Headache: What Could Be Causing It?

How Common Is Headache and Why Does It Happen?

Headache is among the most common reasons adults seek medical care. A 2022 systematic review in the Journal of Headache and Pain estimated the global prevalence of active headache disorder at 52.0%, with tension-type headache accounting for 42.0% and migraine for 14.0% of all cases worldwide 1. That single statistic reframes the clinical question: for the majority of patients, headache reflects a primary disorder of pain processing or muscle tension rather than structural disease.

Pain in the head originates from pain-sensitive structures: blood vessels, meninges, periosteal tissue, muscles of the scalp and neck, and cranial nerves V, IX, and X. The brain parenchyma itself lacks nociceptors. Understanding which structure is generating pain helps separate primary from secondary headache and guides workup.

Primary vs. Secondary Headache

The International Headache Society's ICHD-3 classification divides headaches into two broad groups 2:

• Primary headaches (tension-type, migraine, cluster, trigeminal autonomic cephalalgias) arise from the pain-processing system itself. No underlying lesion drives them.
• Secondary headaches are caused by another condition, infection, vascular catastrophe, intracranial hypertension, medication overuse, or systemic disease.

The clinical job is to rule out secondary causes first, then classify the primary disorder.

Tension-Type Headache: The Most Common Cause

Tension-type headache (TTH) is bilateral, pressing or tightening in quality, mild-to-moderate in intensity, and not aggravated by routine physical activity. Phonophobia or photophobia may occur, but not both simultaneously, and nausea is absent. These criteria come directly from the ICHD-3 2.

What Triggers It?

Common triggers include sleep deprivation, prolonged screen time, cervical muscle tension, psychological stress, and dehydration. A 2021 cohort study published in Cephalalgia (N=412) found that poor sleep quality predicted TTH frequency more strongly than psychological distress alone 3.

How Is It Treated?

For episodic TTH (fewer than 15 headache days per month), first-line treatment is ibuprofen 400 mg or acetaminophen 1,000 mg taken at headache onset. A Cochrane review of 18 RCTs found ibuprofen 400 mg produced headache relief at 2 hours in 56 to 70% of participants versus 25 to 32% with placebo 4.

Chronic TTH (15 or more days per month for over 3 months) responds to amitriptyline 10 to 75 mg nightly as first-line prevention, based on a double-blind RCT (N=170) published in Neurology 5.

Migraine: A Neurological Disease, Not Just a Bad Headache

Migraine affects approximately 1 billion people globally. The Global Burden of Disease 2019 study ranked migraine as the second leading cause of disability-adjusted life years among neurological conditions 6. It is unilateral, pulsating, moderate-to-severe in intensity, worsened by routine activity, and accompanied by nausea, photophobia, or phonophobia.

Migraine With Aura vs. Without

About 30% of people with migraine experience aura: reversible focal neurological symptoms (visual scotoma, paresthesia, speech disturbance) developing over 5 to 20 minutes and lasting under 60 minutes before the headache phase. Migraine with aura carries a modestly elevated stroke risk, particularly in women who smoke and use combined oral contraceptives, a combination the American Headache Society advises against 7.

Abortive Migraine Treatment

Triptans remain the most evidence-supported class for moderate-to-severe migraine attacks. Sumatriptan 50 to 100 mg oral achieves pain freedom at 2 hours in 28 to 40% of attacks versus 8 to 12% with placebo, based on a Cochrane meta-analysis of 52 RCTs (N=24,516) 8. Sumatriptan 6 mg subcutaneous acts faster, with pain freedom at 1 hour in approximately 55% of patients.

For patients who cannot tolerate or do not respond to triptans, lasmiditan (a 5-HT1F agonist) and rimegepant (a CGRP receptor antagonist) are FDA-approved alternatives 9.

When to Start Migraine Prevention

The American Headache Society recommends preventive therapy when migraine occurs on 4 or more days per month, when attacks are severely disabling, or when acute medications are overused 10. First-line preventives include topiramate 50 to 100 mg/day, propranolol 80 to 240 mg/day, and amitriptyline 25 to 75 mg nightly. CGRP monoclonal antibodies (erenumab, fremanezumab, galcanezumab) offer monthly or quarterly subcutaneous dosing and have each demonstrated 50% responder rates of 40 to 50% in Phase 3 trials 11.

