Distinguishing Migraine from Hemicrania Continua
The critical distinguishing feature is the temporal pattern: hemicrania continua presents as a continuous, unrelenting unilateral headache with fluctuating intensity, whereas migraine occurs in discrete episodic attacks lasting 4-72 hours with pain-free intervals between episodes.
Key Diagnostic Algorithm
Step 1: Assess Temporal Pattern (Most Critical)
Hemicrania Continua:
- Continuous daily headache without pain-free periods
- Background pain present 24/7 (typically moderate intensity, rated 6.5/10) 1
- Superimposed severe exacerbations (rated 9/10, often excruciating) 1
- 82% present with chronic unremitting form from onset 1
Migraine:
- Episodic attacks lasting 4-72 hours when untreated 2
- Complete pain-free intervals between attacks
- Requires ≥5 attacks meeting diagnostic criteria 2
Step 2: Evaluate Pain Characteristics
Hemicrania Continua:
- Strictly unilateral and side-locked in 92% of cases 1
- Never switches sides during an attack
- Continuous baseline pain with exacerbations 1
Migraine:
- Can be unilateral OR bilateral 2
- May switch sides between attacks
- Pulsating quality typical 2
- Aggravated by routine physical activity 2
Step 3: Identify Cranial Autonomic Features
Hemicrania Continua:
- Present in 74-97% during exacerbations 1, 3
- Lacrimation (73%), nasal congestion (51%), conjunctival injection (46%), ptosis (40%) 1
- Critical caveat: Absence of autonomic features does NOT exclude hemicrania continua 4
Migraine:
- Cranial autonomic symptoms uncommon
- When present, typically mild and not prominent
Step 4: Check for Migrainous Features (Potential Pitfall)
Major diagnostic trap: 70.6% of hemicrania continua patients meet IHS criteria for migraine during their exacerbation periods 3. Both conditions can have:
- Photophobia (74% in HC) 1
- Phonophobia (79% in HC) 1
- Nausea (69% in HC) 1
- Motion sensitivity (69% in HC) 1
The presence of migrainous features does NOT exclude hemicrania continua.
Step 5: Perform Indomethacin Trial (Definitive Test)
This is the sine qua non for hemicrania continua 1, 3, 5:
Indomethacin test protocol:
- Oral: 75 mg twice daily for 3 days 6
- Injectable: 100-200 mg intramuscularly 1
- Typical maintenance dose: 136.7 ± 60 mg daily (range 25-225 mg) 3
Expected response:
- Hemicrania continua: Complete (absolute) response within days 1, 5
- Migraine: No response or minimal/incomplete response 4
Critical recommendation: An indomethacin trial should be performed for ANY patient with unilateral pain, with or without cranial autonomic symptoms 1.
Common Diagnostic Pitfalls
Focusing only on exacerbations: Physicians and patients often overlook the persistent background headache, leading to misdiagnosis as episodic migraine 7
Migrainous features mislead: The presence of nausea, photophobia, and phonophobia causes misdiagnosis as migraine in the majority of cases 3, 7
Assuming autonomic features are required: While common, their absence doesn't exclude hemicrania continua 4
Missing the remitting subtype: 11.8% have episodic patterns with pain-free remissions lasting months, mimicking cluster headache 1, 8
Clinical Decision Points
Suspect hemicrania continua when:
- Unilateral headache is present daily without complete pain-free periods
- Patient describes "always there" background pain with worse episodes
- Strictly side-locked pain (never switches sides)
- Previous migraine treatments have failed
- Occipital tenderness present (67.6% of cases) 3
Suspect migraine when:
- Clear episodic pattern with complete pain-free intervals
- Attacks last 4-72 hours
- Bilateral or alternating-side headaches
- Pulsating quality with activity aggravation
- Family history of migraine 2
When uncertain: Proceed directly to indomethacin trial, as this provides definitive differentiation and hemicrania continua is commonly misdiagnosed even by specialists 7. The response is dramatic and unmistakable in true hemicrania continua 4, 5.