Causes of Continuous 24/7 Headache
The most critical causes to rule out immediately are medication overuse headache (MOH), chronic migraine, and secondary headaches requiring neuroimaging—particularly in patients with red flag symptoms such as new onset in older adults, progressive worsening, or abnormal neurologic findings.
Primary Differential Diagnosis
Medication Overuse Headache (MOH)
MOH is the most common cause of continuous daily headache and must be considered first 1. This condition develops when patients regularly overuse acute headache medications for more than 3 months:
- Culprit medications: Triptans, ergotamine, opiates, NSAIDs (≥15 days/month), or combination analgesics (≥10 days/month) 2, 1
- Key feature: Headache occurs ≥15 days per month in someone with pre-existing headache disorder 1
- Management: Abrupt withdrawal of the overused medication is the only remedy (except for opioids, which require gradual taper) 1
Chronic Migraine
If MOH is ruled out, chronic migraine is the next consideration 1:
- Diagnostic criteria: ≥15 headache days per month for >3 months, with ≥8 days meeting migraine criteria 1
- Risk factors: Female sex, high baseline headache frequency, inadequate treatment, depression, anxiety, obesity 1
- Treatment: Topiramate (first-line due to cost), onabotulinumtoxinA, or CGRP monoclonal antibodies (erenumab, fremanezumab, galcanezumab) 1
- Referral: Specialist care is usually necessary 1
New Daily Persistent Headache (NDPH)
A distinct entity where headache becomes continuous within 24 hours of onset and persists for >3 months 3:
- Characteristic feature: Patient can pinpoint exact day headache started
- Post-infectious: Can follow viral infections including SARS-CoV-2 3
- Treatment: May respond to immunomodulatory therapy (high-dose corticosteroids) if neuroinflammation suspected 3
Critical Secondary Causes (Red Flags)
Neuroimaging should be considered in the following scenarios 2:
Immediate Red Flags Requiring Urgent Evaluation
- Thunderclap headache: Subarachnoid hemorrhage 1
- Progressive worsening: Intracranial space-occupying lesion 1
- New onset in patient >50 years: Consider temporal arteritis or secondary causes 2, 1
- Headache worsened by Valsalva maneuver, coughing, sneezing, or exercise: Increased intracranial pressure 2, 1
- Awakens patient from sleep: Possible secondary headache 2
- Abnormal neurologic examination: Requires neuroimaging 2
- Neck stiffness with fever: Meningitis 1
- Focal neurological symptoms: Secondary headache 1
Specific Atypical Causes to Consider
- Acute angle-closure glaucoma: Bilateral headache with photophobia, fixed dilated pupils, elevated intraocular pressure (>21 mmHg) 4
- Chronic carbon monoxide poisoning: Episodic headaches during winter months, especially with gas heating; normal carboxyhemoglobin doesn't exclude diagnosis 5
- Sleep apnea: Morning or awakening headaches, snoring history 6
- Elevated CSF pressure in perimenopausal/menopausal women: Bilateral headache worst in morning/supine position, worsens with Trendelenburg, responds to acetazolamide or spironolactone 7
Diagnostic Approach Algorithm
- History: Document exact onset pattern, medication use (frequency and type), red flag symptoms
- Neurologic examination: If abnormal or red flags present → neuroimaging 2
- Medication review: Calculate days per month of acute medication use
- If ≥10 days/month (combination analgesics) or ≥15 days/month (simple analgesics/NSAIDs) → Diagnose MOH 1
- If MOH excluded: Assess for chronic migraine criteria (≥15 headache days/month, ≥8 migraine days/month for >3 months) 1
- If sudden onset with exact date recalled: Consider NDPH 3
- Check for comorbidities: Depression, anxiety, sleep disorders, obesity 1
Common Pitfalls to Avoid
- Don't assume normal neuroimaging excludes all secondary causes: Consider glaucoma, carbon monoxide exposure, sleep disorders 4, 5, 6
- Don't overlook MOH: It's frequently conflated with chronic migraine but requires different management 1
- Don't continue preventive medications without addressing MOH first: Withdrawal of overused medication is mandatory 1
- Don't dismiss perimenopausal women with positional headaches: Consider elevated CSF pressure syndrome 7