occipital, and parietal lobes. The cerebral hemispheres are joined by a thick band of nerve fibers known as the corpus callosum.
The cerebral cortex is responsible for integrating higher mental functioning and conscious thought, sensations, and general

Cerebrospinal fluid (CSF): The fluid that flows through and protects the 4 cavities (ventricles) of the brain, the spinal cord's central canal, and the space (known as the subarachnoid space) between the middle and inner layers of the membrane (meninges) enclosing the brain and spinal cord.
Laboratory analysis of CSF, usually obtained via lumbar puncture, may help to diagnose central nervous system infections, certain tumors, or particular neurologic disorders. During lumbar puncture, CSF is removed from the spinal canal via a hollow needle inserted between certain bones of the spinal column within the lower back (i.e., usually the third and fourth lumbar vertebrae).

Chemodenervation: Interruption of a nerve impulse pathway via administration of a chemical substance, such as botulinum toxin (BTX). For example, intramuscular injections of BTX produce local relaxation of treated muscles by inhibiting the release of acetylcholine, a neurotransmitter that is present at the junctions of nerve and muscle cells and that regulates the delivery of messages from neurons to muscle fibers.

Chorea: Chorea, which means dance-like, is a movement that flows from joint to joint. In mild cases, the patient can cover these movements by incorporating them into other movements such as raising the hand to the head to brush ones hair or by sitting on ones hands.
Chorea may affect the face (grimaces, tongue protrusion, chewing), neck and trunk (swaying), limbs (restlessness), posture (motor impersistence), or gait (halting or lurching). An intermittently relaxing and tightening grip (milkmaid grasp) is one example of motor impersistence.
Chorea may be more prominent during action, stress, or other emotions. Like myoclonus, the list of causes of chorea is extensive, but it is useful to differentiate between primary hereditary conditions and secondary ones, commonly infrections and drug reactions.
Although one of the best known choreatic disorders is Huntington chorea, chorea is rare in the childhood-onset form (Westphal or akinetic rigid variant), but dementia and seizures are typical. Chorea is one of the significant manifestations of rheumatic fever.
Is worsened by stress, anxiety, or depression, is decreased during sleep, and often varies with posture or positioning. Various assistive devices maybe helpful. These include padded, reclining chairs, padding for the bed, andwrist and ankle weights to reduce the amplitude of the chorea.
Pharmacologic (drugs) treatment of chorea may worsen other aspects of the movement disorder, cognition or mood. Is the chorea severe enough to interfere with
voluntary activities such as writing, cooking, or eating? Does severe chorea
seem to be causing falls or accidents? Is highly visible chorea a significant source of distress for the patient?

Central nervous system: Refers to the brain and the spinal cord. 

Cerebrospinal fluid: The fluid that surrounds the brain and the spinal cord
Chorionic villus sampling (CVS):
A screening and diagnostic procedure performed during which tissue samples are obtained from a portion of the placenta using a specially guided needle via ultrasound. The placenta is the organ attached to the lining of the uterus that links the blood supplies of the developing fetus and the mother. The tissue sample is obtained from the layer from which the chorionic villi develop. Blood from the fetus flows through the umbilical cord
to the placenta and enters minute blood vessels arranged in multiple "thread-like" projections or chorionic villi surrounded by maternal blood.
Tissue samples obtained during chorionic villus sampling are analyzed to detect certain genetic or chromosomal abnormalities.

Chromosomes: The thread-like structures within the nuclei of cells comprised of DNA. Deoxyribonucleic acid or DNA carries genetic information involved in directing cellular activities, thus controlling bodily growth and functioning and determining the expression of inherited traits. The chromosomes contain thousands of hereditary units known as genes or segments of DNA molecules.

CLONUS:   An abnormal movement characterized by rapid contraction and relaxation of muscles. Brisk increase in tone with involuntary movements that result in dysfunction of the corticospinal tracts.
Clonus is frequently observed in conditions such as spasticity and certain seizure disorders.
Confabulation (fabricating answers)
Patients with severe frontal lobe lesions tend to fabricate quick, impulsive answers to questions. Some responses may be quite fanciful and imaginative. The patient cannot inhibit a response in order to check its validity. For example, when asked, "How did you get to the hospital?", the patient may respond with an imaginative tale that has very little relationship to the truth.This tendency to fabricate an answer is called confabulation.

It is most common among patients with basal forebrain lesions and among patients with additional impairment of memory ability.

Computerized tomography (CT) imaging or scanning: An advanced diagnostic scanning technique during which cross-sectional images of tissues and organs are produced by passing x-rays through the body at various angles. In some cases, a contrast medium, which is opaque on x-rays, may be injected intravenously to produce enhanced images of certain tissues, organs, or blood vessels

Congenital: Existing at birth.

Contractures:  Fixed resistance to passive stretching of certain muscles due to shortening or wasting (atrophy) of muscle fibers or the development of scar
tissue (fibrosis) over joints.

