What are the primary and secondary headache types in Harrison's classification and how are they distinguished?

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Differentiation of Headache Types Based on Harrison's Principles

Primary vs. Secondary Headache Classification

Headaches are fundamentally divided into primary disorders (where the headache itself is the disease) and secondary disorders (where headache results from an underlying pathology). 1, 2

Primary Headache Disorders

Migraine Without Aura

  • Diagnostic requirements: At least 5 lifetime attacks lasting 4–72 hours (untreated), with ≥2 pain characteristics (unilateral location, pulsating quality, moderate-to-severe intensity, or aggravation by routine physical activity) AND ≥1 associated symptom (nausea/vomiting OR both photophobia and phonophobia). 3, 1
  • Key distinguishing features: The combination of photophobia with nausea strongly supports migraine over other primary headaches. 1
  • Pediatric variation: In children <18 years, attacks may last only 2–72 hours and are often bilateral rather than unilateral. 3, 4

Migraine With Aura

  • Diagnostic requirements: At least 2 attacks with fully reversible visual, sensory, speech/language, motor, brainstem, or retinal symptoms, plus ≥3 of the following: gradual spread over ≥5 minutes, two or more symptoms in succession, individual symptom duration 5–60 minutes, at least one unilateral symptom, at least one positive symptom (scintillations, pins and needles), and aura accompanied by or followed by headache within 60 minutes. 3, 1
  • Critical distinction: Atypical aura lasting >60 minutes or with focal neurological deficits is a red flag for stroke or other serious pathology, not typical migraine. 1, 5

Chronic Migraine

  • Definition: ≥15 headache days per month for >3 months, with ≥8 days meeting migraine criteria. 1, 5
  • Management implication: This represents a distinct entity requiring preventive therapy and neurology referral, not simply frequent episodic migraine. 1, 5

Tension-Type Headache

  • Characteristic features: Bilateral, mild-to-moderate pressing or tightening quality, NOT aggravated by routine physical activity, and lacks both nausea/vomiting AND the combination of photophobia plus phonophobia. 3, 1
  • Duration variability: Episodes range from 30 minutes to 7 days, much more variable than the 4–72 hour migraine window. 1
  • Prevalence: Affects approximately 38% of the general population, making it the most common primary headache disorder. 1

Cluster Headache

  • Defining characteristics: Strictly unilateral severe or very severe headache lasting 15–180 minutes, with ipsilateral cranial autonomic symptoms (conjunctival injection, lacrimation, nasal congestion, ptosis, miosis). 3, 1
  • Prevalence: Affects only ~0.1% of the population. 3, 1
  • Acute treatment: High-flow oxygen (100% at 12–15 L/min) or subcutaneous/intranasal triptans are first-line. 1

Secondary Headache Disorders

Life-Threatening Causes Requiring Immediate Recognition

Subarachnoid Hemorrhage

  • Presentation: Thunderclap headache ("worst headache of life"), may have altered taste sensation. 1, 5
  • Imaging urgency: Non-contrast CT within 6 hours has 95% sensitivity; this drops to 74% by day 3 and 50% at 1 week. 5

Meningitis

  • Red flags: Headache with neck stiffness and unexplained fever. 3, 1, 5
  • Action required: Immediate evaluation and lumbar puncture after neuroimaging if indicated. 1

Brain Tumor/Space-Occupying Lesion

  • Presentation pattern: Progressive headache worsening over weeks to months, awakens patient from sleep, worsens with Valsalva/cough. 1, 5
  • Pediatric data: 94% of children with brain tumors have abnormal neurological findings at diagnosis; 60% have papilledema. 5, 4

Giant Cell Arteritis

  • Clinical context: New-onset headache in patients >50 years with scalp tenderness, jaw claudication. 1
  • Laboratory caveat: ESR can be normal in 10–36% of cases. 1

Other Important Secondary Causes

Medication-Overuse Headache

  • Diagnostic criteria: ≥15 headache days per month with regular overuse of acute medications (non-opioid analgesics ≥15 days/month OR other acute medications ≥10 days/month) for >3 months. 3, 1, 5
  • Clinical significance: Often conflated with chronic migraine but represents a distinct secondary disorder requiring different management. 3

Spontaneous Intracranial Hypotension

  • Pathognomonic feature: Orthostatic headache—absent or mild on waking, onset within 2 hours of upright posture, >50% improvement within 2 hours of lying flat. 1

