Headache — Written Clinical Reasoning

SAQ 1 — Headache with Red Flags: Differential, Investigation, and Management (20 marks, 30 minutes)

Prompt: Outline your systematic approach to this patient, including: (a) the SNNOOP10 red-flag screen and which red flags she has (4 marks); (b) your differential diagnosis and the single most likely diagnosis (4 marks); (c) the immediate investigations and their interpretation (5 marks); (d) the immediate management with exact drugs, doses, and rationale (4 marks); and (e) how this presentation differs from her usual migraine and why the difference matters (3 marks). ^[1]

Case vignette: A 58-year-old woman with known unilateral migraine on propranolol presents with 3 days of progressive bifrontal headache unlike her usual migraine, fever 38.2, neck stiffness, CRP 89 with neutrophilic leucocytosis. CT head normal, fundoscopy normal, no focal deficit, GCS 15. ^[1]

Model Answer

(a) SNNOOP10 red-flag screen (4 marks): ^[1]

This patient has multiple red flags on the SNNOOP10 screen ^[1]. The relevant items are:

• S — Systemic symptoms: She has fever (38.2 degrees), raised inflammatory markers (CRP 89, neutrophilic leucocytosis). This screens for infection, malignancy, and autoimmune disease — all of which are on the differential.
• N — Neurologic deficit: She does not have a focal neurological deficit on examination, but the headache pattern has changed (see below).
• O — Onset: The headache is not thunderclap (it developed over 3 days), so subarachnoid haemorrhage is less likely but not excluded.
• P — Pattern change: This headache is different from her usual migraine — it is bifrontal rather than unilateral, progressive over days, associated with fever, and not relieved by her usual measures. Pattern change is a critical red flag requiring investigation.
• (Positional and Precipitated by Valsalva): Not reported in this vignette.
• (Papilloedema): Absent — fundoscopy is normal.

The presence of fever plus neck stiffness plus a changed headache pattern triggers investigation for a secondary cause. A primary headache diagnosis should not be accepted in a patient with systemic signs of infection. ^[1]

(b) Differential diagnosis and most likely diagnosis (4 marks): ^[1]

The differential for headache with fever and neck stiffness includes:

1. Bacterial meningitis (most urgent) — S. pneumoniae, N. meningitidis, and (given her age over 50) Listeria monocytogenes
2. Viral meningitis (enterovirus, HSV-2, VZV) — less likely given the marked neutrophilic leucocytosis and high CRP, but possible
3. Encephalitis (HSV) — less likely as her GCS is 15 and there are no seizures or focal deficits, but must be considered
4. Subarachnoid haemorrhage — less likely given the subacute onset over 3 days (SAH is typically thunderclap), but meningism can follow a small sentinel leak
5. Cerebral abscess or parameningeal infection — particularly if there is a source (sinusitis, otitis media, dental infection)
6. GCA-related headache with systemic inflammation — possible given her age (58), but GCA does not typically cause fever of 38.2 degrees and neck stiffness ^[1]

The single most likely diagnosis is acute community-acquired bacterial meningitis, given the fever, neck stiffness, raised inflammatory markers, and the neutrophilic leucocytosis. The changed headache pattern from her baseline migraine is the key — this is not her usual headache. ^[1]

(c) Immediate investigations and their interpretation (5 marks): ^[1]

1. Blood cultures (two sets) before antibiotics — if possible without delaying therapy
2. Lumbar puncture — if there are no contraindications on CT (and there are none — no mass, no shift). The CT is already normal, so LP can proceed. CSF should be sent for:
   • Cell count and differential, glucose (with a simultaneous serum glucose), protein, Gram stain, culture
   • Meningitis/encephalitis multiplex PCR panel (detects S. pneumoniae, N. meningitidis, H. influenzae, L. monocytogenes, C. neoformans, HSV-1/2, VZV, enterovirus)
   • Opening pressure should be measured
3. Additional blood tests — coagulation profile, urea and electrolytes (for baseline before antibiotics and for SIADH monitoring), liver function, lactate
4. HIV test — relevant if the CSF pattern is atypical or if opportunistic infection is suspected
5. Consider temporal artery ultrasound — if CSF is negative and GCA remains in the differential, though the presentation favours infection ^[1]

The expected CSF pattern in bacterial meningitis is: elevated opening pressure, neutrophilic pleocytosis (typically hundreds to thousands of cells), low glucose (below 40 per cent of serum), high protein (above 1 g/L), and Gram stain positive for organisms. A lymphocytic pattern with normal glucose would suggest viral meningitis. ^[1]

(d) Immediate management with exact drugs, doses, and rationale (4 marks): ^[1]

The priority is to start empiric antibiotics immediately, without waiting for the LP result. The empiric regimen for suspected community-acquired bacterial meningitis in this patient (over 50, so at risk for Listeria) is: ^[1]

• Ceftriaxone 2 g IV every 12 hours — covers S. pneumoniae and N. meningitidis
• Vancomycin (loading dose 25-30 mg/kg, then adjusted to trough levels) — covers penicillin-resistant pneumococcus
• Ampicillin 2 g IV every 4 hours — covers Listeria monocytogenes (intrinsically resistant to cephalosporins; critical in patients over 50, immunocompromised, pregnant, or alcoholic)
• Dexamethasone 10 mg IV every 6 hours — given before or with the first antibiotic dose if pneumococcal meningitis is suspected; suppresses the inflammatory cascade from bacterial lysis ^[1]

If there is any clinical suggestion of encephalitis (altered mental status, seizures, focal neurology), add aciclovir 10 mg/kg IV every 8 hours until HSV PCR is negative. ^[1]

The rationale: antibiotics must not be delayed for LP or CT. The LP confirms the diagnosis and guides targeted therapy, but empiric therapy starts on suspicion. The ampicillin is essential because her age over 50 places her at risk for Listeria, which is not covered by ceftriaxone alone. ^[1]

(e) How this presentation differs from her usual migraine and why it matters (3 marks): ^[1]

Her usual migraine is unilateral, throbbing, lasts hours, occurs 2-3 days per month, and is controlled on propranolol. This presentation is different in every dimension: it is bifrontal (not unilateral), progressive over days (not hours), associated with fever and neck stiffness (not nausea and photophobia alone), and not relieved by her usual measures. This pattern change is a critical red flag (the P — Pattern change in SNNOOP10) and is the reason this patient requires investigation rather than assuming it is an atypical migraine. The principle: a headache that is different from a patient's established pattern, especially with systemic features, demands a search for a secondary cause. ^[1]