Definitions of terms

Accompanying symptoms: Symptoms that typically accompany rather than precede or follow headache. In migraine, for example, the most frequent accompanying symptoms are nausea, vomiting, photophobia and phonophobia.

Allodynia: Sensation of discomfort or pain (qv) arising from a stimulus that would not normally be sufficient to have this effect. It is distinguished from hyperalgesia (qv).

Anorexia: Lack of appetite and dislike for food to a mild degree.

Attack of headache (or pain): Headache (or pain) (qv) that builds up, remains at a certain level for minutes, hours or days, then wanes until it has resolved completely.

Attributed to: This term in ICHD-3 describes the relationship between a secondary headache (qv) and the disorder believed to cause it. It requires fulfilment of criteria establishing an accepted level of evidence of causation.

Aura: Early symptoms of an attack of migraine with aura, believed to be the manifestations of focal cerebral dysfunction. The aura typically lasts 20-30 minutes and precedes the headache (qv). See also: Focal symptoms, Prodrome, Premonitory symptoms and Warning symptoms.

Central neuropathic pain: Pain (qv) caused by a lesion or disease of the central somatosensory nervous system (see also Neuropathic pain).

Chronic: In pain terminology, chronic signifies long-lasting, specifically over a period exceeding 3 months. In headache terminology, it retains this meaning for secondary headache disorders (notably those attributed to infection) in which the causative disorder is itself chronic. In this usage, chronic is distinguished from persistent (qv). For primary headache disorders that are more usually episodic (qv), chronic is used whenever attacks of headache (qv) occur on more days than not over a period longer than 3 months. The trigeminal autonomic cephalalgias are the exception: in these disorders, chronic is not used until the disorder has been unremitting for more than one year.

Close temporal relation: This term describes the relation between an organic disorder and headache. Specific temporal relations may be known for disorders of acute onset where causation is likely, but have often not been studied sufficiently. For chronic disorders the temporal relation as well as causation are often very difficult to ascertain.

Cluster headache attack: One episode of continuous pain lasting 15-180 minutes.

Cluster period: The time during which cluster headache attacks occur regularly and at least once every other day (also referred to as cluster bout).

Cluster remission period: The time during which attacks cease to occur spontaneously and cannot be induced with alcohol or nitroglycerine. To be considered a remission, the attack-free period must exceed 3 months.

Duration of attack: Time from onset until termination of an attack of headache (or pain) (qv) meeting criteria for a particular headache type or subtype. After migraine or cluster headache, a low-grade non-pulsating headache without accompanying symptoms may persist, but this is not part of the attack and is not included in duration. If the patient falls asleep during an attack and wakes up relieved, duration is until time of awakening. If an attack of migraine is successfully relieved by medication but symptoms recur within 48 hours, these may represent a relapse of the same attack or a new attack. Judgement is required to make the distinction (see also Frequency of attacks).

Enhanced entoptic phenomena: Visual disturbances arising from the structure of the visual system itself, including excessive floaters in both eyes, excessive blue field entoptic phenomenon (uncountable little grey/white/black dots or rings shooting over the visual field of both eyes when looking at homogeneous bright surfaces such as the blue sky), self-lighting of the eye (coloured waves or clouds perceived when closing the eyes in the dark) and spontaneous photopsia (bright flashes of light).

Episodic: Recurring and remitting in a regular or irregular pattern of attacks of headache (or pain) (qv) of constant or variable duration. Through long usage the term has acquired special meaning in the context of episodic cluster headache, referring to the occurrence of cluster periods (qv) separated by cluster remission periods (qv) rather than to attacks. Similar usage has been adopted for paroxysmal hemicrania and short-lasting unilateral neuralgiform headache attacks.

Facial pain: Pain below the orbitomeatal line, anterior to the pinnae and above the neck.

Focal neurological symptoms: Symptoms of focal brain (usually cerebral) disturbance such as occur in migraine aura (qv).

