What are the common primary and secondary causes of headache?

Common Causes of Headache

Headaches are classified as either primary (migraine, tension-type, cluster) or secondary (resulting from underlying pathology), with primary headaches accounting for the vast majority of cases but secondary causes requiring exclusion when red flags are present. 1

Primary Headache Disorders

Migraine

• Migraine without aura presents as recurrent moderate-to-severe unilateral, pulsating headache lasting 4-72 hours, accompanied by nausea/vomiting and/or photophobia plus phonophobia, worsened by routine physical activity 1, 2
• Migraine with aura includes the above features plus recurrent short-lasting visual, sensory, or speech disturbances that develop gradually over ≥5 minutes and last <60 minutes 2, 3
• Chronic migraine occurs on ≥15 days per month for >3 months, with ≥8 days meeting migraine criteria 1, 2
• Migraine affects approximately 12% of the population and is the second leading cause of years lived with disability worldwide 1, 4

Tension-Type Headache (TTH)

• Presents as bilateral, mild-to-moderate pressing or tightening quality pain that is not aggravated by routine physical activity 1
• Lacks the accompanying symptoms characteristic of migraine (no nausea, no photophobia/phonophobia combination) 1
• Most common primary headache disorder, affecting approximately 38% of the general population 2, 4

Cluster Headache

• Strictly unilateral severe or very severe headache lasting 15-180 minutes 1
• Accompanied by ipsilateral cranial autonomic symptoms including conjunctival injection, lacrimation, nasal congestion, ptosis, or miosis 1
• Affects approximately 0.1% of the population 1, 2

Medication-Overuse Headache (MOH)

• Develops in patients with ≥15 headache days per month who regularly overuse acute medications: non-opioid analgesics on ≥15 days/month OR other acute medications on ≥10 days/month for >3 months 1, 2
• Commonly develops from overuse of medications to treat migraine attacks 1

Secondary Headache Disorders (Red Flags)

Life-Threatening Causes Requiring Immediate Evaluation

Subarachnoid Hemorrhage (SAH)

• Thunderclap headache described as "worst headache of life" with abrupt onset 1, 2
• Non-contrast CT head is the imaging modality of choice if presenting <6 hours from onset (sensitivity 95% on day 0, declining to 74% on day 3) 1, 2

Meningitis

• Headache accompanied by neck stiffness and unexplained fever 1, 2
• Requires immediate evaluation and treatment 2, 5

Brain Tumor/Space-Occupying Lesion

• Progressive headache that awakens patient from sleep or worsens with Valsalva maneuver, coughing, or exertion 2, 6
• Nearly all children with brain tumors have abnormal neurologic findings at diagnosis (94%), with 60% having papilledema 1

Giant Cell Arteritis

• New-onset headache in patients >50 years with scalp tenderness or jaw claudication 2, 5
• ESR/CRP should be checked, though ESR can be normal in 10-36% of cases 2

Other Secondary Causes

Increased Intracranial Pressure

• Headache worsening with coughing, sneezing, or exercise 2, 6

Spontaneous Intracranial Hypotension

• Orthostatic headache: absent or mild on waking, onset within 2 hours of upright posture, >50% improvement within 2 hours of lying flat 2

Stroke/TIA

• Atypical aura with focal neurological symptoms lasting >60 minutes 2, 3

Diagnostic Approach

History and Physical Examination

• Document age at onset (migraine typically begins at/around puberty), duration of episodes, frequency (episodic vs ≥15 days/month), pain location (unilateral vs bilateral), quality (pulsating vs pressing), and severity 2, 5
• Identify aggravating factors (routine activity worsens migraine but not TTH; Valsalva/cough suggests secondary causes) and accompanying symptoms (nausea/vomiting, photophobia, phonophobia for migraine; autonomic symptoms for cluster) 2, 5
• Perform complete neurologic examination including vital signs with blood pressure measurement and examination of optic discs 1

Screening Tools

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

Neuroimaging Indications

Neuroimaging is indicated ONLY when red flags are present or secondary headache is suspected based on history and physical examination 1

• MRI brain with and without contrast is preferred for subacute presentations or suspected tumor/inflammatory processes due to higher resolution and no ionizing radiation 1, 2
• Non-contrast CT head is indicated for acute presentations <6 hours from onset when SAH is suspected, or in acute trauma settings 1, 2
• Neuroimaging in children with primary headaches has very low yield (<1% relevant findings), with most abnormalities being incidental 1

Common Pitfalls

• Misdiagnosing migraine with cranial autonomic symptoms (rhinorrhea occurs in ~62% of pediatric migraineurs) as "sinus headache" 1
• Ordering unnecessary neuroimaging in patients with typical primary headache presentations and normal neurologic examinations 1
• Missing medication-overuse headache by failing to obtain detailed acute medication use history 1, 2
• Overlooking red flags such as new-onset headache after age 50, progressive worsening, atypical aura, or focal neurological symptoms that warrant further investigation 1, 2