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differential diagnosis of headache primary secondary causes
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headache red flags serious secondary causes meningitis subarachnoid hemorrhage hypertension
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Differential Diagnosis of Headache
Headaches are broadly classified into Primary (no underlying structural/systemic cause) and Secondary (due to an identifiable underlying disorder).
PRIMARY HEADACHE DISORDERS
These are diagnoses of exclusion after ruling out secondary causes.
| Type | Key Features |
|---|---|
| Migraine | Unilateral, pulsating, moderate-severe intensity; nausea/vomiting; photophobia/phonophobia; lasts 4–72 hrs; may have aura (visual scotoma, zigzag lines) |
| Tension-Type Headache (TTH) | Bilateral, "band-like" pressure; mild-moderate; no nausea/vomiting; not aggravated by physical activity |
| Cluster Headache | Unilateral, periorbital/temporal; severe, "boring/stabbing"; autonomic features (lacrimation, rhinorrhea, ptosis, miosis); lasts 15–180 min; occurs in clusters |
| Chronic Daily Headache | Headache ≥15 days/month for >3 months |
| Hemicrania Continua | Continuous, unilateral; responsive to indomethacin |
| New Daily Persistent Headache (NDPH) | Daily from onset, no prior headache history |
| Primary Cough/Exertional/Sexual Headache | Triggered by Valsalva, exercise, or sexual activity |
SECONDARY HEADACHE DISORDERS
Per ICHD-3 criteria, a secondary headache develops in temporal relation to an underlying causative disorder (Management of Headache, p. 30).
🔴 EMERGENT / LIFE-THREATENING
| Cause | Key Features |
|---|---|
| Subarachnoid Hemorrhage (SAH) | "Thunderclap" headache — worst headache of life, sudden onset; nuchal rigidity; LP shows xanthochromia |
| Bacterial Meningitis | Fever + headache + neck stiffness + photophobia; Kernig's/Brudzinski's sign positive |
| Hypertensive Emergency | BP >180/120; pulsating headache; papilledema; encephalopathy |
| Cerebral Venous Sinus Thrombosis (CVST) | Progressive headache, seizures, focal deficits; hypercoagulable states |
| Epidural/Subdural Hematoma | Trauma history; lucid interval (epidural); progressive drowsiness |
| Brain Abscess | Fever, focal deficits, raised ICP; subacute onset |
| Acute Angle-Closure Glaucoma | Severe orbital pain; halos around lights; fixed mid-dilated pupil; nausea/vomiting |
⚠️ SERIOUS (URGENT)
| Cause | Key Features |
|---|---|
| Intracranial Tumor | Progressive, worse in morning/lying down, aggravated by Valsalva; focal deficits; papilledema |
| Idiopathic Intracranial Hypertension (IIH) | Obese young women; pulsatile tinnitus; visual changes; papilledema; high CSF opening pressure |
| Temporal (Giant Cell) Arteritis | Age >50; temporal artery tenderness; jaw claudication; elevated ESR/CRP; risk of blindness |
| Carotid/Vertebral Artery Dissection | Neck pain; Horner's syndrome; focal neurological deficits |
| Carbon Monoxide Poisoning | Multiple people affected; exposure history; cherry-red skin |
NON-URGENT SECONDARY CAUSES
| Cause | Key Features |
|---|---|
| Sinusitis | Facial pain/pressure; purulent nasal discharge; tenderness over sinuses |
| Cervicogenic Headache | Neck pain/stiffness; restricted cervical ROM; referred from C1-C3 |
| Post-traumatic Headache | Follows head injury; onset within 7 days |
| Medication Overuse Headache (MOH) | >10–15 days/month analgesic use; rebound headache |
| Viral Meningitis | Self-limited; less toxic than bacterial |
| Hypothyroidism | Diffuse headache; other features of hypothyroidism |
| Sleep Apnea Headache | Morning headaches; improves after waking |
| Dental/TMJ Disorders | Temporal/preauricular pain; aggravated by jaw movement |
| Anemia / Hypoxia | Diffuse; associated systemic features |
| High-Altitude Headache | Recent ascent; resolves with descent/oxygen |
RED FLAGS ("SNOOP4" Mnemonic)
Per Harrison's (p. 572), new-onset severe headache demands urgent evaluation:
| Letter | Feature |
|---|---|
| S | Systemic symptoms (fever, weight loss) or Secondary risk factors (HIV, malignancy) |
| N | Neurological symptoms or signs (confusion, focal deficits, papilledema) |
| O | Onset sudden / thunderclap |
| O | Older age (>50 — think GCA, tumor) |
| P | Progressive headache, or Positional change |
| P | Precipitated by Valsalva/cough/exertion |
| P | Pregnancy or postpartum |
| P | Prior headache history — change in pattern |
Any red flag warrants urgent neuroimaging (CT/MRI) ± LP before attributing to a primary disorder.
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