Fortification spectrum: Angulated, arcuate and gradually enlarging visual disturbance typical of migrainous visual aura, which can be coloured or black-and-white.

Frequency of attacks: The rate of occurrence of attacks of headache (or pain) (qv) per time period (commonly one month). Successful relief of a migraine attack with medication may be followed by relapse within 48 hours. The IHS Guidelines for Controlled Trials of Drugs in Migraine, 3rd edition, recommend as a practical solution, especially in differentiating attacks recorded as diary entries over the previous month, to count as distinct attacks only those that are separated by at least 48 hours headache-free.

Headache: Pain (qv) located in the head, above the orbitomeatal line and/or nuchal ridge.

Headache days: Number of days during an observed period of time (commonly one month) affected by headache for any part or the whole of the day.

Heterophoria: Latent strabismus (squint).

Heterotropia: Manifest strabismus (squint).

Hypalgesia: Diminished perception in response to a stimulus expected to be painful.

Hyperalgesia: Heightened perception in response to a stimulus expected to be painful. Hyperalgesia is distinguished from allodynia (qv), arising from a stimulus not expected to be painful.

Intensity of pain: Level of pain (qv), usually scored on a four-point numerical rating scale (0-3) equivalent to no, mild, moderate and severe pain, or on a visual analogue scale (commonly 10 cm). It may also be scored on a verbal rating scale expressed in terms of its functional consequence: 0, no pain; 1, mild pain, does not interfere with usual activities; 2, moderate pain, inhibits but does not wholly prevent usual activities; 3, severe pain, prevents all activities.

Lancinating: Brief, electric-shock-like character of pain (qv), along a root or nerve distribution.

Neuralgia: Pain (qv) in the distribution(s) of a nerve or nerves, presumed to be due to dysfunction or injury of those neural structures. Common usage has implied a paroxysmal or lancinating (qv) quality, but the term neuralgia should not be reserved for paroxysmal pains.

Neuritis: A special case of neuropathy (qv); the term is now reserved for inflammatory processes affecting nerves.

Neuroimaging: computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), single-photon emission computed tomography (SPECT) or scintigraphy, including functional modalities where applicable, usually of the brain.

Neuropathic pain: Pain (qv) caused by a lesion or disease of the peripheral or central somatosensory nervous system.

Neuropathy: A disturbance of function or pathological change in a nerve or nerves (in one nerve: mononeuropathy; in several nerves: mononeuropathy multiplex; when diffuse and bilateral: polyneuropathy). The term neuropathy is not intended to cover neurapraxia, neurotmesis, axonotmesis, section of a nerve, disturbances of a nerve due to transient impact such as a blow, stretching or epileptic discharge (the term neurogenic applies to pain attributed to such temporary perturbations).

New headache: Any type, subtype or subform of headache (qv) from which the patient was not previously suffering.

Not sufficiently validated: Of doubtful validity as a diagnostic entity judged from the experience of the classification committee members and/or controversy in the literature.

Nuchal region: Dorsal (posterior) aspect of the upper neck including the region of insertion of neck muscles on the cranium.

Nyctalopia: Impaired night vision.

Pain: According to the IASP definition: an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage (see also: Neuropathic pain, Central neuropathic pain and Peripheral neuropathic pain).

Palinopsia: Visual disturbances in the form of after-images and/or trailing images of moving objects (to be distinguished from retinal after-images, which occur, in complementary colour, after staring at a high contrast image).

Pericranial muscles: Neck and occipital muscles, muscles of mastication, facial muscles of expression and speech and muscles of the inner ear (tensor tympani, stapedius).

Peripheral neuropathic pain: Pain (qv) caused by a lesion or disease of the peripheral somatosensory nervous system (see also Neuropathic pain).

Persistent: This term, used in the context of certain secondary headaches, describes headache, initially acute and caused by another disorder, that fails to remit within a specified time interval (usually 3 months) after that disorder has resolved. In many such cases, the headache is recognized as a distinct subtype or subform, with evidence of causation depending upon earlier fulfilment of the criteria for diagnosis of the acute type, and persistence of the same headache.