Cluster Headache: Severe, Unilateral, and Cyclical

Cluster headache is comparatively rare (prevalence ~0.1%) but produces arguably the most intense pain of any primary headache disorder. Attacks last 15 to 180 minutes, occur up to 8 times daily, and are strictly unilateral around or behind the eye. Ipsilateral autonomic features (lacrimation, conjunctival injection, nasal congestion, ptosis, or miosis) are required for diagnosis 2.

Acute Treatment

High-flow oxygen at 12 to 15 L/min via non-rebreather mask for 15 to 20 minutes aborts attacks in 78% of patients compared with 20% on air (P<0.001), based on a 2009 RCT in JAMA (N=109) 12. Sumatriptan 6 mg subcutaneous is the pharmacological standard for acute attacks.

Prevention During a Cluster Period

Verapamil 240 to 960 mg/day is first-line preventive therapy. Transitional prevention with a short oral corticosteroid taper (prednisone 60 mg tapered over 2 to 3 weeks) can break an active cluster period while verapamil reaches therapeutic levels 13.

Secondary Headache Causes That Must Not Be Missed

Most headaches are benign. A small but critical proportion are not. The following causes require prompt evaluation.

Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) classically presents as a thunderclap headache: maximum intensity within 1 minute. The sensitivity of non-contrast CT within 6 hours of onset reaches 98.7% for SAH, based on a prospective cohort study (N=3,132) published in BMJ 14. If CT is negative and clinical suspicion remains high, lumbar puncture or CT angiography is indicated.

Meningitis and Encephalitis

Bacterial meningitis presents with headache, fever, neck stiffness, and photophobia. The clinical triad of fever, neck stiffness, and altered mental status has a sensitivity of only 44% for bacterial meningitis, meaning absence of any one feature does not rule it out 15. Blood cultures and immediate empirical antibiotics (ceftriaxone 2 g IV every 12 hours plus vancomycin) should not wait for lumbar puncture results when bacterial meningitis is suspected.

Idiopathic Intracranial Hypertension

Idiopathic intracranial hypertension (IIH) produces daily headache, pulsatile tinnitus, and transient visual obscurations in patients who are most commonly women with obesity aged 20 to 45. Opening pressure on lumbar puncture exceeds 25 cmH2O. The IIH Treatment Trial (N=165) found that acetazolamide 500 to 4,000 mg/day combined with a low-sodium weight-reduction diet improved visual field mean deviation significantly versus diet alone at 6 months (P<0.001) 16.

Giant Cell Arteritis

Giant cell arteritis (GCA) must be considered in any patient over 50 with new-onset headache, jaw claudication, scalp tenderness, or elevated ESR/CRP. Visual loss occurs in approximately 20% of untreated cases. Oral prednisolone 40 to 60 mg/day should begin immediately upon clinical suspicion, before biopsy results return, to protect vision 17.

Cervicogenic Headache

Cervicogenic headache originates from cervical spine structures (C1, C3) and refers pain to the head. It is unilateral, non-throbbing, worsened by neck movement, and associated with restricted cervical range of motion. A 2010 RCT (N=200) published in Spine found cervical manipulation combined with supervised exercise reduced headache frequency and intensity more effectively than either treatment alone at 12 weeks 18.

Medication Overuse Headache

Medication overuse headache (MOH) develops when acute headache medications are used on 10 or more days per month (triptans, ergotamines, combination analgesics) or 15 or more days per month (simple analgesics) for over 3 months. MOH affects approximately 1 to 2% of the global population and is the third most common headache disorder worldwide 19. Treatment requires supervised analgesic withdrawal; multidisciplinary programs achieve sustained remission in 50 to 70% of patients at 1 year.

Red Flags That Require Urgent Evaluation

The following warning signs, sometimes abbreviated as "SNOOP4" in clinical education, indicate a headache that may have a dangerous secondary cause. Any one of them warrants same-day or emergency evaluation.

| Red Flag | Possible Cause | |---|---| | Thunderclap onset (maximal pain within 60 seconds) | Subarachnoid hemorrhage, cerebral venous thrombosis | | New headache after age 50 | Giant cell arteritis, intracranial mass | | Fever plus neck stiffness | Meningitis, encephalitis | | Focal neurological deficit or altered consciousness | Stroke, abscess, mass lesion | | Headache worsened by Valsalva (cough, straining) | Chiari malformation, intracranial hypertension | | Progressive worsening over days to weeks | Subdural hematoma, mass, IIH | | New headache in HIV-positive or immunocompromised patient | CNS opportunistic infection (cryptococcal meningitis) | | Postural component (worse lying flat, better sitting) | Spontaneous intracranial hypotension |

The Neurology clinical practice guideline on headache neuroimaging (2019) states: "Neuroimaging is recommended for patients with headache and unexplained abnormal findings on neurological examination." 20

How Headache Is Diagnosed

Diagnosis is primarily clinical. A structured history covering headache onset, location, quality, severity (0 to 10 numeric rating), duration, frequency, associated symptoms, triggers, and prior treatments establishes the diagnosis in most cases without imaging.

