Acute Infections of the Central Nervous System: Focus on Bacterial Meningitis and Herpes Simplex Encephalitis

Abstract

Acute infectious diseases of the central nervous system, particularly bacterial meningitis and herpes simplex encephalitis (HSE), are neurological emergencies. These diseases often have no definitive symptoms or signs, which makes diagnosis difficult. Delayed diagnosis or treatment of bacterial meningitis or HSE leads to a poor prognosis.

If bacterial meningitis is clinically diagnosed, optimal antimicrobial therapy should be started within 1 h after initial contact with the patient. In Japan, pneumococcal and Haemophilus influenzae type b (Hib) meningitis account for 75% of all community-acquired bacterial meningitis cases, and most causative pathogens of these meningitis are resistant to ampicillin and third-generation cephem antibiotics. If pneumococcal meningitis is suspected, the choice of antibiotics should be strategically determined on the assumption that the etiologic agent is penicillin-resistant Streptococcus pneumoniae in Japan. Hib and pneumococcal vaccines contribute to reducing the frequency of bacterial meningitis.

The etiology of acute encephalitis is often unknown. HSE is one of the major causes, and its prognosis is extremely poor without treatment. Acyclovir (ACV) is the most efficient agent for the treatment of HSE. If acute encephalitis is clinically diagnosed, treatment with intravenous ACV (10 mg/kg, every 8 h for 14–21 days in immunocompetent patients) should be immediately started. In definitive HSE patients, ACV treatment should not be stopped until confirmation of HSV-negative polymerase chain reaction results in cerebral spinal fluid samples on two separate occasions. In patients with ACV-resistant HSE, adjunctive vidarabine or foscarnet should be considered.