Headache

Definition

Headache is pain or discomfort felt in the head, scalp, or neck. It is one of the most common medical symptoms - about 90% of all adults experience headache at some point in their lives, and over 75% of children have complained of headaches by age 15. - Goldman-Cecil Medicine, p. 3809

Classification

The International Classification of Headache Disorders, 3rd edition (ICHD-3) divides headaches into three broad groups:

1. Primary Headache Disorders

These occur on their own, without an identifiable underlying disease. They account for the vast majority of all headaches.

Type	Key Features
Migraine	Moderate-to-severe, unilateral, throbbing; with nausea, vomiting, photophobia, phonophobia; may have aura (visual/sensory disturbances)
Tension-type headache (TTH)	Band-like, bilateral, mild-to-moderate; most common type (60-80% of the population)
Cluster headache	Severe, unilateral, periorbital; occurs in clusters; associated with autonomic features (tearing, ptosis, rhinorrhea)
Trigeminal autonomic cephalalgias (TACs)	Includes paroxysmal hemicrania, SUNA, hemicrania continua
Other primary headaches	Cough headache, exercise headache, sex headache, thunderclap headache, hypnic headache, etc.

2. Secondary Headache Disorders

These result from an identifiable underlying condition. Causes include:

Intracranial: Vascular (subarachnoid hemorrhage, stroke, arteriovenous malformation), infection (meningitis, encephalitis), tumor, cerebrospinal fluid disorders (raised/low ICP)
Extracranial: Sinus disease, dental problems, eye disorders, cervical spine disease
Systemic: Hypertension, metabolic disorders, medication overuse, substance withdrawal, infection

3. Painful Cranial Neuropathies and Other Headaches

Includes trigeminal neuralgia and other facial pain syndromes.

Bradley and Daroff's Neurology in Clinical Practice, ICHD-3 classification

Pathophysiology

Headache pain is initiated by primary trigeminal afferents that innervate blood vessels, mucosa, muscles, and tissues. These fibers converge in the trigeminal ganglion, especially the first (ophthalmic) division. The key pathway is:

Trigeminal afferents → trigeminal ganglion → subnucleus caudalis
Subnucleus caudalis receives input from meningeal vessels, dura, and upper cervical cord
Signals project via the spinothalamic tract to the thalamus, then to the sensory cortex
In primary headaches, chemical mediators such as calcitonin gene-related peptide (CGRP) activate this pathway spontaneously
Cortical spreading depression is thought to underlie migraine aura

The genetic component is well established - familial hemiplegic migraine involves mutations in CACNA1A (calcium channels), ATP1A2 (Na⁺/K⁺-ATPase), and SCN1A (sodium channels). - Goldman-Cecil Medicine, p. 3809

Clinical Features

Pain may be throbbing, band-like, or aching; unilateral or bilateral
Migraine is associated with nausea, vomiting, photophobia, phonophobia
Autonomic features (ptosis, conjunctival injection, tearing, Horner syndrome) occur with cluster headache and TACs
Aura = focal visual, sensory, or motor neurological disturbance preceding or accompanying headache

Red Flags ("SNOOP4" criteria)

Certain features demand urgent evaluation (neuroimaging, etc.):

Thunderclap headache - sudden, severe ("worst headache of my life") - may indicate subarachnoid hemorrhage
New-onset severe headache in a patient with no headache history
Progressive worsening headache - increasing frequency or severity
Headache in a cancer or immunocompromised patient
Associated fever, altered consciousness, or focal neurological deficit
Headache always localized to one area or unresponsive to treatment
Bradley and Daroff's Neurology in Clinical Practice, p. 2082

Diagnosis

Five key history elements (Goldman-Cecil Medicine):

Family history - genetic predisposition
Life history of headache - new vs. longstanding
Attack history - character, duration, frequency, triggers
Medical and psychiatric history - comorbidities
Medication and drug history - medication-overuse headache (MOH)

MRI is the preferred imaging modality when a secondary cause is suspected.

Epidemiology & Burden

Tension-type headache affects 60-80% of the population
Migraine affects ~15% (women 18.3%, men 7.6%)
Cluster headache is rare (~0.1%) but severely disabling
The WHO lists migraine among the top 10 most disabling conditions worldwide
Direct and indirect costs of migraine in the USA exceed $27 billion annually
First-degree relatives of patients with migraine or cluster headache have up to a 4-fold increased risk of the same headache type
Goldman-Cecil Medicine, p. 3809; Frameworks for Internal Medicine, p. 529

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