What are the red flags in headache diagnosis?

Red Flags in Headache Diagnosis

When evaluating headaches, specific red flag features demand immediate investigation to rule out life-threatening secondary causes, with thunderclap headache, new neurological deficits, and onset after age 50 being the most critical warning signs requiring urgent neuroimaging and possible lumbar puncture. 1, 2

Critical Historical Red Flags

Immediate Life-Threatening Features

• Thunderclap headache (sudden onset reaching maximum intensity within seconds to minutes) strongly suggests subarachnoid hemorrhage and requires emergent evaluation 1, 2
• "Worst headache of life" with abrupt onset indicates serious vascular pathology 1, 2
• New headache onset after age 50 raises concern for temporal arteritis or other secondary causes 1, 2

Progressive or Changing Patterns

• Marked change in previously stable headache pattern signals potential secondary headache 1, 2
• Progressive headache worsening over time suggests intracranial space-occupying lesion 1, 2
• Headache awakening patient from sleep may indicate increased intracranial pressure 1, 2

Positional and Exertional Features

• Headache aggravated by coughing, sneezing, or exercise suggests intracranial hypertension or space-occupying lesion 1, 2
• Positional headache may indicate intracranial hypertension or hypotension 2

Associated Systemic Features

• Headache with weight loss and/or memory/personality changes indicates secondary headache, possibly malignancy 1, 2
• Persistent headache following head trauma may indicate intracranial injury or subdural hematoma 1, 2
• Atypical aura can represent transient ischemic attack, stroke, epilepsy, or arteriovenous malformations 1, 2

Physical Examination Red Flags

Neurological Findings

• Focal neurological symptoms or signs strongly suggest secondary headache and warrant immediate imaging 1, 2
• Altered consciousness or personality changes indicate serious intracranial pathology 1, 2
• Uncoordination may indicate cerebellar pathology 1, 2

Meningeal Signs

• Neck stiffness suggests meningitis or subarachnoid hemorrhage 1, 2
• Limited neck flexion on examination is part of the Ottawa SAH Rule 1
• Unexplained fever raises concern for meningitis 1, 2

Ottawa SAH Rule for Risk Stratification

For alert patients >15 years with new severe nontraumatic headache reaching maximum intensity within 1 hour, investigate for subarachnoid hemorrhage if ANY of the following are present: 1

1. Age ≥40 years
2. Neck pain or stiffness
3. Witnessed loss of consciousness
4. Onset during exertion
5. Thunderclap headache (instantly peaking pain)
6. Limited neck flexion on examination

Diagnostic Approach Based on Red Flags

Imaging Strategy

• When red flags are present, neuroimaging is mandatory to rule out secondary causes 1, 2
• MRI is preferred over CT due to higher resolution and absence of radiation exposure, except when acute intracranial hemorrhage is suspected 1, 2
• For suspected acute hemorrhage, use noncontrast CT as the initial imaging modality 1

Timing-Based Protocol for Thunderclap Headache

• Patients presenting <6 hours from onset without neurological deficit: Noncontrast head CT on high-quality scanner interpreted by board-certified neuroradiologist is reasonable 1
• Patients presenting >6 hours from onset OR with new neurological deficit: Perform noncontrast head CT followed by lumbar puncture if CT is negative for subarachnoid hemorrhage 1

Evidence Quality and Clinical Performance

Recent multinational ED data shows that new neurological deficit, history of neoplasm, older age (>50 years), and recent head trauma (2-7 days prior) were independent predictors of serious secondary headache 3. The combined sensitivity of red flag criteria was 96.5% but specificity was only 5.1%, with positive predictive value of 9.3% 3. This means red flags are excellent for ruling out serious causes when absent (negative predictive value 93.5%) but result in many false positives 3.

Critical Pitfalls to Avoid

• Never rely solely on neuroimaging without considering the complete clinical picture 1
• Do not overlook the need for neuroimaging when red flags are present 2
• Serious underlying disease rarely mimics typical migraine or tension headache exactly—atypical features should prompt investigation 4
• Some serious causes may be "CT-negative" (arterial dissection, encephalitis, vasculitides, cerebral venous thrombosis) and require MRI and/or lumbar puncture 4