What are the differences between meningitis and encephalitis in terms of presentation, diagnosis, and treatment?

Meningitis vs. Encephalitis: Key Differences

Meningitis is inflammation of the meninges (membranes covering the brain) presenting primarily with headache and neck stiffness, while encephalitis is inflammation of the brain parenchyma itself, distinguished by altered mental status, focal neurological deficits, and seizures. 1, 2

Anatomic and Pathophysiologic Distinctions

Site of Inflammation:

• Meningitis affects the leptomeninges (connective tissue membranes covering the brain), not the brain tissue itself 3
• Encephalitis involves direct inflammation of the brain parenchyma, resulting from direct infection, post-infectious processes like ADEM, or autoimmune conditions 1

The single distinguishing clinical element between these diagnoses is the presence of altered consciousness, focal deficits, and seizures in encephalitis 4

Clinical Presentation Differences

Meningitis Presentation:

• Fever, headache, and nuchal rigidity (neck stiffness) form the classic triad 2, 3
• Vomiting and photophobia are common 3
• Mental status is typically preserved unless severe or complicated 2
• Neurological deficits are generally absent 2

Encephalitis Presentation:

• Altered mental status is a required major criterion - manifesting as confusion, disorientation, behavioral changes, or other cognitive impairments lasting ≥24 hours 1
• Seizures occur in approximately one-third of patients, which may be generalized or focal 1, 5
• Focal neurological deficits are common 2, 4
• Psychiatric manifestations including behavioral changes and personality changes occur in 41-76% of cases 5
• Speech disturbances occur in 59% of patients 5
• Fever may be present but can be low-grade or absent, particularly in immunosuppressed patients 1, 5

Important caveat: When both meningeal and parenchymal inflammation coexist, the term "meningoencephalitis" is used 4

Diagnostic Approach Differences

CSF Analysis:

• Both conditions show CSF pleocytosis (≥5 WBC/mm³), though this is more consistently present in meningitis 1
• Critical distinction: Encephalitis can occur without significant CSF pleocytosis, particularly in immunocompromised patients or early in the course 1
• In meningitis, CSF inflammation is typically more pronounced with higher cell counts 1

Neuroimaging:

• Meningitis: CT or MRI may show meningeal enhancement but brain parenchyma is typically normal 3
• Encephalitis: MRI (preferred over CT) shows parenchymal abnormalities in approximately 90% of cases, though normal imaging does not exclude the diagnosis 1, 6
• MRI detects early cerebral changes in 90% of encephalitis cases versus only 25% sensitivity for CT 7, 6

EEG:

• Meningitis: Generally not indicated unless complications develop 2
• Encephalitis: Abnormal in >80% of cases; obtain when distinguishing psychiatric versus organic causes or when subtle seizures are suspected 7, 6
• EEG patterns may be suggestive of specific etiologies (e.g., temporal lobe sharp waves in HSV-1) 1

Treatment Differences

Meningitis Management:

• Primarily antimicrobial therapy directed at bacterial or viral pathogens 1, 2
• CSF testing for enteroviruses, HSV-1, HSV-2, and VZV by PCR 1
• Viral meningitis is often self-limiting but can cause significant morbidity 1
• Follow-up hearing tests required within 4 weeks if hearing may be affected 1

Encephalitis Management:

• Requires immediate neurological specialist assessment within 24 hours 7, 6
• High-dose corticosteroids are first-line for ADEM and autoimmune encephalitis 5, 7, 6
• Patients with declining consciousness require urgent ICU assessment for airway protection, ventilatory support, and intracranial pressure management 7, 6
• Seizure management with IV valproate (88% efficacy) or levetiracetam (73% efficacy); avoid phenytoin as first-line (only 56% efficacy) 7
• Etiology-specific treatments: HSV requires acyclovir, cerebral malaria requires quinine/artemether, toxoplasmosis requires pyrimethamine plus sulfadiazine 7, 6

Prognostic and Outcome Differences

Meningitis:

• Viral meningitis is rarely fatal in immunocompetent adults but causes significant morbidity 1
• Sequelae include hearing loss (requiring cochlear implant assessment if severe), headaches in up to one-third, and fatigue 1
• Bacterial meningitis has higher mortality and requires post-discharge follow-up for all confirmed cases 1

Encephalitis:

• Higher morbidity and mortality than meningitis 2, 8
• 30-50% develop long-term neurological or psychiatric sequelae including cognitive deficits, epilepsy, movement disorders, anxiety, depression, and obsessive behaviors 7
• All patients require comprehensive rehabilitation assessment, as sequelae may not be immediately apparent at discharge 5, 7, 6
• Behavioral changes can be mistaken for primary psychiatric illness, leading to diagnostic delays 5

Critical Management Pitfalls

Common diagnostic error: Distinguishing encephalitis from encephalopathy (altered mental status without brain inflammation) is challenging, as both present with confusion but only encephalitis requires inflammation markers 1

Do not discharge patients with suspected encephalitis without either a definite or suspected diagnosis and comprehensive rehabilitation planning 5, 6

In resource-limited settings where MRI is unavailable, diagnosis must rely on clinical criteria and CSF analysis, accepting lower diagnostic certainty 1