Headache & Migraine Classification

Headaches and migraines are classified by the International Headache Society (ICHD-3) as either primary or secondary headaches (ICHD-3.org).

Primary vs Secondary Headache

  • Primary headache is the most common category and includes conditions such as migraine and tension-type headache. These are not caused by another underlying condition but represent a disorder in their own right.

  • Secondary headache occurs as a result of another disorder or condition, either local (e.g., sinus disease) or systemic (e.g., hypertension, infection). Serious secondary causes are uncommon but must be considered in diagnosis.

Common Primary Headache Presentations

  • Recurrent episodic headache
    Headaches that occur intermittently are most often due to a primary headache disorder.

  • Chronic daily headache
    Headache present on 15 or more days per month for over 3 months—without another cause—is usually a primary headache disorder.

  • Unilateral headache
    Strictly one-sided headache (always right or always left, never both) most consistently occurs in the Trigeminal Autonomic Cephalalgias (TACs). Around 11.5–20% of migraine sufferers experience this unilateral pattern.

  • Bilateral headache
    More common in migraine and a defining feature of tension-type headache.

Pain Distribution in Primary Headache

In many primary headache disorders, pain follows the distribution of the first division of the trigeminal nerve and the second cervical root. This explains why neck pain is often a feature of migraine attacks.

The Complexity of Headache Classification

The International Classification of Headache Disorders (ICHD) provides detailed descriptions and multiple subcategories, resulting in over 100 different headache types. The sheer breadth of classification highlights the complexity of diagnosis—enough to give anyone a headache just reading through it!

Classification of Headache & Migraine

The most consistent indicators for serious secondary headache are:

Thunderclap (sudden onset) headache

Sudden onset headache reaching maximum intensity within 5 minutes is called thunderclap headache. Thunderclap headache has the greatest probability of a secondary precipitant.

Associated focal neurological deficit

Evolution of headache over days to weeks. If associated systemic features and/or focal neurological signs develop, there is an increased probability of secondary precipitant.

Associated systemic features

Patients over the age over 50 years (especially with new onset headache)