Current Headache Classification
The current classification of headaches is based on the International Classification of Headache Disorders, Third Edition (ICHD-3), published in 2018, which divides headaches into three major parts: primary headaches, secondary headaches, and painful cranial neuropathies/facial pain. 1, 2, 3
Three-Part Structure
The ICHD-3 organizes all headache disorders into:
- Part 1: Primary Headaches - idiopathic headaches with no underlying structural or systemic cause 4, 2
- Part 2: Secondary Headaches - symptomatic headaches caused by underlying conditions 4, 2
- Part 3: Painful Cranial Neuropathies, Other Facial Pain, and Other Headaches 2, 5
Primary Headache Categories
The four main categories of primary headaches include:
1. Migraine 1, 5
Migraine without aura requires at least 5 attacks with headaches lasting 4-72 hours (untreated), at least two of the following characteristics: unilateral location, pulsating quality, moderate-to-severe intensity, or aggravation by routine physical activity, and at least one of nausea/vomiting or photophobia plus phonophobia. 1
Migraine with aura requires at least 2 attacks with one or more fully reversible aura symptoms (visual, sensory, speech/language, motor, brainstem, or retinal), with at least three specific characteristics including gradual spread over ≥5 minutes, individual symptoms lasting 5-60 minutes, and aura accompanied by or followed by headache within 60 minutes. 1
Chronic migraine is defined as headache occurring on ≥15 days/month for >3 months, with migraine features on ≥8 days/month. 1
2. Tension-Type Headache 1, 6
This requires at least two of the following: pressing/tightening (non-pulsatile) character, mild-to-moderate intensity, bilateral location, and no aggravation with routine activity, plus both no nausea/vomiting (anorexia allowed) and no more than one of photophobia or phonophobia. 1, 6
3. Cluster Headache and Other Trigeminal Autonomic Cephalalgias 1, 6, 5
Cluster headache requires five attacks with severe unilateral orbital/supraorbital/temporal pain lasting 15-180 minutes (untreated), occurring with a frequency of one to eight attacks daily, accompanied by at least one ipsilateral autonomic symptom (lacrimation, nasal congestion, rhinorrhea, facial sweating, ptosis, miosis, or eyelid edema). 1, 6
4. Other Primary Headaches 5
This category includes previously unclassified primary headaches such as hypnic headache, hemicrania continua, and benign thunderclap headache. 7, 5
Secondary Headache Categories
Eight categories of secondary headaches are recognized, attributed to underlying conditions such as head/neck trauma, vascular disorders, infections, medication overuse, or structural lesions. 4, 5
Medication-overuse headache specifically requires headache on ≥15 days/month in someone with pre-existing headache disorder, with regular overuse for >3 months of acute medications (non-opioid analgesics on ≥15 days/month or other acute medications on ≥10 days/month). 1
Key Classification Principles
The ICHD-3 is phenomenological rather than etiological, classifying the headache as a clinical entity rather than the patient, meaning one patient can have multiple headache diagnoses simultaneously. 4
The classification contains 14 different headache groups and more than 170 specific headache types, representing significant expansion from earlier editions. 4, 3
Important caveat: The ICHD-3 criteria require specific numbers of attacks and symptom combinations, which means early presentations may not meet full diagnostic criteria and should be coded as "probable" subtypes until sufficient attacks occur. 1