Headaches and Migraine are classified by the International Headache Society as primary or secondary headaches (http://www.ichd-3.org).

Classification of Headache & Migraine

The majority of headache is primary (such as migraine). Primary headache is the best validated within this classification system (http://www.ichd-3.org).

Secondary headaches are precipitated by another condition or disorder, local or systemic. Serious causes of secondary headache are uncommon.

Common Primary Headache

Recurrent episodic headache

Recurrent episodic headache in isolation is most likely due to a primary headache disorder.

Headache which occurs on the majority of days in a month

Headache present for at least 15 days per month for over 3 months in isolation is most likely due to a primary headache disorder.

Strictly unilateral (right or left but never bilateral) headache most consistently occurs in the Trigeminal Autonomic Cephalalgias (TACS) (http://www.ichd-3.org). 11.5- 20% of migraine sufferers experience unilateral headache.

Bilateral headache more commonly occurs in migraine and is a more consistent defining feature of tension-type headache.

In most primary headache disorders the pain is experienced in the distribution of the first division of the trigeminal nerve and second cervical root. Neck pain can therefore be a feature of a migraine attack.

According to the International Classification of Headache disorders (ICHD), there are numerous descriptions of headache and multiple subsections, leading to over 100 classifications of different types of headaches, in fact you’d probably get a headache reading it!

Below is a useful table from ICHD which helps compare common primary headaches

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)