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The AHC Foundation is pleased to share resources to help our community understand the complexities of AHC. Below is a Glossary of terms related to AHC that can help families, teachers, therapists, caregivers, and friends understand the disorder.

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Abnormal ocular movements: Often the first symptom observed in patients with AHC. The abnormal movements may include nystagmus, esotropia and/or exotropia.

AHC Episode: A hemiplegic attack. Episodes may last anywhere from a few minutes to several days. AHC episodes are often associated with triggers that precede or induce the attack. Triggers for AHC episodes may include environmental conditions (such as temperature extremes or odors), water exposure, physical activities (exercise, swinging), lights (sunlight, fluorescent bulbs), and/or foods (chocolate, food dye) & medications.

Alternating Hemiplegia of Childhood Foundation (AHCF): The AHCF is a non-profit, tax-exempt organization started by parents of children and adults with AHC.

Athetoid movements: Continuous and flowing movements, resembling a twisting or writhing motion.

Ataxia: without coordination. Patients with ataxia experience a lack of coordination when performing voluntary movements. Ataxia is usually caused by dysfunction in the cerebellum, the part of the brain that controls movement and balance.

Autonomic Dysfunction: can be described as a disorder of the autonomic nervous system. (also see autonomic nervous system and nervous system)

Autonomic Nervous System (ANS): responsible for involuntary control of the heart, internal organs, glands and blood vessels. The sensory neurons of the ANS transmits messages from the body to the brain without our awareness. In response, the motor neurons of the ANS transmits automatic or reflex responses to maintain homeostatis in the body amidst our changing environment. The ANS is busy monitoring and maintaining your blood pressure, heart beat, body temperature, breathing rate, posture, and many other bodily functions. There are 3 divisions of the autonomic nervous system: the sympathetic, parasympathetic nervous system and the enteric nervous system.

Ataxia: a lack of muscle coordination which may affect speech, eye movements, the ability to swallow and eat, walking, picking up objects, and other voluntary movements.

Autonomic Dysfunction: a deviation from or interruption of the normal function of the autonomic nervous system which may include any of the following:

  • Heart rate (blood pressure)
  • Body temperature (perspiration)
  • Breathing rate
  • Digestion (Bowl and bladder functions)
  • Apnea
  • Metabolism (body weight)
  • Balance of water and electrolytes (such as sodium and calcium)
  • Production of body fluids (saliva, sweat, and tears)
  • Color changes
  • Pupillary abnormalities
  • Fatigue
  • Lightheadedness
  • Feeling faint or passing out
  • Impairment in the body’s ability to handle gravity


Behavioral Manifestations: occurrence of discrete episodes of failure to resist aggressive impulses that result in violent assault or destruction of property.

Bulbar Palsy: Bulbar palsy is the result of diseases affecting the lower cranial nerves. A speech deficit occurs due to paralysis or weakness of the muscles of articulation which are supplied by these cranial nerves.


Central Nervous System (CNS): The CNS is made up of the brain and the spinal cord.

Channelopathy: A group of diseases caused by the dysfunction of ion channels. Ion channels are passageways in the cell membranes of all cells. They control the movement of ions in and out of the cells. Ions are electrically charged particles, such as calcium, potassium, sodium and chloride. Ion channels control nerve function, heart contraction, movement, and various other important body processes, therefore ion channel dysfunction can cause many health problems. Ion channel dysfunction can affect any tissue in the body but it usually affects the muscular and nervous system.

Chorea: A type of abnormal movement characterized by recurrent, brief, unpredictable and purposeless body movements flow from one body part to another. The movements are briefer than those seen with dystonia but more sustained and less “shock like” than the movements seen with myoclonus.

Choreic Movements: May be sudden and jerky movements or may be more continuous and flowing. When they are more continuous and flowing, the term choreoathetosis is used.

Choreoathetosis: Ceaseless occurrence of rapid, highly complex jerky movements that appear to be well coordinated but are performed involuntarily. It is marked by 2 types of abnormal involuntary movements: chorea and athetosis.


