How are headaches classified and differentiated according to Harrison's?

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Headache Classification and Differentiation According to Harrison's Principles

Primary vs Secondary Classification Framework

Headaches are fundamentally divided into primary disorders (where headache itself is the disease) and secondary disorders (where headache results from underlying pathology), with primary headaches accounting for approximately 90% of presentations and requiring no abnormal findings on neurological examination. 1, 2, 3

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 activity) AND ≥1 associated symptom (nausea/vomiting OR both photophobia and phonophobia) 1, 2
  • Duration in children: Attacks may last 2-72 hours in patients <18 years 4
  • Key differentiating feature: Photophobia together with nausea strongly supports migraine diagnosis 1
  • Prevalence: Affects 18% of women and 6.5% of men in the United States 2

Migraine With Aura

  • Diagnostic requirements: At least 2 attacks with one or more fully reversible aura symptoms (visual, sensory, speech/language, motor, brainstem, or retinal) 4
  • Critical timing characteristics: At least 3 of 6 features must be present: 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), aura accompanied by or followed within 60 minutes by headache 4
  • Duration limits: Acceptable maximal aura duration is 60 minutes per symptom (e.g., 3 symptoms = maximum 180 minutes); motor symptoms may last up to 72 hours 4
  • Red flag: Atypical aura with focal neurological symptoms or duration >60 minutes may indicate stroke or serious intracranial pathology 1

Chronic Migraine

  • Definition: ≥15 headache days/month for >3 months, with ≥8 days meeting migraine criteria 1, 2
  • Management implication: Requires preventive therapy initiation and neurology referral 1

Tension-Type Headache

  • Distinguishing features: Bilateral, mild-to-moderate pressing/tightening quality; NOT aggravated by routine activity; lacks nausea/vomiting AND lacks the combination of photophobia plus phonophobia 1, 2
  • Duration variability: Highly variable, ranging from 30 minutes to 7 days, often briefer than migraine's 4-72 hour duration 5
  • Prevalence: Most common primary headache disorder, affecting approximately 38% of the general population 1, 3
  • Chronic form treatment: Amitriptyline is first-line preventive therapy for chronic tension-type headache 1

Cluster Headache

  • Pathognomonic features: Strictly unilateral severe headache lasting 15-180 minutes with ipsilateral autonomic symptoms (lacrimation, conjunctival injection, nasal congestion, ptosis, miosis) 1, 2
  • Frequency requirement: 1-8 attacks per day, requiring five attacks for diagnosis 2, 6
  • Prevalence: Affects approximately 0.1% of the general population 1, 2
  • Acute treatment: High-flow oxygen (100% at 12-15 L/min) is first-line; subcutaneous or intranasal triptans are alternatives 1

Trigeminal Autonomic Cephalalgias (TACs)

  • Paroxysmal hemicrania: Shorter duration and higher frequency than cluster headache; responsive to indomethacin 6
  • SUNCT/SUNA: Shortest duration and highest frequency TAC; attacks can occur over 100 times daily 6
  • Hemicrania continua: Continuous headache by definition responsive to indomethacin 6

Secondary Headache Disorders (Red Flag Presentations)

Life-Threatening Emergencies Requiring Immediate Evaluation

  • Subarachnoid hemorrhage: Thunderclap headache ("worst headache of life"), may have altered taste sensation 1
  • Meningitis: Headache with neck stiffness and unexplained fever—requires immediate evaluation 1, 2
  • Brain tumor/space-occupying lesion: Progressive headache, awakens from sleep, worsens with Valsalva/cough 1
  • Giant cell arteritis: New-onset headache in patients >50 years with scalp tenderness, jaw claudication; note ESR can be normal in 10-36% of cases 1
  • Stroke/TIA: Atypical aura with focal neurological symptoms 1

