Glossary: Commonly Used Terms Found in Medical Literature — I-M

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iCT:  Intraoperative CT scan is a surgical room that also has a dual located CT scanner within the same room so that patients can undergo imaging during surgery and do not have to go back and forth to a separate room.  

Intraoperative MRI scan is a surgical room that also has a dual located MRI scanner within the same room so that patients can undergo imaging during surgery and do not have to go back and forth to a separate room. 

Iatrogenic: a response by a patient to one or more of the following causes: (1) medical treatment, (2) surgical treatment, (3) a procedure to help diagnose something, (4) a doctor, (5) a surgeon, and (6) exposure to the environment of a health care facility. The response is usually a bad one and the cause is usually accidental.

Idiopathic: A disorder or condition of spontaneous origin; self-originated or of unknown cause. The term is derived from the prefix "idio-" meaning one's own and "pathos" indicating disease.

Idiopathic epilepsy: Recurrent seizures of unknown origin or cause; repeated episodes of uncontrolled electrical activity in the brain that occur in the absence of detectable brain lesions. Also known as essential or primary epilepsy, these conditions are often thought to have a genetic component. This may suggest that affected individuals have an inherited predisposition for recurrent seizures.

Illusion: a misinterpreted perception that is caused by mistaking something present for something it is not. Illusions commonly occur with information that is seen or heard. For example, a common illusion is misinterpreting the noise made by wind for a voice. By contrast, a hallucination is a strong sensory perception that one has of an object or event while awake, when no such object or event exists. Whereas illusions involve misperceptions, hallucinations do not. Thus, an example of a hallucination would be hearing voices that are not really there and are not misinterpretation of the wind or any other noises.

Immunogenicity: The ability to or the degree to which a particular substance may provoke an immune response; having the properties of an antigen or any substance that may trigger a particular immune reaction, such as the production of antibodies.

Impedance: Relating to the electrical properties of the DBS. Also, has to do with the integrity of an implanted electrical system and the resistance to the flow of electrons along the implanted wire within that system.

Implantable Pulse Generator (IPG): A device that is placed under the skin near the collarbone as part of a surgical procedure known as deep brain stimulation. Wire leads from electrodes implanted in the brain are connected to the pulse generator, which then delivers continuous high frequency electrical stimulation to the thalamus via the implanted electrodes. This form of stimulation probably "jams" the nucleus and therefore modifies the message in the movement control centers of the brain, serving to suppress tremor.

Inhibition: The restraint, suppression, or arrest of a process or the action of a particular cell or organ; the prevention or slowing of the rate of a chemical or an organic reaction. The term "reciprocal inhibition" refers to the restraint or "checking" of one group of muscles upon stimulation (excitation) and contraction of their opposing (antagonist) muscles.

Inhibitor: 1. An agent that restrains or retards physiologic, chemical, or enzymatic action. 2. A substance that blocks, restricts, or interferes with a particular chemical reaction or other biologic activity.

Innervate: To supply a body part, tissue, or organ with nerves or nervous stimulation.

Insidious: Of subtle, gradual, or imperceptible development; referring to the development of symptoms that may not be recognized by an affected individual until the disorder in question is established.

Intonation: The rise and fall in pitch of the voice in speech.

Intravenous: Within a vein or veins, as in introducing certain substances, such as fluids, nutrients, or medications, directly into a vein.

Ion: An electrically charged atom or group of atoms due to the loss or gain of one or more electrons. Positively charged ions, known as cations, include potassium, calcium, sodium, hydrogen, ammonium, and magnesium. Negatively charged ions, called anions, include chloride, phosphate, and bicarbonate. The transfer of ions across cellular membranes plays an essential role in vital bodily processes, including enzyme activation, protein metabolism, acid-base balance, nerve impulse transmission, and muscle contraction.

Joint contractures: Permanent flexing or extension of joints in fixed postures due to shortening of muscle fibers. Contractures, abnormal fixation of the limbs, and associated deformity may result from prolonged immobility of developing joints.

Juvenile myoclonic epilepsy: A form of idiopathic epilepsy or recurrent seizures of unknown origin, with symptom onset typically occurring from approximately 12 to 16 years of age. The condition is characterized by sudden, involuntary, "shock-like" muscle jerks (myoclonus) that primarily occur during the morning or with stress, fatigue, or alcohol consumption. Patients may later develop generalized tonic-clonic seizures associated with loss of consciousness and rhythmic contraction and relaxation of all muscle groups.

Kinesigenic: Caused by sudden voluntary movement; movement induced. More specifically, this term is often used to describe abrupt episodes of involuntary movement that are provoked by sudden motions or unexpected stimuli.

Kinesiology: the science or study of the activity of muscles, and the functioning, mechanics, and structures of the body parts involved in movement. Mechanics refers to the effect that energy and other forces have upon the body.

Koniocellular layers: Part of the visual system that is involved with chromatic vision, specifically identifying the colors yellow-blue. This visual system can be affected by age as well as multiple diseases, including PD. See also Parvocellular and Magnocellular.

