Paroxysmal hemicrania and cluster headaches are both primary headache disorders that fall under the category of trigeminal autonomic cephalalgias (TACs). They share some similarities—severe unilateral pain and autonomic symptoms—but differ in key features like duration, frequency, and treatment response. Here’s a breakdown:

Paroxysmal Hemicrania (PH)

• What it is: A rare TAC characterized by short, frequent attacks of severe unilateral head pain with autonomic features.
• Symptoms:
  • Pain: Severe, sharp, or throbbing, typically orbital, supraorbital, or temporal, always unilateral.
  • Duration: 2–30 minutes (average ~10–20 minutes).
  • Frequency: 5–40 attacks per day, often >5 daily for more than half the time during active periods.
  • Autonomic signs: Ipsilateral lacrimation, nasal congestion, eyelid edema, conjunctival injection, or ptosis (at least one is usually present).
  • Restlessness or agitation: Less common than in cluster headaches.
• Pattern: Can be chronic (no remission >3 months/year) or episodic (remissions >3 months).
• Triggers: Sometimes neck movement or pressure on trigger points; less often alcohol.
• Demographics: Slightly more common in women (F:M ~2:1), onset typically 20s–40s.
• Diagnosis: Based on ICHD-3 criteria; key is attack brevity and frequency + autonomic symptoms.
• Treatment: Indomethacin is the hallmark—complete response (pain relief within hours to days at 25–300 mg/day) is diagnostic. Alternatives (if indomethacin-intolerant) include COX-2 inhibitors or topiramate, but less effective.

Cluster Headaches (CH)

• What it is: The most common TAC, known for excruciating unilateral pain and a “clustered” pattern of attacks.
• Symptoms:
  • Pain: Extremely severe, boring, or burning, usually orbital, supraorbital, or temporal, strictly unilateral.
  • Duration: 15–180 minutes (average ~45–90 minutes).
  • Frequency: 1–8 attacks per day, often at predictable times (e.g., nocturnal “alarm clock” headaches).
  • Autonomic signs: Similar to PH—lacrimation, nasal congestion, conjunctival injection, etc., on the same side as pain.
  • Restlessness or agitation: Very common (90% of patients), often pacing or rocking during attacks.
• Pattern: Mostly episodic (weeks to months of attacks, then remission for months/years); 10–15% chronic (no remission >3 months).
• Triggers: Alcohol (during clusters), nitroglycerin, strong odors; less tied to mechanical triggers.
• Demographics: More common in men (M:F ~3:1), onset typically 20s–30s, often smokers.
• Diagnosis: ICHD-3 criteria; longer duration and circadian rhythm (e.g., nighttime attacks) are clues.
• Treatment:
  • Acute: High-flow oxygen (100% at 12–15 L/min for 15–20 min) aborts attacks in ~70%; subcutaneous sumatriptan (6 mg) or nasal zolmitriptan.
  • Preventive: Verapamil (240–480 mg/day) is first-line; steroids or lithium for transitional prophylaxis. Indomethacin usually ineffective.

Key Differences

1. Duration: PH attacks are shorter (2–30 min) vs. CH (15–180 min).
2. Frequency: PH is more frequent (>5/day) vs. CH (1–8/day).
3. Treatment Response: PH resolves with indomethacin; CH does not (oxygen/verapamil are key for CH).
4. Restlessness: Prominent in CH, less so in PH.
5. Sex Ratio: PH favors women slightly; CH favors men.
6. Chronicity: PH is more often chronic; CH is usually episodic.

Overlap and Confusion

• Both feature severe unilateral pain with autonomic symptoms (e.g., tearing, nasal stuffiness), making differentiation tough without timing and treatment clues.
• Misdiagnosis can occur—e.g., CH mistaken for PH if attacks are unusually short, or PH missed if indomethacin isn’t trialed.

Practical Approach

• History: Ask about attack length, frequency, and timing (e.g., nocturnal pattern in CH).
• Trial: Indomethacin challenge—response confirms PH; no response leans toward CH.
• Autonomic Features: Present in both, so not a differentiator alone.
• Behavior: Restlessness strongly suggests CH.