Causes of Headaches
Headaches are broadly classified into primary headache disorders (migraine, tension-type headache, and cluster headache), which account for approximately 98% of all headaches, and secondary headaches caused by underlying pathology that must be systematically excluded before diagnosing a primary disorder 1, 2.
Primary Headache Disorders
Migraine
Migraine is the most disabling primary headache disorder and the second leading cause of global disability 3, 4. It presents as:
- Recurrent attacks lasting 4-72 hours (2-72 hours in children/adolescents under 18)
- At least 2 of these features: unilateral location, pulsating quality, moderate-to-severe intensity, aggravation by routine physical activity
- At least 1 associated symptom: nausea/vomiting OR photophobia and phonophobia
- Requires ≥5 attacks meeting these criteria for diagnosis 5, 1
Important clinical pearl: Bilateral pain occurs in approximately 40% of migraine patients, so unilateral location is not required 1.
Migraine with aura (affects one-third of migraine patients) includes transient focal neurological symptoms—most commonly visual (>90%), such as fortification spectra, or sensory symptoms (31%), typically unilateral paresthesias spreading gradually in face or arm 1.
Chronic migraine is diagnosed when headaches occur ≥15 days/month for ≥3 months, with ≥8 days/month meeting migraine criteria 6, 4.
Tension-Type Headache
The most common primary headache, characterized by:
- Pressing/tightening (non-pulsatile) quality
- Mild-to-moderate intensity
- Bilateral location
- No aggravation with routine activity
- Absence of nausea/vomiting (anorexia may occur)
- Absence of both photophobia AND phonophobia (one may be present) 7
Cluster Headache
Presents with:
- 5 attacks with frequency of 1-8 attacks daily
- Severe unilateral orbital/supraorbital/temporal pain lasting 15-180 minutes
- Ipsilateral autonomic features: lacrimation, nasal congestion, rhinorrhea, facial sweating, ptosis, miosis, or eyelid edema 7
Secondary Headache Disorders
Secondary causes require immediate recognition as they can be life-threatening. The key is identifying "red flags" that mandate urgent investigation 8, 9.
Critical Red Flags Requiring Immediate Evaluation
- Thunderclap headache (sudden, severe onset) → subarachnoid hemorrhage
- Progressive headache → intracranial mass lesion
- Headache with fever and neck stiffness → meningitis
- Focal neurological symptoms/signs → stroke, mass lesion
- Head trauma → subdural hematoma
- New-onset headache after age 50 → temporal arteritis, secondary causes
- Headache worsened by Valsalva, coughing, sneezing, or position changes → intracranial hypertension/hypotension
- Unexplained weight loss, altered consciousness, or personality changes → systemic disease, mass lesion 1, 8, 9
Common Secondary Causes by Category
Vascular causes:
- Temporal (giant cell) arteritis—particularly in elderly patients
- Subarachnoid hemorrhage
- Stroke/transient ischemic attack
- Subdural hematoma 8
Intracranial causes:
Systemic/metabolic causes:
- Hypertensive encephalopathy
- Electrolyte disturbances (calcium abnormalities)
- Metabolic and endocrine disorders 11
Medication-related:
- Medication overuse headache (from opioids, triptans, ergotamine, caffeine-containing analgesics, butalbital)
- Drug-induced aseptic meningitis (ibuprofen, immunoglobulins, antibiotics)
- Nitrates, calcium channel blockers 12, 11
Diagnostic Approach
Neuroimaging is NOT routinely indicated for primary headache disorders with normal neurological examination 1.
Neuroimaging IS indicated when:
- Red flags are present
- Atypical headache patterns
- Focal neurological signs
- Rapidly increasing headache frequency
- Headache awakening patient from sleep
- History of uncoordination
- Persistent headache following head trauma
- Marked change in established headache pattern 7
EEG is not useful in routine headache evaluation unless seizure disorder or atypical migrainous aura is suspected 7.
Special Populations
Elderly patients (≥65 years): Higher risk of secondary causes including temporal arteritis, subdural hematomas, CNS tumors, and strokes. Require complete neurological examination and lower threshold for investigating secondary causes 8.
Children/adolescents: Headache presentation differs from adults; attacks may be shorter (2-72 hours vs 4-72 hours). Common primary causes are migraine and tension-type headache. Secondary causes include infections, trauma, vascular disorders, and substance use/withdrawal 13.
Common Pitfalls
- Assuming bilateral headache excludes migraine—40% of migraine patients have bilateral pain 1
- Missing vestibular migraine—can closely mimic other vestibular disorders and requires specific diagnostic criteria 5
- Overlooking medication overuse headache—occurs with frequent use (>2 days/week) of acute headache medications 1, 12
- Failing to recognize that pre-existing primary headache does not exclude secondary headache—pattern changes require re-evaluation 9