Developmental Delay/Regression: important developmental milestone delay relating to motor, speech and language; cognition; social functioning; and activities of daily living

Diplegia/diparesis: the legs are affected more than the arms

Double hemiplegia/double hemiparesis: all four limbs are involved, but one side of the body is more affected than the other

Dysarthria: difficult or unclear articulation of speech that is otherwise linguistically normal.

Dyskinesia: A broad term for any abnormal involuntary movement.

Dysphagia: Difficulty in swallowing and chewing food – it takes more effort than normal to transport food from the mouth to the stomach. Drooling may occur as saliva collects in the mouth and they aren’t able to swallow.

Dystonia: Involuntary repetitive twisting and sustained muscle contractions. These result in abnormal movements and postures.

Dystonic movements: Abnormal movements that are usually rhythemic and repetitive, causing twisting movements and abnormal postures. Dystonia occurs when opposing muscles are contracting at the same time. The activation of these muscles may “overflow” to other muscle groups unintentionally.


EEG: An electroencephalogram (EEG) is a test used to detect abnormal electrical activity in the brain.

Enteric Nervous System: The digestive system is endowed with its own, local nervous system called the enteric nervous system. The enteric division contains neurons that control the digestive tract, pancreas, and gallbladder. Although the enteric nervous system can function independently, it is often regulated by the sympathetic and parasympathetic divisions.

Epilepsy: A chronic neurological disorder that results from the generation of abnormal electrical signals inside the brain, causing recurring seizures. A person is only considered to have epilepsy if he or she has had two or more seizures.

Episode: See AHC Episode

Esotropia: A form of strabismus (eye misalignment) in which one or both eyes turn inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a “cross-eyed” appearance. There are 4 main types of esotropia:

  1. Congenital (Infantile) Esotropia: This form develops within the first 6 months of infancy.
  2. Accommodative Esotropia: This form of esotropia is due to farsightedness and can usually be corrected with the use of farsighted glasses.
  3. Acquired Non-Accommodative Esotropia: This form of esotropia develops after infancy but does not correct with the use of farsighted glasses, thereby not falling into either of the first 2 categories.
  4. Pseudoesotropia: Pseudoesotropia is not a true form or esotropia/strabismus and the eyes are actually aligned correctly. The eyes appear crossed due to a broad bridge of the nose. As the child grows and the face matures, the crossed-eye appearance generally goes away.


Etiology: Refers to the origin of a disease. Etiology may refer to the cause of the disease or may describe certain factors that predispose someone to the disease.

Exotropia: A form of strabismus where the eyes have deviated outward.

Executive Functions: Consists of several mental skills that help the brain organize and act on information. These skills enable people to plan, organize, remember things, prioritize, pay attention and get started on tasks. They also help people use information and experiences from the past to solve current problems. Issues may include any of the following:

  • Impulse Control – ability to stop and think before acting
  • Emotional Control – ability to manage feelings by focusing on the end result or goal.
  • Flexibility – ability to roll with the punches and come up with new approaches when a plan fails.
  • Working Memory – ability to hold information in her mind and use it to complete a task.
  • Self-monitoring – ability to keep track of and evaluate her performance on regular tasks.
  • Planning and prioritizing – ability to come up with the steps needed to reach a goal and to decide their order of importance.
  • Task initiation- ability to get started on something
  • Organization – ability to keep track of information and things


Familial Hemiplegic Migraine (FHM): A genetic form of migraine headache. Migraines may be triggered by certain foods, emotional stress, and minor head trauma. Each headache may last from a few hours to a few days. Roughly 20 percent of people with FHM develop mild but permanent ataxia and nystagmus.

Flunarizine: A type of anticonvulsant drug known as a calcium channel blocker. It is traditionally used for the treatment of seizures, vertigo and migraines but is also used in the management of AHC patients. Flunarizine (5–20 mg/day) has been shown to decrease the severity, duration and frequency of AHC episodes in some patients with AHC[5],[6].


Hemiplegia/hemiparesis: Paralysis of one side of the body. The paralysis may involve the arm, leg and/or face on the affected side of the body.

Hemiplegic attack: Temporary paralysis affecting one side of the body. Patients with AHC experience repeated hemiplegic attacks which last anywhere from a few minutes to several days and may be associated with progressive neurologic deficits over time.

Hypertonia (Spasticity): Increased tightness of muscle tone and reduced capacity of the muscle to stretch

Hypertropia: A misalignment of the eyes where they turn upward.

