What is the diagnosis and management for a patient presenting with thunderclap headache and altered mental status?

Diagnosis and Management of Thunderclap Headache with Altered Mental Status

Subarachnoid hemorrhage (SAH) is the primary diagnosis that must be excluded immediately in any patient presenting with thunderclap headache and altered mental status, as it accounts for 10-25% of thunderclap headache cases and carries 27-44% mortality. 1

Immediate Diagnostic Approach

First-Line Imaging

• Obtain noncontrast head CT immediately on a high-quality scanner interpreted by a board-certified neuroradiologist, as this has 98.7% sensitivity for detecting SAH when performed within 6 hours of headache onset 1, 2, 3
• CT sensitivity for SAH is 98% with 99% specificity when performed acutely, making it the critical first diagnostic step 1
• The combination of thunderclap headache with altered mental status represents a medical emergency requiring urgent evaluation, as altered mental status is a common presenting symptom of life-threatening intracranial pathology 4

If CT is Negative or Non-Diagnostic

• Lumbar puncture with CSF analysis is mandatory if CT is negative or performed beyond 6 hours, as CT sensitivity drops significantly with time 1, 2, 5
• Never rely on CT alone after 6 hours from symptom onset, as failure to identify SAH leads to nearly 4-fold higher likelihood of death or disability 1
• CSF analysis should evaluate for xanthochromia, red blood cell count, and opening pressure 2, 3

Advanced Vascular Imaging

• If both CT and LP are negative, obtain brain MRI with susceptibility-weighted imaging (SWI) and vascular imaging (CTA or MRA) to evaluate for reversible cerebral vasoconstriction syndrome (RCVS), arterial dissection, cerebral venous sinus thrombosis, and other vascular pathology 1, 2
• CTA has >95% sensitivity for aneurysms ≥3mm and is faster and less invasive than conventional angiography 1

Differential Diagnosis Beyond SAH

Life-Threatening Vascular Causes

• Reversible cerebral vasoconstriction syndrome (RCVS) has become the second most common cause of thunderclap headache and is diagnosed more frequently with advances in knowledge over the past decade 2, 5, 6
• Cervical artery dissection presents with thunderclap headache in up to 20% of cases and may be associated with Horner syndrome 1, 2, 3
• Cerebral venous sinus thrombosis can present with thunderclap headache mimicking SAH, particularly when involving superior sagittal or lateral sinuses 1, 2, 3
• Intracerebral hemorrhage associated with aneurysms or vascular malformations 1, 3

Non-Vascular Life-Threatening Causes

• Intracranial infection (meningitis or encephalitis) can present with acute thunderclap headache, particularly when associated with fever and altered mental status 1, 2, 3
• In patients with recently diagnosed coccidioidal infection presenting with persistent headache and altered mental status, lumbar puncture with CSF analysis is strongly recommended, as untreated coccidioidal meningitis is nearly always fatal 4
• Spontaneous intracranial hypotension (SIH) presents with thunderclap headache followed by orthostatic headache 1, 2, 3
• Pituitary apoplexy should be considered in the differential 2, 3, 5

Clinical Assessment Priorities

Key Historical Features to Document

• Exact time to peak headache intensity (thunderclap = maximal intensity within 1 minute) 2, 3, 5
• Presence of fever, neck stiffness, seizures, or focal neurological deficits 4
• Recent head trauma, which may indicate subdural hematoma 4
• Age ≥40 years, neck pain/stiffness, witnessed loss of consciousness, onset during exertion, or limited neck flexion on examination (Ottawa SAH Rule criteria) 1

Physical Examination Essentials

• Document altered mental status severity and any focal neurological symptoms 4, 1
• Assess for neck stiffness (suggests meningitis or SAH), though Kernig's and Brudzinski's signs should not be relied upon for diagnosis 4
• Evaluate for unexplained fever (suggests meningitis) 4
• Check for signs of shock including hypotension and poor capillary refill time 4

Critical Pitfalls to Avoid

• Never assume post-SAH or recurrent headaches are benign, as rebleeding rates are 7-26% (mean 13%) in the first 2-8 weeks before aneurysm repair, and sentinel bleeds preceded major rupture in 19-20% of SAH cases 7
• Do not skip lumbar puncture based on negative CT in high-risk presentations, particularly when altered mental status is present 1
• Never delay re-imaging if clinical suspicion increases or if the patient's mental status deteriorates 7
• Maintain heightened vigilance in patients with first-degree relatives with aneurysms or autosomal dominant polycystic kidney disease (ADPKD), as these conditions are familial 1

Management Principles

• Immediate hospital admission via emergency ambulance is mandatory for all patients with suspected thunderclap headache and altered mental status, with goal arrival within one hour of assessment 4
• Treatment and prognosis depend entirely on identifying the underlying etiology through comprehensive diagnostic evaluation 3, 5
• For confirmed SAH, neurosurgical consultation is urgent to prevent rebleeding 7
• For confirmed meningitis with altered mental status, immediate empiric antibiotics and consideration of steroids per infectious disease guidelines 4