A migraine is a complex neurological condition, not just a simple headache. Because migraines manifest in numerous ways, medical professionals rely on a formal classification system for an accurate diagnosis and effective treatment plan. The primary guide for this classification is the International Classification of Headache Disorders (ICHD), which provides a standardized framework for communication among clinicians and researchers worldwide.
Migraine With and Without Aura
The fundamental classification of migraine distinguishes between attacks that occur with or without an aura. Migraine without aura is the most common form. These attacks are characterized by a headache that can last from 4 to 72 hours and involves a pulsating pain of moderate to severe intensity, often localized to one side of the head. This head pain is frequently accompanied by other symptoms, such as nausea, vomiting, and a heightened sensitivity to light (photophobia) and sound (phonophobia).
About 25-30% of people experience migraine with aura. An aura consists of temporary and fully reversible neurological symptoms that usually precede or sometimes occur at the same time as the headache. These symptoms develop gradually over 5 to 20 minutes and last for less than an hour. The most common auras are visual, presenting as flashing lights, blind spots, or geometric zig-zag patterns that drift across the field of vision.
Beyond visual disturbances, auras can also manifest as sensory or speech-related symptoms. Sensory auras involve a tingling or numbness sensation, which starts in one hand, migrates up the arm, and may involve one side of the face or tongue. Some individuals may experience speech difficulties, known as aphasic aura. It is common for a person to experience both migraine with and without aura at different times.
Classification Based on Frequency
Beyond the presence or absence of an aura, migraines are also classified based on the frequency of headache days. This distinction is separate from the type of migraine and provides further detail for diagnosis. A person can have any migraine variant and also be classified by how often they experience attacks, which helps to determine the severity and impact of the condition.
Most individuals with migraine have episodic migraine. This diagnosis applies when a person experiences headaches on fewer than 15 days per month. The attacks can occur infrequently or more regularly, but the total number of headache days remains below this 15-day threshold.
When the frequency of headaches increases, the classification may shift to chronic migraine. The formal diagnostic criteria is having a headache on 15 or more days per month for longer than three months, with at least eight of those days featuring migraine characteristics. This progression from episodic to chronic migraine occurs in about 2.5% of people with episodic migraine each year. This classification is important because chronic migraine often indicates a more severe form of the disease and may require different treatment strategies.
Specific Migraine Variants
There are several less common but distinct migraine types identified by their unique symptoms. These variants have specific diagnostic criteria that set them apart from the more common forms. Understanding these types is important for diagnosis, as their symptoms can sometimes mimic other serious neurological conditions.
Hemiplegic migraine is a rare form of migraine with aura where the defining symptom is temporary motor weakness, or paralysis, on one side of the body (hemiplegia). This weakness can affect the face, arm, and leg, and is often accompanied by other typical aura symptoms. Because its symptoms so closely resemble a stroke, a first-time attack often requires emergency medical evaluation to rule out other causes. The motor symptoms usually resolve within 72 hours but can persist for weeks.
Migraine with brainstem aura involves symptoms understood to originate from the brainstem. Individuals experience at least two fully reversible symptoms such as vertigo, dysarthria (slurred speech), tinnitus, diplopia (double vision), or ataxia (impaired coordination). These brainstem-related symptoms distinguish this variant from typical migraine with aura, which does not include motor weakness.
Vestibular migraine is characterized by vertigo as the primary symptom. Episodes of moderate to severe vertigo, which can feel like the room is spinning or a sense of being off-balance, can last from minutes to days. A headache may or may not be present during these episodes. Other common symptoms include motion sensitivity, nausea, and unsteadiness.
Retinal migraine involves repeated attacks of temporary visual disturbances in only one eye. These disturbances can include shimmering lights, blind spots, or a complete, but reversible, loss of vision in that single eye. The symptoms last between five and 60 minutes and are often followed by a headache. The diagnostic feature is that the visual symptoms are monocular, whereas typical visual auras affect both eyes.
Complications of Migraine
A migraine attack can evolve into a more severe or prolonged event, which is classified as a complication. These are not distinct underlying types of migraine but descriptions of an attack that has become unusually persistent or severe. These situations often require prompt medical assessment.
The primary complication is status migrainosus. This is defined as a debilitating migraine attack that lasts for more than 72 consecutive hours. The headache pain is severe and may not respond to the person’s usual acute treatments. Because of the prolonged duration, individuals are at risk for issues like dehydration from persistent vomiting, necessitating medical care.
A much rarer complication is persistent aura without infarction. This is diagnosed when one or more aura symptoms last for a week or longer without any evidence of brain tissue injury (infarction) on neuroimaging studies. The symptoms can be disruptive and may persist for months or even years in some cases. A thorough diagnostic workup is necessary to differentiate this from a stroke or other causes.