Hypotonia: A state of low muscle tone (the amount of tension or resistance to stretch in a muscle), often involving reduced muscle strength.

Hypotropia: A misalignment of the eyes where they turn downward.


Monoplegia/monoparesis: Only one limb is affected

Mood Disorders: A group of diagnoses where a disturbance in the person’s mood in an underlying feature which may include any of the following:

  • Depression – Depressed mood or a loss of interest or pleasure in daily activities for more than two weeks.
  • Anxiety – An excessive anxiety and worry (apprehensive expectation), occurring more days than not for at least 6 months, about a number of events or activities (such as work or school performance).
  • Social Phobias – A persistent fear of one or more social or performance situations in which the person is exposed to unfamiliar people or to possible scrutiny by others. The individual fears that he or she will act in a way (or show anxiety symptoms) that will be embarrassing and humiliating.
  • Bipolar Disorder – characterized by the occurrence of at least one manic or mixed-manic episode during the patient’s lifetime. Most patients also, at other times, have one or more depressive episodes.
  • Psychosis – a disturbance that involves the sudden onset of at least one of the following positive psychotic symptoms: delusions, hallucinations, disorganized speech (e.g., frequent derailment or incoherence), or grossly abnormal psychomotor behavior, including catatonia

Motor Function Disorder: Delayed development of motor skills, or difficulty coordinating the movements that result in the child’s inability to perform daily tasks.

Movement Disorder: Movement disorders are a group of diseases that affect the ability to appropriate produce and control body movement. A movement disorder may affect the coordination and speed of voluntary movements. It may also involve excessive or involuntary movements.

MRI: Magnetic resonance imaging (MRI) is a medical procedure that uses a magnetic field and radio waves to produce pictures of organs and tissues within the body. An MRI allows doctors to examine the organs and tissues in order to diagnose a variety of problems, anywhere from heart disease to arthritis. MRIs are also used to assess conditions in the brain, such as tumors, stroke or developmental abnormalities.

Myoclonus: Refers to a type of movement disorder characterized by involuntary, rapid muscle contractions that result in a sudden, unexpected jerk or twitch.


Nervous System: is divided into 2 major parts: the central nervous system (CNS) and the peripheral nervous system (PNS).

Nystagmus: Rapid, involuntary movements on the eye. Movements may be horizontal (side-to-side), vertical (up and down) or rotary (circular). It may be congenital (meaning you are born with it) or acquired. People with nystagmus may have some level of vision impairment but the severity varies greatly from person to person. Nystatic movements may be classified as pendular or jerk.

  • Pendular nystagmus: eyes move back and forth at the same speed.
  • Jerk nystagmus: eyes move slowly in one directly and then quickly move back to the other direction, with a slow and fast phase. Such movements may be categorized as “upbeat”, where the fast phase occurs in an upward direction, or “downbeat” where the fast face is in the downward direction.


Paraplegia/paraparesis: the lower half of the body, including both legs, is affected.

Parasympathetic Nervous System: When there is little stress, the parasympathetic system tends to slow down the overall activity of the body. It causes the pupils to contract, it promotes digestion, and it slows the rate of heartbeat. This system is often referred to as the “rest and digest” response.

Paresis: means weakened

Paroxysmal: Is an episode of uncoordinated movement that occurs occasionally and then stops

Pentaplegia/pentaparesis: All four limbs are involved, with neck and head paralysis often accompanied by eating and breathing.

Peripheral Nervous System (PNS): The PNS is made up of nerves outside the brain and spinal cord. There are two types of nerve cells in the PNS: sensory neurons, which send information from the body to the CNS and motor neurons, which send information from the CNS to the rest of the body. The PNS can be further divided into 2 major parts: the somatic nervous system and the autonomic nervous system, both of which have both sensory and motor neurons.

Plegia: means paralyzed

PseudoBulbar Affect: A condition that causes uncontrollable crying and/or laughing that happens suddenly and frequently. A person having a PBA crying spell may cry when they don’t feel sad or when they only feel a little bit sad. Someone having a PBA laughing spell may laugh when they don’t feel amused or when they only feel a little bit amused.