Phonophobia: Hypersensitivity to sound, even at normal levels, usually causing avoidance.

Photophobia: Hypersensitivity to light, even at normal levels, usually causing avoidance.

Postdrome: A symptomatic phase, lasting up to 48 hours, following the resolution of pain in migraine attacks with or without aura. Among the common postdromal symptoms are fatigue, elated or depressed mood and cognitive difficulties.

Premonitory symptoms: This term has been used with different meanings, often synonymously with prodrome (qv) but also, less specifically and somewhat ambiguously, for a range of symptoms believed to forewarn of (but possibly the initial phase of) a migraine attack. The term is better avoided.

Pressing/tightening: Pain (qv) of a constant quality, often compared to a tight band around the head.

Previously used term: A diagnostic term that has been used previously with a similar or identical meaning to the classified term or is subsumed within it. Previously used terms are often ambiguous and/or have been used differently in different countries.

Primary headache (disorder): Headache, or a headache disorder, not caused by or attributed to another disorder. It is distinguished from secondary headache disorder (qv).

Prodrome: A symptomatic phase, lasting up to 48 hours, occurring before the onset of pain in migraine without aura or before the aura in migraine with aura. Among the common prodromal symptoms are fatigue, elated or depressed mood, unusual hunger and cravings for certain foods.

Pulsating: Characterized by rhythmic intensifications in time with the heart beat; throbbing.

Punctate stimuli: Stimuli applied to discreet points on the skin.

Referred pain: Pain (qv) perceived in another area than the one where nociception arises.

Refractory period: The time following resolution of an attack of pain (qv) during which a further attack cannot be triggered.

Refraction (or refractory) error: Myopia, hypermetropia or astigmatism.

Resolution: Complete remission of all symptoms and other clinical evidence of disease or a disease process (such as an attack of headache [qv]).

Scintillation: Visual hallucinations that are bright and fluctuate in intensity, often at approximately 8-10 cycles/second. They are typical of migraine aura (qv).

Scotoma: Loss of part(s) of the visual field of one or both eyes. Scotoma may be absolute (no vision) or relative (obscured or reduced vision). In migraine, scotomata are homonymous.

Secondary headache (disorder): Headache, or a headache disorder, caused by another underlying disorder. In ICHD-3, secondary headaches are attributed to the causative disorder. Secondary headaches are distinguished from primary headaches (qv). A secondary headache may have the characteristics of a primary headache but still fulfil criteria for causation by another disorder.

Stab of pain: Sudden pain (qv) lasting a minute or less (usually a second or less).

Strabismus: Abnormal alignment of one or both eyes (squint).

Substance: Any of the following: organic or inorganic chemical; food or additive; alcoholic beverage; gas or vapour; drug or medication or herbal, animal or other substance given with medicinal intent although not licensed as a medicinal product.

Teichopsia: Synonym for fortification spectrum (qv).

Tenderness: A heightened feeling of discomfort or pain caused by direct pressure such as is applied during palpation.

Throbbing: Synonym for pulsating (qv).

Unilateral: On either the right or the left side, not crossing the mid line. Unilateral headache does not necessarily involve all of the right or left side of the head, but may be frontal, temporal or occipital only. When used for sensory or motor disturbances of migraine aura, the term includes complete or partial hemidistribution.

Vasospasm: Constriction of artery or arterioles to such a degree that tissue perfusion is reduced.

Warning symptoms: Previously used term for either aura (qv) or premonitory symptoms (qv), and therefore ambiguous. It should not be used.

Withdrawal: Interruption in use of or exposure to a medication or other substance that has lasted for weeks or months. The term embraces but is not limited to therapeutic withdrawal (cessation) of medication in the context of medication-overuse headache.

Zigzag line: Synonym for fortification spectrum (qv).