What red flags are
Headache red flags are clinical features that suggest a headache may be secondary to a dangerous underlying cause such as subarachnoid haemorrhage, meningitis, intracranial mass, cerebral venous sinus thrombosis, temporal arteritis (giant cell arteritis) or acute angle-closure glaucoma. Recognising these features allows patients to seek urgent evaluation rather than assuming the headache is migraine or tension-type.
The mnemonic SNOOP is commonly used: Systemic symptoms (fever, weight loss) or systemic disease (cancer, HIV); Neurological symptoms (confusion, weakness, visual loss); Onset sudden (thunderclap); Older age new-onset headache (>50 years); Pattern change (progressive, different from usual). Additional red flags include headache that is worst-ever at onset, headache worsening over days or weeks, positional headache, headache triggered by exertion, cough or Valsalva, and headache with seizures.
Related: Headache Medicine → · Dr. Jitendra Knowledge Hub → · ICHD-3 Topic →
Specific red flag symptoms requiring emergency evaluation
Thunderclap headache — sudden-onset severe headache reaching maximal intensity within seconds to minutes — is a neurological emergency requiring immediate CT brain and, if CT is negative, lumbar puncture to exclude subarachnoid haemorrhage. This is the most time-critical headache red flag. Do not wait to see if the headache improves; seek emergency care immediately.
Progressive headache worsening over days or weeks, new headache in a patient with cancer, headache with fever and neck stiffness (meningitis), headache with new neurological deficit (weakness, speech difficulty, visual loss), headache with seizures, and headache in patients over 50 with new daily headache (temporal arteritis) all require urgent neurological evaluation. Headache with papilloedema (swelling of the optic disc on fundoscopy) suggests raised intracranial pressure and needs urgent imaging.
- Thunderclap headache — worst headache of life, sudden onset — emergency
- Progressive headache worsening over days or weeks
- Fever with headache and neck stiffness — meningitis until proven otherwise
- New neurological deficit (weakness, speech difficulty, visual loss) with headache
- Headache with seizures — evaluate for mass or vascular cause
- New daily headache after age 50 — consider temporal arteritis
- Headache worse when lying flat or with cough/Valsalva
What to do if you have red flags
If you experience thunderclap headache, seek emergency care immediately — go to the nearest emergency department or call emergency services. Do not take painkillers and wait. If headache worsens progressively, is accompanied by new weakness or speech difficulty, or occurs with fever and neck stiffness, emergency evaluation is essential.
For headaches that do not meet emergency criteria but have concerning features (new pattern, new onset after 50, worsening despite treatment), prompt neurology consultation within 24–48 hours is recommended. Bring a description of the headache (onset, duration, associated symptoms, triggers), medication list, and any available medical records. Dr. Jitendra Prasad Yadav (NMC 8029) evaluates headache red flags at Kathmandu Neurology Clinic & Cognitive Center, Durbar Marg, Opposite of Yak & Yeti Hotel, with urgent assessment when indicated.