Other Secondary Causes

  • Increased intracranial pressure: Headache worsening with coughing, sneezing, exercise 1
  • Medication-overuse headache: ≥15 headache days/month with regular overuse of non-opioid analgesics ≥15 days/month OR other acute medications ≥10 days/month for >3 months 1, 5
  • Spontaneous intracranial hypotension: Orthostatic headache (absent/mild on waking, onset within 2 hours of upright posture, >50% improvement within 2 hours of lying flat) 1

Diagnostic Approach Algorithm

Step 1: Screen for Red Flags (Emergency Admission if Present)

  • Thunderclap headache, new-onset after age 50, progressive worsening, atypical aura, recent head/neck trauma, awakening from sleep, Valsalva/cough/exertion provocation, focal neurological symptoms/signs, unexplained fever, neck stiffness, altered consciousness/memory/personality, witnessed loss of consciousness 1, 2

Step 2: Characterize Pain Pattern

  • Duration: Migraine 4-72 hours; cluster 15-180 minutes; tension-type variable (30 minutes to 7 days) 1, 5
  • Location: Unilateral (migraine, cluster) vs bilateral (tension-type) 1
  • Quality: Pulsating (migraine) vs pressing/tightening (tension-type) vs severe unilateral (cluster) 1
  • Severity: Moderate-to-severe (migraine, cluster) vs mild-to-moderate (tension-type) 1

Step 3: Identify Associated Symptoms

  • Migraine: Nausea/vomiting, photophobia AND phonophobia, aggravation by routine activity 1, 2
  • Cluster: Ipsilateral autonomic symptoms (lacrimation, conjunctival injection, nasal congestion, ptosis, miosis) 1, 6
  • Tension-type: Lacks prominent associated symptoms 2

Step 4: Use Validated Screening Tools

  • ID-Migraine questionnaire (3-item): Sensitivity 0.81, specificity 0.75, positive predictive value 0.93 1
  • Migraine Screen Questionnaire (5-item): Sensitivity 0.93, specificity 0.81, positive predictive value 0.83 1
  • Headache diary: Document frequency, duration, character, triggers, accompanying symptoms, medication use to reduce recall bias and increase diagnostic accuracy 1, 2

Step 5: Neuroimaging Decision

  • NOT indicated: Normal neurological examination without red flags yields only 0.2% probability of serious intracranial pathology (no higher than 0.4% in asymptomatic volunteers) 1
  • MRI brain with/without contrast: Preferred modality for subacute presentations or suspected tumor/inflammatory process 1, 2
  • Non-contrast CT head: If presenting <6 hours from acute severe headache onset (subarachnoid hemorrhage); sensitivity 95% on day 0,74% on day 3,50% at 1 week 1

Common Diagnostic Pitfalls

  • Do not misdiagnose Computer Vision Syndrome as migraine: Blurred vision in CVS stems from accommodative strain, not migraine aura; headache is bilateral, dull, pressing, and improves when screen exposure stops 5
  • Do not overlook medication-overuse headache: Regular overuse of acute medications can transform episodic migraine into chronic daily headache 1, 5
  • Do not order unnecessary neuroimaging: In patients with normal examinations and clear primary headache patterns, diagnostic yield is only ~0.2% 1, 5
  • Do not assume normal ESR excludes giant cell arteritis: ESR can be normal in 10-36% of cases 1
  • Recognize that a single patient can have multiple headache types simultaneously: The International Headache Society classification diagnoses syndromes, not patients 2

Referral Pathways

  • Emergency admission: Any red flag present, patient unable to self-care without help 1
  • Urgent neurology referral (within 48 hours): Suspected spontaneous intracranial hypotension, patient unable to self-care but has help 1
  • Routine neurology referral (2-4 weeks): Suspected primary headache disorder, diagnosis uncertain, first-line treatments fail 1
  • Rheumatology referral: Suspected giant cell arteritis 1

References

1
Guideline

Approach to Assessment of Headache

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

2
Guideline

Headache Classification and Diagnosis

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

4
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

5
Guideline

Management of Computer Vision Syndrome–Associated Tension‑Type Headache

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

6
Research

Trigeminal autonomic cephalalgias.

Oral diseases, 2016

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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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