Lafora's disease: A progressive myoclonic encephalopathy (PME) that is inherited as an autosomal recessive trait. Associated symptoms typically begin in childhood or early adolescence and include frequent seizures characterized by loss of consciousness and rhythmic contraction and relaxation of all muscle groups (generalized tonic-clonic seizures); sudden, involuntary, "shock-like" muscle jerks (myoclonus); and rapidly progressive deterioration of thought processing and acquired intellectual abilities (dementia). Removal and microscopic examination of minute tissue samples (e.g., muscle fibers, liver cells, etc.) reveal abnormal, characteristic deposits of complex proteins and carbohydrates within the fluid portion of cells (intracytoplasmic inclusions known as "Lafora bodies").

Lance-Adams syndrome: Also known as "posthypoxic" or "postanoxic action myoclonus," this condition is characterized by the development of chronic action myoclonus due to a temporary lack or inadequate supply of oxygen to the brain (cerebral hypoxia or anoxia). Patients with action myoclonus experience sudden, involuntary, "shock-like" muscle contractions that may be triggered or aggravated by voluntary movement. Lance-Adams syndrome is also often associated with cerebellar ataxia or lack of coordination, postural imbalance, and other associated findings.

Laryngeal: The recess in each side of the wall of the larynx.

Lateral: Sideways; of, on, from, or toward the side.

Lateral ventricles: two curved openings (shaped like a horseshoe) located deep within the top section of the brain, that provide a pathway for cerebrospinal fluid. Cerebrospinal fluid is the fluid that protects the brain and spine from trauma. There is one lateral ventricle on each side of the brain. In addition to the two lateral ventricles, there is the third ventricle and the fourth ventricle. The two lateral ventricles are the largest of all the ventricles in the brain.

Lewy Body: Anormal collection of protein that develop inside nerve cells. Lewy bodies can be found in the brain of individuals with various diseases including Alzheimer's disease, Parkinson's disease, and Dementia with Lewy Bodies.

Limb kinetic apraxia: the same thing as motor apraxia. Some people use the term "limb kinetic apraxia" interchangeably with ideomotor apraxia.

Longitudinal: 1. Studied over a period of time. 2. Running lengthwise; in the direction of the long axis of the body or any of its parts.

Lumbar puncture: A procedure during which a sample of fluid (i.e., cerebrospinal fluid [CSF]) is removed from the spinal canal for diagnostic or therapeutic purposes. During the procedure, CSF is obtained via a hollow needle inserted between two bones of the spinal column within the lower back (i.e., usually the third and fourth lumbar vertebrae). Laboratory analysis conducted on CSF may help to diagnose central nervous system infections, certain tumors, or particular neurologic disorders. In some cases, lumbar puncture may also be performed to inject certain medications into the CSF, such as particular anticancer (chemotherapeutic) agents.

Lysosomal: Referring to lysosomes, which are membrane-bound bodies (organelles) outside the nuclei of cells that contain various enzymes engaged in intracellular digestion.

Lysosomal storage diseases: Inborn errors of metabolism in which deficiency or impaired functioning of particular lysosomal enzymes leads to an abnormal accumulation of certain substances (e.g., fats, complex carbohydrates) within particular cells, progressively affecting multiple bodily tissues and organs. (Lysosomes are membrane-bound, enzyme-containing bodies within cells that engage in digestive processes; enzymes are proteins that accelerate the rate of certain chemical reactions in the body.) Most lysosomal storage disorders (e.g., mucolipidoses, mucopolysaccharidoses, lipidoses, etc.) are thought to be inherited as autosomal recessive traits.

Machado-Joseph disease: Machado-Joseph disease, also known as spinocerebellar ataxia (SCA) type III, is probably the most common autosomal dominant SCA. This disorder was previously known as Azorean disease, as a large number of Portuguese families from the Azores Islands were found to be affected; however, SCA type III has now been reported in many other ethnic groups. In addition to unsteadiness of gait (ataxia), symptoms may involve parkinsonism, dystonia, and chorea. The affected protein is called ataxin-3; however, its function is not yet known.

Magnetic resonance imaging (MRI): A diagnostic scanning technique during which radio waves and an electromagnetic field are used to help create detailed, cross-sectional images of specific organs and tissues. MRI is often considered a particularly valuable imaging technique for studies of the brain and spinal cord because of the MRI’s ability to scan images from various angles and provide strong contrast between healthy and abnormal tissues.

Magnocellular layers: Part of the visual system that is involved with achromatic vision, specifically luminence or brightness. Very important system when discussing contrast sensitivity. This visual system can be affected by age as well as multiple diseases, including PD. See also Parvocellular and Koniocellular.

MAO-B inhibitors: Inhibitors of the enzyme monoamine oxidase B. MAO-B helps break down dopamine; inhibiting it prolongs the action of dopamine in the brain.

Mean: An average; intermediate or middle position in value, quantity, or degree. The "arithmetic mean" is a statistical measure derived by adding a set of values and dividing the total by the number of values.