Quadriplegia: A condition of paralysis in which a person loses complete or partial use of all limbs and the torso.


Seizures: A temporary disturbance in brain function caused by abnormal and excessive electrical impulses by a group of nerve cells. This disturbance in nerve cell activity can produce various symptoms, depending on which part and how much of the brain is affected. Seizures usually last from a few seconds to a few minutes and may produce changes in awareness or sensation, involuntary movements, or other behavioral changes. Seizures are classified as either focal or generalized; however, there are many types of seizures within these two categories.

  • Focal Onset – The term focal is used instead of partial to be more accurate when talking about where seizures begin. Focal seizures can start in one area or group of cells in one side of the brain.
  • Focal Onset Aware Seizures – When a person is awake and aware during a seizure, it’s called a focal aware seizure. This used to be called a simple partial seizure.
  • Focal Onset Impaired Awareness – When a person is confused or their awareness is affected in some way during a focal seizure, it’s called a focal impaired awareness seizure. This used to be called a complex partial seizure.
  • Generalized Onset – These seizures affect both sides of the brain or groups of cells on both sides of the brain at the same time.
  • Unknown Onset – When the beginning of a seizure is not known, it’s now called an unknown onset seizure. A seizure could also be called an unknown onset if it’s not witnessed or seen by anyone, for example when seizures happen at night or in a person who lives alone.
  • Motor symptoms of seizures include:
    • Clonic – sustained rhythmical jerking movements
    • Atonic – muscles becoming weak or limp
    • Tonic – muscles becoming tense or rigid
  • Non-motor symptoms of seizures include:
    • Absence – staring spells
    • Myoclonus – brief twitches

Somatic Nervous System: The sensory portion of the somatic nervous system conveys sensations from the body to the brain where it usually reaches our awareness, for example, when we touch something hot and feel pain. The motor portion of the somatic nervous system transmits impulses from the CNS to the body (namely the skeletal muscles), resulting in voluntary movements, for example when you move your hand off of the hot object in response to feeling pain. In other words, the SNS enables voluntary control of bones, joints, skin and skeletal muscle.

Status Epilepticus: Is said to occur when a seizure lasts too long or when seizures occur close together and the person doesn’t recover between seizures. Over the last several decades, the length of seizure that is considered as status epilepticus has shortened. Years ago, a seizure needed to last longer than 20 minutes to be considered status epilepticus. In the last few years, it is now defined as any seizure greater than 5 minutes. This makes sense because most seizures do not last longer than 2 minutes. The longer a seizure lasts, the less likely it will stop on its own without medication. Very long seizures (i.e., status epilepticus) are dangerous and even increase the chance of death. It is important that these long seizures are identified early, so they can be treated early.

Sympathetic Nervous System: The sympathetic nervous system stimulates the body. For example, it helps prepare the body to deal with emergency situations, which is why it is often referred to as the “fight or flight” response. Stimulation from sympathetic nerves dilates the pupils, accelerates the heartbeat, increases the breathing rate, and inhibits the digestive tract.

Strabismus: A misalignment of the eyes, where both eyes do not look at the same place at the same time. Strabismus may be caused by problems of the actual eye muscles, dysfunction of the nerves that send information to the eye muscles or impairment of the brain area that controls eye movements. Misalignment may be constant or intermittent, it may be unilateral (one eye) or bilateral (both eyes) and it may alternate from eye to eye (alternating).


Tetraplegia/tetraparesis: all four limbs are involved, but three limbs are more affected than the fourth

Triplegia/triparesis: Three limbs are affected. This could be both arms and a leg, or both legs and an arm. Or it could refer to one upper and one lower extremity and the face.

Trigger: In AHC, trigger is used to describe circumstances which precede or lead to an AHC episode. Specific triggers may include:

  • Environmental conditions (such as temperature extremes or odors),
  • Water exposure (About 1/3 of AHC patients have had an attack provoked by bathing, unrelated to the temperature of the water
  • Physical activities (exercise or motion, such as swinging)
  • Lights (bright sunlight or fluorescent lightbulbs)
  • Foods (such as chocolate or food dye)
  • Emotional response (anxiety, stress, fright)
  • Odors (foods, fragrances)
  • Fatigue
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