What are the typical physical examination (PE) findings in a patient suspected of having encephalitis?

Physical Examination Findings in Encephalitis

The hallmark physical examination finding in encephalitis is altered mental status ranging from confusion and disorientation to stupor or coma, often accompanied by fever, focal neurological deficits, and signs of meningeal irritation. 1

Core Neurological Findings

Altered Level of Consciousness

• Disturbance of consciousness is the defining clinical feature, ranging from confusion and disorientation to obtundation or coma 1
• Patients may be unable to provide history themselves, requiring information from relatives or friends 1
• This distinguishes true encephalitis from encephalopathy, where consciousness may be less severely affected 2

Focal Neurological Deficits

• Focal neurological signs are common and reflect specific CNS tropism of different pathogens 1
• Temporal lobe involvement in HSV encephalitis may manifest as memory deficits, personality changes, or aphasia 3
• Multifocal neurological signs affecting optic nerves, brain, and spinal cord suggest ADEM rather than infectious encephalitis 1

Seizure Activity

• Focal or generalized seizures occur frequently, particularly in HSV encephalitis due to temporal lobe involvement 3, 4
• Subtle motor seizures or nonconvulsive status epilepticus may be present and require EEG for detection 5
• Temporal lobe spike-wave activity and periodic lateralized epileptiform discharges (PLEDs) are characteristic EEG findings 3, 5

Systemic Physical Examination Findings

Fever and Vital Signs

• Fever is typically present at initial presentation, though it may be absent in ADEM 1
• The combination of fever, nausea, and low ESR (<17 mm/hr) has diagnostic accuracy (AUC 0.85) for distinguishing encephalitis from other causes of encephalopathy 6

Dermatological Findings

• Rash or skin lesions may suggest specific etiologies 1
• Active vesicular lesions suggest varicella zoster virus and should be scraped for direct fluorescent antibody testing 1
• Maculopapular or petechial lesions may indicate Rocky Mountain spotted fever and warrant skin biopsy 1

Other Systemic Signs

• Upper respiratory or pulmonary findings may point to specific viral etiologies 1
• Headache is a common accompanying symptom 4
• Personality changes and behavioral abnormalities reflect limbic system involvement, particularly in HSV encephalitis 3, 6

Critical Clinical Pitfalls

What NOT to Rely On

• Normal imaging does not exclude encephalitis - approximately 10% of HSV encephalitis cases have normal initial MRI 7
• Absence of fever does not rule out encephalitis, particularly in ADEM where fever is typically absent at neurological symptom onset 1
• A single clinical finding has poor diagnostic accuracy (AUC <0.7) for distinguishing encephalitis from other causes of encephalopathy 6

When to Act Immediately

• Do not delay empiric acyclovir treatment while waiting for confirmatory testing if encephalitis is suspected clinically 3, 7, 5
• Treatment should be initiated within 6 hours of admission if viral encephalitis is suspected, as delayed treatment significantly increases mortality (8% if started within 4 days vs 28% if delayed) 3
• The standard dose is IV acyclovir 10 mg/kg every 8 hours for 14-21 days 3, 5

Diagnostic Approach Based on Physical Findings

The physical examination should trigger immediate diagnostic workup including lumbar puncture for CSF analysis (PCR for HSV, cell count, protein, glucose), MRI with diffusion-weighted imaging within 24-48 hours, and EEG if seizures are suspected 1, 3, 5

The combination of altered mental status, fever, focal neurological signs, and seizures in an encephalopathic patient should prompt immediate empiric treatment while awaiting CSF PCR results, which remain the diagnostic gold standard with >95% sensitivity and specificity 3, 8