What is the next diagnostic step for a patient with severe headache and neck pain, whose computed tomography (CT) brain scan appears normal?

Diagnostic Approach for Severe Headache with Neck Pain and Normal CT Brain

For a patient with severe "worst headache ever" for several hours associated with neck pain and a normal CT brain, a lumbar puncture (LP) is the next appropriate diagnostic step to rule out subarachnoid hemorrhage.

Rationale for Lumbar Puncture

The clinical presentation of sudden severe headache ("worst headache ever") with neck pain is highly suspicious for subarachnoid hemorrhage (SAH), which is a medical emergency requiring immediate diagnosis and management. While CT brain is the initial diagnostic test, it has limitations:

• CT sensitivity for SAH decreases over time: 98-100% within 12 hours, 93% at 24 hours, and only 57-85% by day 6 1
• CT can be normal in up to 2-5% of patients with SAH even when performed within 12 hours of symptom onset 2
• The combination of severe headache and neck pain significantly increases the pretest probability of SAH

Evidence Supporting Lumbar Puncture

The Canadian Stroke Best Practice Guidelines specifically recommend:

• "In patients with a new acute headache suspicious of SAH, a third-generation or higher CT scan performed within six-hours of onset of headache and read as normal by a neuroradiologist; a lumbar puncture is not required [Evidence Level B]." 3
• "If there is a high clinical index of suspicion of SAH and no availability of an experienced neuroradiologist to review the CT imaging, then a lumbar puncture and cerebral spinal fluid (CSF) analysis should be performed [Evidence Level C]." 3
• "If a lower generation CT scan is done and read as normal, and the clinical suspicion of SAH is high, or if the CT is performed after six-hours, or is not read by an experienced radiologist or the patient is in an altered state of consciousness, a lumbar puncture should be performed." 3

Diagnostic Algorithm

1. Initial presentation: Severe "worst headache ever" with neck pain

   • This presentation is classic for SAH and requires urgent evaluation

2. CT brain (already performed): Normal

   • A normal CT does not exclude SAH with 100% certainty

3. Next step: Lumbar puncture (LP)

   • Looking for xanthochromia (yellow discoloration of CSF) which occurs due to hemoglobin breakdown into bilirubin following SAH 1
   • Xanthochromia evaluation is most sensitive after 12 hours from headache onset 1

4. If LP positive: Proceed with vascular imaging

   • "Patients with SAH should undergo vascular imaging of the brain to investigate the cause of the hemorrhage. High-quality CTA may be initially preferable to catheter angiography [Evidence Level B]" 3

5. If LP negative: Consider alternative diagnoses or additional imaging based on clinical suspicion

Important Considerations

• Timing matters: Xanthochromia is most sensitive after 12 hours from headache onset 1, so timing the LP appropriately is crucial
• Interpretation: Xanthochromia with a low red blood cell count strongly suggests SAH, while xanthochromia with a high red blood cell count may be due to traumatic tap 1
• Contraindications: LP should not be performed if there are signs of elevated intracranial pressure with evidence of a mass lesion 4

Why Not Other Options?

• MRI brain (option A): While MRI can detect SAH using FLAIR sequences and identify other causes of headache not visible on CT 1, it is not the standard next step after a normal CT in suspected SAH according to guidelines
• MRI (option C): Similar to option A, not the recommended next step per guidelines
• Discharge with paracetamol (option D): Inappropriate and potentially dangerous given the high suspicion for SAH, which has a mortality rate of over 40% within 30 days if untreated 3

The evidence clearly supports performing a lumbar puncture as the next diagnostic step for this patient with severe headache, neck pain, and a normal CT brain to definitively rule out subarachnoid hemorrhage.