Contralateral: the opposite side. For example, during brain surgery for essential tremor, if the surgery is performed on the right side of the brain, the left side
of the body will be affected.
Corticobasal degeneration (CBD): A slowly progressive disorder characterized by neurodegenerative changes of certain brain regions, including the cerebral cortex (particularly the frontal and parietal lobes) and parts of the basal ganglia.
Most patients initially develop symptoms in their 60s or 70s. Primary findings may include stiffness (rigidity); slowness of movement (bradykinesia); loss of the ability to coordinate and execute certain purposeful movements of the arms or legs (limb apraxia); the sensation that a limb is not one's own ("alien limb phenomenon"); and other sensory abnormalities.
Affected individuals may also develop slurred, labored speech (dysarthria); dystonia; and irregular, involuntary, "shock-like" contractions of certain muscle groups, particularly of the hands and forearms, that may be provoked or aggravated by voluntary movement and certain external stimuli (action and reflex myoclonus) corticospinal tract: The nervous system structures that begin in the brain
and travel to the motor neuron cell to innervate the motor nerves. Referring to or connecting the outer region of the brain (cerebral cortex) and the spinal cord.
Cranial: Of or from the cranium or skull.

Cranial nerve nuclei: Specialized groups of nerve cells (nuclei) that give rise to and convey or receive impulses from sensory and motor constituents of the cranial nerves, which are the 12 pairs of nerves that emerge from the brain.
These nerve pairs convey sensory impulses for various functions including taste, smell, hearing, and vision; motor impulses involved in controlling eye movements, chewing, swallowing, facial expressions, etc.; and impulses for transmission to certain organs and glands for regulation of various involuntary or autonomic activities.

Cranial neuropathy: Disease or damage of a cranial nerve or nerves. The cranial nerves are the 12 nerve pairs that arise directly from the brain and are involved in conveying impulses for various functions including smell, hearing, vision, and taste; pupil contraction; eye movements; facial expressions; movements of the tongue, head, and shoulders; etc.
Cranial neuropathy may result in associated muscle weakness; abnormal sensations, such as numbness, tingling, or pain; or other findings. Specific symptoms
depend upon the specific nerve(s) affected.

Creutzfeldt-Jakob disease (CJD):
A rare, degenerative, life-threatening brain disorder characterized by severe, progressive dementia; visual disturbances; muscle weakness; and abnormal involuntary movements, such as sudden, brief, "shock-like" muscle spasms (myoclonus), tremor, and relatively slow writhing motions that appear to flow into one another (athetosis). Although CJD usually appears to occur sporadically, about 10 percent of cases are familial, potentially suggesting a hereditary predisposition to the disease.
Deep brain stimulation (DBS) is used for treatment of a movement disorder, during the procedure a recording electrode is often first used to determine exactly where to place the stimulation electrode. The recording electrode can measure the electrical activity in the brain directly.

deep tendon reflexes: The deep muscle stretch reflexes that are obtained by tapping on the tendons (such as the "knee jerk").

Degenerative: Marked by or pertaining to deterioration; particularly, deterioration of the function or structure of tissue or changes from a higher to a lower or less functionally active form.

Dementia An acquired loss of cognitive function that may affect language, attention, memory, personality and abstract reasoning. Dementia is a condition of impairment of memory, intellect, personality, and insight resulting from brain injury or disease. Some forms of dementia are progressive, such as Alzheimer's disease, Picks disease, or some forms of Parkinson's disease.
Language impairments are more or less prominent in different forms of dementia, but these are usually overshadowed by more widespread intellectual loss. Since dementia is so often a progressive disorder, the prognosis is quite different from aphasia.

Dendrites: The relatively narrow, branching projections that extend from the cell bodies of neurons. Nerve cells may contain multiple dendrites, which are stimulated by neurotransmitters, receive impulses from the nerve fibers (axons) of other neurons, and convey them toward their nerve cell bodies.

Dentatorubropallidoluysian atrophy: A rare genetic disorder that is most commonly described in Japan. Associated symptoms may become apparent in adolescence or adulthood.
Early-onset disease may be characterized by rapidly progressive neurodegenerative changes, including seizures, cognitive impairment, and brief, "shock-like" muscle spasms of certain muscles or muscle groups (myoclonus). Late-onset disease may be associated with progressively impaired control of voluntary movement (ataxia) and symptoms often seen in Huntington's disease (HD), including chorea and gradual loss of thought processing and acquired intellectual abilities (dementia).
Brain imaging studies typically reveal degenerative changes of the globus pallidus and specialized nerve cell clusters within the cerebellum (dentate nucleus).
Similar to HD, the disorder may result from abnormally long sequences or "repeats" of particular coded instructions (unstable expanded CAG repeats)
within a gene (located on chromosome 12).

