Headache Red Flags: When the Diagnosis Changes

The vast majority of headaches presenting to clinic and emergency departments are primary — migraine, tension-type, cluster. The minority that aren't are the ones that hurt patients. The SNOOP10 framework is a structured way to find them.

SNOOP10 — what to ask, every time

Systemic symptoms (fever, weight loss) or Secondary risk factors (HIV, malignancy)
Neurological signs or symptoms (focal deficit, confusion, reduced GCS)
Onset is sudden ("thunderclap" — peak intensity in <1 minute)
Older age — new headache >50 years
Previous headache history — new pattern, different from usual
Positional — worse on lying flat (raised ICP) or sitting up (low ICP)
Precipitated by Valsalva, cough, exercise
Papilloedema on fundoscopy
Progressive headache or atypical features
Pregnancy / postpartum — wider differential including CVST
Painful eye / red eye / visual symptoms
Post-traumatic onset

Red flags and what they signal

Thunderclap headache

Subarachnoid haemorrhage until proven otherwise. Non-contrast CT head within 6 hours of onset has ≈100% sensitivity for SAH; sensitivity falls thereafter. If CT >6 hours from onset is negative, LP at 12 hours for xanthochromia.

Red flag

A "worst headache of my life" peaking in seconds is SAH until imaging and (if needed) LP say otherwise. Reversible cerebral vasoconstriction syndrome (RCVS) and cervical artery dissection are the other don't-miss diagnoses on this clinical phenotype.

Fever and headache

Bacterial meningitis if any meningism, photophobia, or altered mentation. Move fast:

Blood cultures, then IV ceftriaxone 2 g + dexamethasone 10 mg within 30 minutes
Don't delay antibiotics for CT/LP if there are no contraindications to immediate LP
CT before LP if any focal deficit, GCS <13, papilloedema, immunocompromise, or seizures

Older patient, new headache, scalp tenderness

Giant cell arteritis until proven otherwise. ESR (often >50), CRP, and a starter dose of prednisolone before the temporal artery biopsy if visual symptoms are present.

Prednisolone60 mgPO

Worse on lying flat / with Valsalva

Raised intracranial pressure. Image — and look hard at the optic discs. Causes: space-occupying lesion, idiopathic intracranial hypertension, cerebral venous sinus thrombosis (especially peri-partum or on combined oral contraceptive).

Worse on sitting up

Low-pressure headache, often post-LP or spontaneous CSF leak. Bed rest, fluids, caffeine; epidural blood patch for refractory post-LP headache.

Focal deficit

Stroke, mass lesion, encephalitis, migraine with aura (always a diagnosis of exclusion in someone without a prior history).

What you do at the bedside

For every patient with headache, even the obvious migraine:

History — onset, time-to-peak, associated features, prior pattern, drug history, recent procedures.
Examination — full neurological exam, fundoscopy, BP both arms, scalp tenderness if older, temperature.
Decision — does this fit a primary headache pattern, or has SNOOP10 been triggered? If yes — image and investigate.

Clinical pearl

A patient with known migraine can still have SAH. The question is not "do they have a primary headache disorder" but "does this headache fit their pattern?" A migraineur with a thunderclap is a thunderclap.

Key points

Apply SNOOP10 to every new or unusual headache.
Thunderclap = SAH workup until proven otherwise.
Fever + headache = meningitis workup; antibiotics within 30 minutes.
New headache >50 with scalp tenderness = GCA — start steroids before biopsy if visual.
Even a known migraineur can present with a secondary headache.

References

[1]Do TP, Remmers A, Schytz HW, et al. Red and orange flags for secondary headaches in clinical practice: SNNOOP10 list. Neurology. 2019;92(3):134-144. Link

About the author

Dr. Theo LindqvistVerifiedVerified medical practitioner

MBChB, FRCEM

Emergency Medicine· Royal London Hospital

Emergency medicine consultant with a teaching role for foundation and core trainees. Interests in resuscitation, sepsis, and time-critical decisions.