What are the differential diagnoses for a patient presenting to the Emergency Department (ED) with fever, altered level of consciousness, and electrocardiogram (ECG) changes including borderline sinus bradycardia with cerebral T waves?

Differential Diagnoses for Fever, Altered Consciousness, and Cerebral T Waves

The primary differential diagnoses are bacterial meningitis, viral encephalitis, and subarachnoid hemorrhage, with the ECG findings of cerebral T waves strongly suggesting an intracranial catastrophe, particularly subarachnoid hemorrhage or severe encephalitis. 1

Key Clinical Context

The combination of fever and altered consciousness mandates urgent consideration of central nervous system infection or hemorrhage. Cerebral T waves (deep, symmetrical T-wave inversions) on ECG are pathognomonic for intracranial pathology, particularly subarachnoid hemorrhage, but can also occur with severe encephalitis or any condition causing elevated intracranial pressure. 1 The borderline bradycardia (60 bpm) may represent early Cushing's triad if intracranial pressure is rising.

Primary Differential Diagnoses

1. Bacterial Meningitis

• The classic triad of fever, neck stiffness, and altered consciousness is present in less than 50% of cases, making this diagnosis challenging but critical not to miss 1
• Fever, altered mental status, and headache are the most common presenting features 1
• Urgent hospital referral is mandatory due to possibility of rapid deterioration 1
• Elderly patients are more likely to have altered consciousness and less likely to have neck stiffness or fever 1
• Pneumococcal meningitis is more likely to cause seizures, focal neurological symptoms, and reduced consciousness 1

2. Viral or Infectious Encephalitis

• Encephalitis shares many clinical features with meningitis, including fever, headache, and altered consciousness 1
• Mental status changes early in disease course are generally more common in encephalitis than meningitis 1
• Additional features include acute cognitive dysfunction, behavioral changes, focal neurologic signs, and seizures 1
• Documented fever ≥38°C within 72 hours before or after presentation is a minor criterion for encephalitis diagnosis 1
• The cerebral T waves on ECG suggest significant brain parenchymal involvement 2

3. Subarachnoid Hemorrhage (SAH)

• Cerebral T waves are highly characteristic of SAH and other intracranial catastrophes 1
• May present with fever (chemical meningitis from blood in subarachnoid space) and altered consciousness
• The ECG changes reflect autonomic dysregulation from hypothalamic/brainstem involvement
• Bradycardia may indicate rising intracranial pressure (Cushing's triad component)

4. Meningococcal Sepsis with Meningitis

• Can present with hypotension, altered mental state, and rash (typically purpuric or petechial) 1
• Patients can deteriorate rapidly, and shock ensues; must be monitored frequently even if initially appearing well 1
• Meningitis occurs in about 60% of meningococcal disease cases 1
• 10-20% may have fulminant sepsis with or without meningitis 1

5. Bickerstaff Brainstem Encephalitis (BBE)

• The core diagnostic triad consists of altered mental status, external ophthalmoplegia, and ataxia 3
• Part of the Guillain-Barré syndrome spectrum 4
• Altered consciousness is a distinguishing feature occurring alongside ophthalmoplegia and ataxia 4
• Areflexia is a hallmark feature occurring at some point during clinical course 4
• Can be misdiagnosed as other forms of encephalitis or brainstem lesions 4

Critical "Red Flags" to Assess

The following warning signs must be rapidly recognized: 5

• Pupillomotor disturbances
• Focal neurologic deficits
• Meningismus (neck stiffness)
• Headache
• Tachycardia and tachypnea (with or without fever)
• Muscle contractions or myoclonus
• Skin abnormalities (petechial or purpuric rash)

Immediate Diagnostic Approach

Essential Initial Workup

• Neuroimaging (CT head without contrast) is mandatory before lumbar puncture if focal deficits, altered consciousness, or concern for elevated intracranial pressure 1
• Lumbar puncture for CSF analysis (collect at least 20cc) including cell count, protein, glucose, Gram stain, culture, and PCR studies 3
• Blood cultures before antibiotics 1
• Complete metabolic panel to exclude metabolic encephalopathy 5
• EEG should be considered for nonconvulsive status epilepticus, which can present as altered consciousness 1

Neuroimaging Considerations

• MRI brain with and without contrast should be performed within 48 hours if encephalitis suspected, looking for T2/FLAIR hyperintensities in brainstem, cerebellum, basal ganglia, thalamus, or spinal cord 3
• CT angiography if SAH suspected based on cerebral T waves
• The yield of neuroimaging in atraumatic altered mental status is approximately 11% for relevant abnormal findings 1

Common Pitfalls to Avoid

1. Do not wait for the "classic triad" of meningitis symptoms—it is present in less than 50% of cases 1
2. A completely normal ECG does not exclude acute coronary syndrome, but cerebral T waves strongly suggest intracranial pathology, not cardiac ischemia 1
3. Kernig's and Brudzinski's signs have high specificity (up to 95%) but sensitivity as low as 5%—their absence does not exclude meningitis 1
4. Elderly patients may not mount a fever despite serious CNS infection 1
5. Do not delay antibiotics for neuroimaging or lumbar puncture if bacterial meningitis is suspected—give empiric antibiotics immediately 1
6. Nonconvulsive status epilepticus can present as altered consciousness without motor seizures—maintain high index of suspicion 1

Immediate Management Priorities

While diagnostic workup proceeds, empiric treatment should be initiated immediately if bacterial meningitis or HSV encephalitis cannot be excluded: 1

• Empiric antibiotics (ceftriaxone + vancomycin, add ampicillin if >50 years or immunocompromised for Listeria coverage)
• Acyclovir for presumed HSV encephalitis
• Dexamethasone if bacterial meningitis suspected (before or with first antibiotic dose)
• Supportive care with airway protection if Glasgow Coma Scale <8