The International Headache Society (IHS) offers guidelines for the classification and diagnosis of migraine headaches, in a document called "The International Classification of Headache Disorders, 2nd edition" (ICHD-2). These guidelines constitute arbitrary definitions, and are not supported by scientific data.

• Childhood periodic syndromes that are commonly precursors of migraine include cyclical vomiting (occasional intense periods of vomiting), abdominal migraine (abdominal pain, usually accompanied by nausea), and benign paroxysmal vertigo of childhood (occasional attacks of vertigo).
• Retinal migraine involves migraine headaches accompanied by visual disturbances or even temporary blindness in one eye.
• Complications of migraine describe migraine headaches and/or auras that are unusually long or unusually frequent, or associated with a seizure or brain lesion.
• Probable migraine describes conditions that have some characteristics of migraines, but where there is not enough evidence to diagnose it as a migraine with certainty (in the presence of concurrent medication overuse).
• Chronic migraine, according to the American Headache Societyand the international headache society,  is a "complication of migraine"s and is a headache fulfilling the diagnostic criteria for "migraine headache", which occurs for a greater time interval. Specifically, greater or equal to 15 days/month for greater than 3 months.

  

Migraines typically present with recurrent severe headache associated with autonomic symptoms. An aura only occurs in a small percentage of people. The severity of the pain, duration of the headache, and frequency of attacks is variable. A migraine lasting 72 hours is termed status migrainosus and can be treated with intravenous prochlorperazine.
The four possible phases to a migraine attack  are listed below — not all the phases are necessarily experienced. Additionally, the phases experienced and the symptoms experienced during them can vary from one migraine attack to another in the same person:

1. The prodrome, which occurs hours or days before the headache
2. The aura, which immediately precedes the headache
3. The pain phase, also known as headache phase
4. The postdrome

  

For the 20–30% of migraine sufferers who experience migraine with aura, this aura comprises focal neurological phenomena that precede or accompany the attack. They appear gradually over five to 20 minutes and generally last fewer than 60 minutes. The headache phase of the migraine attack usually begins within 60 minutes of the end of the aura phase, but it is sometimes delayed up to several hours, and it can be missing entirely . The pain may also begin before the aura has completely subsided. Symptoms of migraine aura can be sensory or motor in nature.

Visual aura is the most common of the neurological events, and can occur without any headache. There is a disturbance of vision consisting often of unformed flashes of white and/or black or rarely of multicolored lights (photopsia) or formations of dazzling zigzag lines (scintillating scotoma, often arranged like the battlements of a castle, hence the alternative terms "fortification spectra" or "teichopsia"). Some patients complain of blurred or shimmering or cloudy vision, as though they were looking at an area above a heated surface, looking through thick or smoked glass, or, in some cases, tunnel vision and hemianopsia.

The somatosensory aura of migraine may consist of digitolingual or cheiro-oral paresthesias, a feeling of pins-and-needles experienced in the hand and arm, as well as in the nose-mouth area on the same side. The paresthesia may migrate up the arm and then extend to involve the face, lips and tongue.

Other symptoms of the aura phase can include auditory, gustatory or olfactory hallucinations, temporary dysphasia, vertigo, tingling or numbness of the face and extremities, and hypersensitivity to touch.

Oliver Sacks's book Migraine describes "migrainous deliria" as a result of such intense migraine aura that it is indistinguishable from "free-wheeling states of hallucinosis, illusion, or dreaming."

  

Enhancements reminiscent of a zigzag fort structure

Negative scotoma, loss of awareness of local structures

Positive scotoma, local perception of additional structures

Mostly one-sided loss of perception

The underlying cause of migraines is unknown. There are, however, many biological events that have been clinically associated with migraine.

Vascular
Serotonin
Melanopsin receptor
Neural

Migraines are underdiagnosed, and often are misdiagnosed. The diagnosis of migraine without aura, according to the International Headache Society, can be made according to the following criteria, the "5, 4, 3, 2, 1 criteria":

• 5 or more attacks - for migraine with aura, two attacks are sufficient for diagnosis.
• 4 hours to 3 days in duration
• 2 or more of the following:
  • Unilateral (affecting half the head);
  • Pulsating;
  • "Moderate or severe pain intensity";
  • "Aggravation by or causing avoidance of routine physical activity"
• 1 or more of the following:
  • "Nausea and/or vomiting";
  • Sensitivity to both light (photophobia) and sound (phonophobia)

The mnemonic POUNDing (Pulsating, duration of 4–72 hOurs, Unilateral, Nausea, Disabling) can help diagnose migraine. If four of the five criteria are met, then the positive likelihood ratio for diagnosing migraine is 24.

A migraine diary allows the assessment of headache characteristics, to differentiate between migraine and tension-type headache and to record the use and efficacy of acute medication. A diary also helps to analyse the relationship between migraine and menstruation. Finally, the diary can help to identify trigger factors. A trigger may occur up to 24 hours prior to the onset of symptoms; the majority of migraines, though, are not caused by identifiable triggers.

There are three main aspects of treatment -

1. Trigger avoidance,
2. Acute symptomatic control, and pharmacological prevention.
   

Medications are more effective --- if used earlier in an attack. The frequent use of medications may, however, result in medication overuse headache, in which the headaches become more severe and more frequent. These may occur with triptans, ergotamines, and analgesics, especially narcotic analgesics.

3. Interventional pain procedure - Trigeminal nerve block