Differential Diagnoses for Headache
Primary Headache Disorders
Migraine without aura is characterized by recurrent moderate-to-severe unilateral, pulsating headache lasting 4-72 hours with nausea/vomiting, photophobia, and phonophobia that worsens with routine activity 1. Diagnosis requires at least 5 lifetime attacks meeting these criteria 1.
Migraine with aura presents with the above features plus recurrent short-lasting visual or hemisensory disturbances that precede or accompany the headache 1. The aura typically spreads gradually over ≥5 minutes and lasts less than 60 minutes 1.
Chronic migraine occurs on ≥15 headache days per month for more than 3 months, with ≥8 days meeting migraine criteria 1. This represents a distinct entity with substantially greater burden than episodic migraine 1.
Tension-type headache is the most prevalent primary headache disorder affecting 38% of the population 2. It presents as bilateral, mild-to-moderate pressing or tightening quality pain that is not aggravated by routine physical activity and lacks the accompanying symptoms of migraine 3, 1.
Cluster headache affects approximately 0.1% of the population and features strictly unilateral severe headache lasting 15-180 minutes with ipsilateral autonomic symptoms including lacrimation, conjunctival injection, nasal congestion, ptosis, or miosis 3, 1.
Secondary Headache Disorders
Subarachnoid hemorrhage presents as thunderclap headache described as the "worst headache of life" and may include altered taste sensation 1. Non-contrast CT has 95% sensitivity on day 0, declining to 74% on day 3 and 50% at 1 week 1, 4.
Meningitis manifests with headache accompanied by neck stiffness and unexplained fever 1. This represents a life-threatening condition requiring immediate evaluation 3.
Brain tumor or space-occupying lesion typically causes progressive headache that awakens the patient from sleep and worsens with Valsalva maneuver or coughing 1. However, the yield of neuroimaging in patients with headache and normal neurologic examination reveals brain tumors in only 0.8% of cases 4.
Giant cell arteritis should be suspected in patients over 50 years with new-onset headache, scalp tenderness, and jaw claudication 1. ESR and CRP should be checked, though ESR can be normal in 10-36% of giant cell arteritis cases 1, 4.
Stroke or TIA may present with atypical aura featuring focal neurological symptoms 1.
Medication-overuse headache develops with ≥15 headache days per month and regular overuse of acute medications (non-opioid analgesics ≥15 days/month or other acute medications ≥10 days/month) for more than 3 months 1. This commonly develops from overuse of acute medication to treat migraine attacks 3.
Spontaneous intracranial hypotension presents as orthostatic headache that is absent or mild on waking, begins within 2 hours of upright posture, and improves more than 50% within 2 hours of lying flat 1.
Increased intracranial pressure causes headache worsening with coughing, sneezing, or exercise 1.
Critical Red Flags Requiring Urgent Investigation
Thunderclap headache with abrupt onset always warrants immediate evaluation for subarachnoid hemorrhage 1, 5.
New-onset headache after age 50 increases the likelihood of serious pathology including stroke, temporal arteritis, neoplasm, and subdural hematoma, with up to 15% of patients over 65 years having serious pathology 1, 4.
Progressive worsening headache over weeks to months suggests space-occupying lesion or other structural pathology 1.
Atypical aura with focal neurological symptoms or duration exceeding 60 minutes may indicate stroke or other serious pathology 3, 1.
Recent head or neck trauma necessitates evaluation for subdural or epidural hematoma, which occurs in 1-3% of mild head injury patients 5, 4.
Headache awakening patient from sleep or brought on by Valsalva, cough, or exertion suggests increased intracranial pressure or structural lesion 1, 5.
Focal neurological symptoms or signs on examination significantly increase the probability of detecting clinically significant intracranial pathology 1, 5.
Unexplained fever with neck stiffness indicates possible meningitis or other infectious process 1.
Altered consciousness, memory, or personality suggests serious intracranial pathology requiring immediate investigation 1.