Systematic Diagnostic Approach

History-Taking Algorithm

  1. Temporal pattern:

    • Episodic vs. chronic (≥15 days/month for >3 months) 1, 5
    • Duration per episode: 15–180 min (cluster), 4–72 h (migraine), 30 min–7 days (tension-type) 3, 1

  2. Pain characteristics:

    • Location: Unilateral (migraine, cluster) vs. bilateral (tension-type) 3, 1
    • Quality: Pulsating (migraine) vs. pressing/tightening (tension-type) vs. severe unilateral (cluster) 3, 1
    • Intensity: Moderate-to-severe (migraine, cluster) vs. mild-to-moderate (tension-type) 3, 1

  3. Aggravating/relieving factors:

    • Routine activity worsens migraine but NOT tension-type 3, 1
    • Valsalva/cough suggests increased intracranial pressure 1, 5
    • Lying flat improves orthostatic headache 1

  4. Associated symptoms:

    • Nausea/vomiting, photophobia, phonophobia → migraine 3, 1
    • Ipsilateral autonomic symptoms → cluster 3, 1
    • Absence of associated symptoms → tension-type 3, 1

Red Flags Mandating Further Investigation

  • Thunderclap headache 1, 5
  • New-onset headache after age 50 1, 5
  • Progressive worsening over weeks to months 1, 5
  • Atypical aura (>60 minutes or focal deficits) 1, 5
  • Recent head/neck trauma 1
  • Awakens patient from sleep 1
  • Unexplained fever with neck stiffness 3, 1, 5
  • Focal neurological symptoms/signs 3, 1, 5
  • Papilledema on fundoscopy 5, 4
  • Altered consciousness, memory, or personality 1

Physical Examination Priorities

  • Vital signs including blood pressure (hypertension may indicate increased intracranial pressure) 3, 4
  • Complete neurological examination including cranial nerves, motor/sensory testing, cerebellar function, gait 3, 4
  • Fundoscopic examination (papilledema present in ~60% of pediatric brain tumors) 5, 4
  • Neck examination (stiffness, limited flexion) 1

Diagnostic Tools and Investigations

Screening Instruments

  • ID-Migraine (3-item): Sensitivity 0.81, specificity 0.75, positive predictive value 0.93 3, 1, 5
  • Migraine Screen Questionnaire (5-item): Sensitivity 0.93, specificity 0.81, positive predictive value 0.83 3, 1, 5
  • Headache diary: Documents frequency, duration, triggers, accompanying symptoms, medication use; reduces recall bias and increases diagnostic accuracy 1, 5

Neuroimaging Indications

Neuroimaging is NOT indicated for primary headaches with normal neurological examination and no red flags—the yield is <1% for clinically significant findings. 3, 1, 5, 4

When Imaging IS Required:

  • Emergent non-contrast CT: Thunderclap headache presenting within 6 hours 1, 5, 4
  • MRI with and without contrast (preferred): Any abnormal neurological finding, progressive headache pattern, new-onset after age 50, atypical aura, suspected tumor/inflammatory/posterior-fossa pathology 1, 5, 4
  • MRV: Suspected venous sinus thrombosis (especially with mastoiditis or sphenoid sinusitis) 4

Common Pitfalls and How to Avoid Them

Pitfall 1: Conflating Chronic Migraine with Medication-Overuse Headache

  • Solution: Both can coexist; systematically document medication frequency (≥10 days/month for triptans/opioids, ≥15 days/month for simple analgesics). 3, 1

Pitfall 2: Ordering Neuroimaging Without Red Flags

  • Solution: In patients with normal examination and no red flags, imaging likelihood of significant pathology is <1%—reassure and treat the primary headache disorder. 3, 1, 5, 4

Pitfall 3: Misdiagnosing Pediatric Migraine as "Sinus Headache"

  • Solution: Cranial autonomic symptoms (rhinorrhea, nasal congestion) occur in ~62% of pediatric migraineurs; consider migraine first. 5, 4

Pitfall 4: Missing Giant Cell Arteritis in Older Adults

  • Solution: Any new-onset headache after age 50 requires ESR/CRP, but remember ESR can be normal in 10–36% of cases. 1

Pitfall 5: Dismissing Occipital Headache in Children

  • Solution: Occipital location is rare in children and warrants caution for posterior-fossa pathology or Chiari malformation. 5, 4

References

1
Guideline

Approach to Assessment of Headache

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

3
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

4
Guideline

Neurological Examination for Severe Headache in Pediatric Patients

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

5
Guideline

Headache Red Flags, Imaging Recommendations, and Pediatric Considerations

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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