Headache

Definition

A headache is pain or discomfort felt in the region of the head, scalp, or neck. Importantly, the brain parenchyma itself is insensitive to pain. The pain-sensitive structures in the head include the meninges, the arteries and veins supplying the brain, and the tissues lining the cavities within the skull. Much of the pain - especially in vascular headaches and migraines - is mediated through the fifth cranial nerve (trigeminal nerve, CNV). Pain from inflammation in a specific structure (e.g., sinusitis, abscess) is easier to localize, while tension and traction headaches tend to produce more diffuse, harder-to-localize pain.

ROSEN's Emergency Medicine, p. 3988

Classification: Primary vs. Secondary

The International Headache Society (IHS) publishes the International Classification of Headache Disorders (ICHD-3), which divides headaches into two broad categories:

1. Primary Headaches

No underlying structural or medical cause - the headache itself is the disorder.

Migraine (with or without aura)
Tension-type headache
Cluster headache and other trigeminal autonomic cephalalgias

2. Secondary Headaches

Caused by an identifiable underlying condition, such as:

Subarachnoid hemorrhage (SAH) / intracranial hemorrhage
Meningitis
Cerebral venous sinus thrombosis
Idiopathic intracranial hypertension (IIH)
Space-occupying lesions (tumors)
Carbon monoxide poisoning
Temporal arteritis
Acute angle-closure glaucoma
Cervical artery dissection
ROSEN's Emergency Medicine, p. 3981-3983

Major Types of Primary Headache

Tension-Type Headache (most common)

Character: Mild-to-moderate, pressing/tightening (not pulsating), bilateral, holocranial
Associated features: No nausea/vomiting; photophobia or phonophobia may be present, but not both
Does not worsen with physical activity
More common in women; higher prevalence in Western countries
Treatment: Acetaminophen or NSAIDs for acute episodes; amitriptyline for chronic prevention
Goldman-Cecil Medicine, p. 3817

Migraine

Character: Moderate-to-severe pulsating pain, typically unilateral (frontoparietal), lasting 4-24 hours
Associated features: Nausea, vomiting, photophobia, phonophobia
Worsens with routine physical activity
More common in women; often starts in adolescence/young adulthood
May come with an aura (transient neurological symptoms - visual disturbances, sensory changes)
Treatment (acute): Triptans, ergotamine, NSAIDs; Prevention: propranolol, amitriptyline, valproate
Adams and Victor's Principles of Neurology

Cluster Headache

Character: Severe, unilateral, periorbital/temporal, described as "boring" or "stabbing"
Duration: 15 minutes to 3 hours; typically nocturnal (1-2 hours after falling asleep)
Associated features: Ipsilateral lacrimation, rhinorrhea, ptosis, conjunctival injection (autonomic features)
Predominantly affects males (3:1 to 7:1); onset usually ages 20-30
Occurs in "clusters" - nightly attacks for weeks to months, then remission
Treatment: Oxygen, sumatriptan, ergotamine
Goldman-Cecil Medicine, p. 3859

Red Flag Features ("SNOOP4" warning signs)

When these features are present, a serious underlying cause must be ruled out and neuroimaging is required:

Red Flag	Concern
Thunderclap onset - "worst headache of life"	Subarachnoid hemorrhage
New onset in age >50	Temporal arteritis, mass lesion
Progressive worsening in frequency/severity	Mass lesion, chronic meningitis
Fever, altered mental status, nuchal rigidity	Meningitis, encephalitis
Focal neurological deficit	Stroke, mass lesion
Headache in a cancer patient	Brain metastasis
Always localized to one side	Mass, AVM
Postural component (worse lying down)	Raised intracranial pressure

Bradley and Daroff's Neurology, p. 2082

Epidemiology

Headache is one of the top reasons for emergency department visits. The vast majority of patients presenting with headache have a benign primary cause (tension or migraine). However, life-threatening causes - most commonly SAH - are missed more than 25% of the time on first presentation, making careful assessment critical.

Summary

Feature	Tension	Migraine	Cluster
Location	Bilateral, diffuse	Unilateral	Unilateral (orbital)
Quality	Pressing/tight	Pulsating	Stabbing/boring
Severity	Mild-moderate	Moderate-severe	Severe (excruciating)
Nausea/vomiting	No	Yes	Sometimes
Autonomic features	No	No	Yes (ipsilateral)
Duration	30 min - 7 days	4-72 hours	15 min - 3 hours
Sex predominance	Female	Female	Male

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