The Role of Neuroimaging

Routine CT or MRI for patients with stable, typical primary headache patterns has a diagnostic yield of approximately 1 to 3% for significant findings, based on a systematic review of 14 studies (N=1,825) 21. Imaging is not recommended for patients meeting ICHD-3 criteria for migraine or TTH who have a normal neurological examination and no red flags.

Laboratory and Lumbar Puncture

ESR and CRP are first-line tests when GCA is suspected. Lumbar puncture is indicated when CT is negative but SAH or meningitis remains clinically possible. Opening pressure measurement during LP is essential when IIH is on the differential.

Headache Diaries

A headache diary tracking dates, duration, severity, triggers, and acute medication use over 4 to 8 weeks provides objective data that changes management in a significant proportion of patients, particularly for identifying MOH and qualifying patients for preventive therapy 22.

Hormonal and Systemic Causes of Headache

Menstrual Migraine

Migraine without aura occurs exclusively around menstruation in approximately 7 to 14% of women with migraine (pure menstrual migraine) and is perimenstrually triggered in up to 60% (menstrually related migraine). The estrogen withdrawal that precedes menstruation appears to be the dominant mechanism. Frovatriptan 2.5 mg twice daily as short-term prevention during the perimenstrual window reduces migraine incidence versus placebo (P<0.001) in a trial (N=546) reported in Cephalalgia 23.

Hypertensive Headache

Severe hypertension (systolic blood pressure above 180 mmHg) can produce occipital headache, but hypertension alone does not commonly cause headache at lower pressures. The association between mild-to-moderate hypertension and headache is not reliably established in the literature 24.

Hypothyroidism

Hypothyroidism is an underrecognized cause of new-onset daily headache. A prospective study (N=102) found that levothyroxine replacement to euthyroid state resolved headache in 30% of patients with hypothyroid-associated headache within 3 months 25.

Evidence-Based Treatment Summary

Treatment selection depends entirely on headache type, frequency, and severity.

Acute Treatment Options by Headache Type

| Headache Type | First-Line Acute Treatment | Dose | |---|---|---| | Tension-type (episodic) | Ibuprofen or acetaminophen | Ibuprofen 400 mg; acetaminophen 1,000 mg | | Migraine (mild-moderate) | NSAIDs or acetaminophen | Naproxen 500 to 825 mg | | Migraine (moderate-severe) | Sumatriptan oral or SC | 50 to 100 mg oral; 6 mg SC | | Cluster (acute attack) | Oxygen + sumatriptan SC | O2 12 to 15 L/min; sumatriptan 6 mg SC | | Medication overuse headache | Withdrawal + bridge therapy | Supervised taper; naproxen bridge |

Preventive Therapy Options for Migraine

Topiramate 100 mg/day reduced monthly migraine days by 2.1 versus 0.5 for placebo (P<0.001) in the MIGR-002 trial (N=487) 26. Propranolol LA 160 mg/day achieves equivalent efficacy with a different side-effect profile, making it preferred in patients with comorbid anxiety or cardiovascular indications.

The American Headache Society 2021 position statement specifies: "CGRP pathway-targeting therapies are appropriate first-line preventive options for episodic and chronic migraine and should not be reserved solely for patients who have failed other preventives." 10

Lifestyle Factors That Modify Headache Frequency

Sleep regularity, hydration, caffeine intake, and stress management each have documented effects on headache burden. A randomized trial (N=232) found that aerobic exercise (40 minutes, 3 times weekly for 12 weeks) reduced migraine days by 0.93 per month, comparable to topiramate 100 mg and relaxation therapy in that three-arm trial (P=0.709 between groups) 27.

Caffeine presents a dual problem: acute caffeine use relieves headache, but daily consumption above 200 mg creates withdrawal headache on missed days. Patients using caffeine-containing analgesics more than 10 days per month should consider a gradual taper.