Medially: Toward the middle; closer to or oriented toward the midline or median plane of a body or structure. The "median plane" refers to the imaginary plane that divides a body into symmetrical parts.

MERFF syndrome (myoclonus epilepsy with ragged-red fibers): A rare hereditary disorder characterized by neurologic and muscle abnormalities due to defects of genetic material (DNA) in mitochondria, the rod-like structures outside the nuclei of cells that serve as a primary source of cellular energy. Removal and microscopic examination of minute samples of muscle fibers reveal structurally abnormal mitochondria (a finding known as "ragged-red fibers"). Associated symptoms include muscle weakness; sudden, involuntary, "shock-like" muscle contractions induced by voluntary movements or in response to external stimuli (action or reflex myoclonus); repeated seizures (epilepsy); progressively impaired coordination of voluntary movements (ataxia); and/or gradual deterioration of intellectual functioning (dementia). Some affected individuals may also have additional abnormalities, such as hearing loss; degeneration of the nerves (i.e., optic nerves) that convey impulses from the retinas to the brain (optic atrophy); short stature; heart muscle disease (cardiomyopathy); or other findings.

Metabolism: Refers to the ongoing chemical processes of cells of the body, including catabolism and anabolism. Catabolism or so-called "destructive metabolism" is the breakdown of complex chemical compounds into simpler substances, typically liberating or releasing energy. In contrast, anabolism or "constructive metabolism" refers to the "building up" or conversion of simple substances into more complex chemical compounds, requiring energy consumption (provided by catabolic processes).

Micrographia:  A disorder of written expression where one’s writing becomes very small.

Micturition: Urination.

Mitochondrial: Referring to mitochondria or rod-like structures inside cells of the body whose primary functions include the production and regulation of energy.

MMSE: an abbreviation for the Mini-Mental State Examination, a brief test of cognitive status.

Monoamine: A molecule containing one amine group. An amine is an organic compound containing nitrogen. The so-called "biogenic monoamines" are natural, biologically active compounds that often function as neurotransmitters, including dopamine, serotonin, noradrenaline, and epinephrine.

Monotherapy: A drug used alone to treat a disease (opposite of combination therapy).

Motor apraxia: a disturbance of voluntary movement in which one cannot use objects for the purposes for which they were designed. However, the affected individual still knows for what the object should be used. Motor apraxia is caused by lesions to the premotor cortex (an area near the middle of the brain that is important for movement) on the opposite site of the affected limb.

MR-guided focused ultrasound (MRgFUS): A non-invasive thermal ablative treatment that utilizes ultrasound to produce a lesion.  Temporary or permanent lesions can be created.

Multiple sclerosis (MS): a disease in which a loss of a substance around nerve fibers in the brain and/or spine causes motor difficulties. MS is a progressive disease of the central nervous system characterized by destruction of myelin (demyelination), the fatty substance that forms a protective sheath around certain long nerve fibers (axons). Myelin serves as an electrical insulator, enabling the effective transmission of nerve signals. Patients with MS may develop paresthesias, such as numbness or tingling; muscle weakness and stiffness; impaired coordination; abnormal reflexes; an inability to control urination (urinary incontinence); slurred speech; visual disturbances; and/or other symptoms and findings.

Muscle tone: The low level of contraction in a muscle not being intentionally contracted.

Mutation: A change in a gene, such as loss, gain, or substitution of genetic material, that alters its function or expression. This change is passed along with subsequent divisions of the affected cell. Gene mutations may occur randomly for unknown reasons or may be inherited.

Myalgia: Muscular pain.

Myelin: The whitish, fatty substance forming the segmented, multilayered wrappings or "sheaths" around certain long nerve fibers or axons. Myelin sheaths electrically insulate axons, serving to speed the transmission of nerve signals (action potentials).

Myelinated: Referring to long nerve fibers (axons) that have myelin sheaths. Consisting of segmented, multilayered wrappings of myelin, a whitish protein, myelin sheaths wrap around certain nerve fibers, providing electrical insulation and serving to speed the transmission of nerve signals.

Myoclonic: Pertaining to myoclonus or irregular, involuntary, shock-like contractions or spasms of a muscle or muscle group.

Myoclonus: A neurologic movement disorder characterized by brief, involuntary, twitching or "shock-like" contractions of a muscle or muscle group. These jerk-like movements may be accompanied by periodic, unexpected interruptions in voluntary muscle contraction, leading to lapses of sustained posture (known as "negative myoclonus"). So-called "positive" and "negative" myoclonus are often seen in the same individuals and may affect the same muscle groups. Myoclonus is often a nonspecific finding, meaning that it may occur in the setting of additional neurologic abnormalities and be associated with any number of underlying conditions or disorders. In other patients, myoclonus appears as an isolated or a primary finding. Depending on the underlying cause and other factors, the shock-like muscle jerks may occur repeatedly or infrequently; may tend to appear under specific circumstances (e.g., with voluntary movements or in response to specific external sensory stimuli); and may affect any body region or regions.