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Tardive dyskinesia:

A movement disorder that may result from extended therapy with certain antipsychotic medications such as haloperidol. The condition is characterized by involuntary, rhythmic movements of the face, jaw, mouth, and tongue, such as lip pursing, chewing movements, or protrusion of the tongue. Facial movements are sometimes accompanied by involuntary, jerky or writhing motions (choreoathetoid movements) of the trunk, arms, and legs. In some patients, symptoms discontinue months or years after withdrawal of antipsychotic therapy. However, in others, the condition may not be reversible.

A form of tardive dyskinesia characterized by chronic dystonia due to administration of medications that block dopamine D2 receptors (dopamine receptor antagonists), such as certain antipsychotic agents. (Dopamine receptors are molecules on the surfaces of receiving nerve cells that are sensitive to stimulation by dopamine, a neurotransmitter that controls movement and balance. Several types of dopamine receptors have been identified, including D1, D2, and D3.) Dystonia is a neurologic movement disorder characterized by sustained muscle contractions that often result in repetitive twisting motions or unusual postures or positions. Tardive dystonia is the most common form of secondary dystonia–i.e., dystonia that results from certain environmental factors or “insults” that affect the brain. In adults, tardive dystonia often initially affects facial or neck muscles. Dystonia may remain limited to such regions or extend to affect adjacent muscles of the trunk and arms. Children are more likely to be affected by generalized dystonia that involves muscles of the trunk and legs.

Tardive dystonia:


Tauopathy refers to any group of diseases that cause dementia related to a problem with tau, a protein that is important in maintaining the structure of brain cells.

Tay-Sachs disease:

A progressive neurodegenerative metabolic disorder that belongs to a group of diseases called lysosomal storage diseases. Also known as GM2 gangliosidosis type I or infantile type, Tay-Sachs disease results from deficiency of the enzyme hexosaminidase A, which leads to an abnormal accumulation of certain fats (i.e., gangliosides) in particular tissues, particularly nerve cells of the brain. An autosomal recessive disorder, Tay-Sachs disease primarily affects individuals of northeastern European Jewish (Ashkenazi Jewish) ancestry. Symptom onset typically begins from about 3 to 6 months of age. Associated symptoms may include an exaggerated startle response, increasing listlessness, loss of previously acquired skills (psychomotor regression), severely diminished muscle tone (hypotonia), and the development of characteristic, cherry-red circular areas within the middle layers of the eyes (Tay’s sign). With disease progression, affected infants and children may develop increasing muscle stiffness or rigidity; seizures; sudden, involuntary, “shock-like” contractions of multiple muscle groups in response to certain stimuli (generalized, stimuli-sensitive myoclonus); enlargement of the brain (metabolic megalencephaly); deafness; blindness; and dementia. Life-threatening complications may develop between 2 to 5 years of age.


A tough fibrous cord of tissue that attaches muscle to bone (or other structures of the body).


Possessing the ability to disrupt normal fetal development and causing fetal abnormalities.


An area of the brain consisting of 2 relatively large masses of gray matter. The thalamus relays information from most sensory organs to the outer region of the cerebrum or cerebral cortex; receives and processes messages from the body concerning heat, cold, pain, pressure, and touch; and influences motor activity of the cerebral cortex.


A pain threshold is the point at which a feeling or sensation becomes painful.


 Involuntary, compulsive, stereotypic muscle movements or vocalizations that abruptly interrupt normal motor activities. These repetitive, purposeless motions (motor tics) or utterances (vocal tics) may be simple or complex in nature; may be temporarily suppressed; and are often preceded by a “foreboding” sensation or urge that is temporarily relieved following their execution. Simple tics include abrupt, isolated movements, such as repeated facial twitching, blinking, or shoulder shrugging, and simple sounds, including grunting, throat clearing, or sighing. Complex tics may involve more sustained, complex movements, such as deep knee bending or leg kicking, or complex vocalizations, including repeating another person’s words or phrases (echolalia) or, rarely, explosive cursing (coprolalia). Tourette syndrome is defined as the presence of multiple motor and vocal tics for at least one year, changes in the nature of the tics (e.g., complexity, severity, anatomical location) during the course of the disorder, and symptom onset before age 21.


Resistance or tension in a muscle when a limb or other body part is moved passively and in a relaxed state about a joint. A state of muscle tension balanced by partial contraction or alternate contraction and relaxation.


TorsinA is a protein that, when defective, may cause DYT-1 dystonia. Although its exact function is not known, TorsinA is believed to be related to a series of compounds that enable cells to recover from stress and injury.

Toxic metabolites:

A noninvasive scanning procedure during which a radioactive substance known as a radionuclide is introduced into the body to help evaluate the function and structure of certain organs or tissues. The amount of the substance taken up by particular tissues may depend upon the amount of blood flow within such regions. For example, absence of radionuclide uptake in a targeted region may indicate a lack of blood flow in certain areas. Following intravenous administration of the radioactive compound, a specialized rotating camera detects the radiation emanating from the radionuclides in the form of particles known as protons. The recorded images may produce colorized, horizontal and vertical cross sections and be reconstructed by computer to create three-dimensional images. By evaluating the blood supply to particular tissues, SPECT may be particularly helpful in detecting certain changes within the central nervous system or the heart.


A toxin is a poisonous substance that is produced by a plant or animal.


Temporary; transitory; not lasting or enduring.


Rhythmic, involuntary, oscillatory (or to-and-fro) movements of a body part.

Tropical spastic paraparesis

(HTLV-1-associated myelopathy):

A rare disorder characterized by slowly progressive weakness (paraparesis), stiffness (rigidity), and spasticity of the leg muscles due to infection with the human T-cell lymphotropic virus-1 (HTLV-1). Modes of transmission include sexual contact, mother-to-child transmission (e.g., via breastfeeding), and blood transfusion.


an essential amino acid.


an aromatic nonessential amino acid that is a metabolic precursor of thyroxine, the pigment melanin, and other biologically important compounds.

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