Diaphragm: The dome-shaped muscle that separates the chest and abdomen. The diaphragm plays an essential role in breathing, contracting when air is
drawn into the lungs and relaxing upon exhalation.

Differential diagnosis: Distinguishing between two or more diseases and conditions with similar symptoms by systematically comparing and contrasting their clinical findings, including physical signs, symptoms, as well as the results of laboratory tests and other appropriate diagnostic procedures.

DNA:  deoxyribonucleic acid; a two-stranded molecule that contain the genes that provide the blueprint for all of the structures and functions of a living being. Most human DNA is nDNA, which is a huge molecule that is folded tightly and stored in the nucleus of the cell. MtDNA is a much smaller molecule stored in the mitochondria.

Dysarthria:  Disordered or impaired articulation of speech due to disturbances of muscular control, usually resulting from damage to the central or peripheral nervous system.
Dysarthria is associated with certain
neurodegenerative disorders, such as Parkinson's disease or Huntington's disease; cerebral palsy; brain tumors or stroke; or certain types of brain surgery. 
A difficulty with the physical production of speech, results largely from impairment of voluntary movement. Speech becomes slurred, dysrhythmic, variable in volume due to inconsistent breath support, and increasingly difficult to understand. Some patients do not seem to be aware of
distortions in their speech. For others, articulation is a constant source of frustration.
No medications are known to be helpful, and dysarthria may be worsened by agents which suppress chorea. However, several interventions may enhance communication in these patients. A communication board can also be useful in some cases. A speech-language pathologist may be able to
provide additional insights and manage-ment strategies. Dysarthria may be
compounded by cognitive problems found in HD, such as word-finding difficulty, difficulty initiating speech, or difficulty completing a sentence.
Unlike apraxia of speech, the speech errors that occur in dysarthria are highly consistent from one occasion to the next. Links: Dysarthria

Dyskinesias: Abnormal neuromuscular conditions characterized by disorganized or excessive movement (also known as hyperkinesia). Forms of dyskinesia include sudden, brief, "shock-like" muscle contractions (myoclonus); involuntary, rhythmic, oscillatory movements of a body part (tremor); rapid involuntary jerky movements (chorea); relatively slow writhing motions (athetosis); or abrupt, purposeless, simple or complex muscle movements or vocalizations (motor or vocal tics).

Dyskinesias while awake (DWA): Uncontrolled, sporadic movements of the legs and, in some cases, the arms. These movements may be very rapid (myoclonic) or quite slow and prolonged (dystonic); they usually disappear upon voluntary action. Some researchers suspect that these move-ments may represent a wakeful form of periodic limb movements in sleep (PLMS).

Dysphagia: Difficulty in swallowing. Dysphagia may be associated with esophageal obstruction as well as certain neurodegenerative or motor disorders involving the esophagus.
Results from impaired voluntary control
of the mouth and tongue, impaired respiratory control due to chorea, and impaired judgment, resulting in eating too rapidly, or taking overly large bites of food and gulps of liquid. Dry mouth, which can be brought on by neuroleptics, anti-depressants, and anticholinergics, may worsen the problem.
No medications are known to improve swllowing directly. Early referral to a speech-language pathologist will help identify swallowing difficulties, and periodic reassessment can identify changes in swallowing ability and suggest appropriate non-pharmacologic interventions such as a change in food consistency. Devices such as enlarged grips tor silverware and nonslip plates with raised edges to prevent spilling may prolong independent eating.

DYSPHASIA: Lack of coordination in speech, and failure to arrange words in an understandable way; due to brain lesion. Aphasia is the complete or near complete absence of speech, and is used to describe a more severe situation than dysphasia.

Dyspraxia: Partial loss of the ability to coordinate and perform certain purposeful movements and gestures in the absence of motor or sensory

Dystonia: A neurologic movement disorder characterized by sustained muscle contractions, resulting in repetitive, involuntary, twisting or writhing movements and unusual postures or positioning.
Dystonia may be limited to specific muscle groups (focal dystonia), such as dystonia affecting muscles of the neck (cervical dystonia or spasmodic torticollis) or the eyes, resulting in closure of the eyelids (blepharospasm). Dystonia is associated with certain underlying genetic disorders, such as dystonia musculorum deformans, dopa-responsive dystonia, and paroxysmal kinesigenic and paroxysmal non-kinesigenic dystonic choreoathetosis.
It can result in twisted, contorted postures of the body or limbs. The movements are usually slow and may appear exaggerated.
There are many causes of this movement disorder, which include biochemical abnormalities, degenerative disorders, psychiatric dysfunction, toxins, and drugs. The condition may result from the use of certain medications, lack of oxygen during or immediately after birth, or other causes of brain trauma. Many forms of dystonia are not well understood and occur as a primary syndrome.

Dystonic: Referring to dystonia; sudden jerky or repetitive movements and muscle spasms due to impaired muscle tone and abnormal muscle rigidity