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Aseptic Meningitis

Summary

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  • Inflammation of the meninges without bacterial infection
  • Typically caused by viruses, but can also be due to drugs, autoimmune conditions, or malignancies
  • Characterised by fever, headache, and neck stiffness with negative bacterial cultures

Pathophysiology

  • Viral invasion of the central nervous system (CNS)
    • Direct infection of meningeal and ependymal cells
    • Immune-mediated inflammation
  • Non-viral causes:
    • Drug-induced hypersensitivity reactions
    • Autoimmune processes (e.g., systemic lupus erythematosus)
    • Paraneoplastic syndromes

Demographics

  • Can affect all age groups
  • More common in children and young adults
  • Seasonal variation:
    • Enteroviruses peak in summer and early fall
    • Arboviruses more prevalent in warmer months

Diagnosis

  • Clinical presentation:
    • Fever, headache, neck stiffness
    • Photophobia, nausea, vomiting
  • Cerebrospinal fluid (CSF) analysis:
    • Pleocytosis (>5 white blood cells/μL)
    • Normal or mildly elevated protein
    • Normal glucose
    • Negative bacterial cultures
  • Polymerase chain reaction (PCR) for viral pathogens
  • Serology for specific viral antibodies

Imaging

  • Neuroimaging not routinely required for uncomplicated cases
  • MRI findings (when performed):
    • Normal in most cases
    • Possible leptomeningeal enhancement
    • Exclude complications or alternative diagnoses
  • CT scan:
    • Limited role in diagnosis
    • May be used to rule out increased intracranial pressure before lumbar puncture

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  • A 70-year-old patient presented with dysarthria and and right sided upper limb numbness.
  • FLAIR and diffusion-weighted sulcal hyperintensity and leptomeningeal enhancement regressed after two months of a tapering steroid regimen.
  • Biopsy revealed a chronic lymphocystic meningitis that was assumed to be related to the patient's longstanding rheumatoid arthritis.

Treatment

  • Supportive care:
    • Hydration
    • Analgesics for pain and fever
    • Anti-emetics for nausea
  • Antiviral therapy:
    • Acyclovir for suspected herpes simplex virus (HSV) meningitis
    • Ganciclovir for cytomegalovirus (CMV) meningitis
  • Discontinuation of offending drugs in drug-induced cases
  • Immunomodulatory therapy for autoimmune causes
  • Monitoring for potential complications:
    • Increased intracranial pressure
    • Seizures
    • Cognitive impairment

Differential diagnosis

Differential Diagnosis Distinguishing Feature
Bacterial Meningitis Diffuse intense leptomeningeal enhancement; may show cerebritis, subdural empyema, or hydrocephalus on MRI
Viral Encephalitis Temporal lobe and limbic T2/FLAIR signal abnormality on MRI; cortical restricted diffusion in active disease
Tuberculous Meningitis Basilar predominant meningeal enhancement; perforator territory infarcts; communicating hydrocephalus
Subarachnoid Haemorrhage Hyperdense cisternal blood on CT; sulcal FLAIR signal without enhancement pattern
Brain Abscess Ring-enhancing lesion with restricted DWI centrally; smooth thin capsule; surrounding vasogenic oedema
Neoplastic Meningitis Nodular leptomeningeal enhancement along cranial nerves, spinal roots and pia; may show communicating hydrocephalus
Autoimmune Meningitis Smooth or nodular pachymeningeal or leptomeningeal enhancement; hypothalamic or infundibular involvement in some subtypes