Central Nervous System Infections

The answer first

CNS infection is the specialty where sequence saves lives. Three rules cover almost every scenario you will meet, in exams and on call ^[1]:

1. Antibiotics before imaging, every time. If bacterial meningitis is plausible, take blood cultures and give ceftriaxone (plus vancomycin per local protocol, plus ampicillin if the patient is over 50 or immunosuppressed) immediately. The CT and the LP come after. Every hour of delay worsens outcome ^{[1] [3]}.
2. Confusion means encephalitis — start aciclovir. Fever with headache alone is meningitis until proven otherwise; fever with altered behaviour, personality change, seizures or dysphasia is encephalitis until proven otherwise, and the treatable cause is HSV. Aciclovir 10 mg/kg TDS IV starts on suspicion, not on PCR confirmation ^[5].
3. The LP is diagnostic, not optional — but respect the two gates. Gate one: CT first if immunosuppression, seizures, papilloedema, focal signs or reduced consciousness (Hasbun criteria). Gate two: measure the opening pressure, because in cryptococcal meningitis the pressure itself kills and serial drainage is treatment ^{[4] [7]}.

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References10ShowHide

1. [1]van de Beek D, de Gans J, Tunkel AR, Wijdicks EF. Community-acquired bacterial meningitis in adults N Engl J Med, 2006.PMID 16394301
2. [2]de Gans J, van de Beek D; European Dexamethasone in Adulthood Bacterial Meningitis Study Investigators. Dexamethasone in adults with bacterial meningitis N Engl J Med, 2002.PMID 12432041
3. [3]Tunkel AR, Hartman BJ, Kaplan SL, et al. Practice guidelines for the management of bacterial meningitis Clin Infect Dis, 2004.PMID 15494903
4. [4]Hasbun R, Abrahams J, Jekel J, Quagliarello VJ. Computed tomography of the head before lumbar puncture in adults with suspected meningitis N Engl J Med, 2001.PMID 11742046
5. [5]Whitley RJ, Alford CA, Hirsch MS, et al. Vidarabine versus acyclovir therapy in herpes simplex encephalitis N Engl J Med, 1986.PMID 3001520
6. [6]Dalmau J, Lancaster E, Martinez-Hernandez E, Rosenfeld MR, Balice-Gordon R. Clinical experience and laboratory investigations in patients with anti-NMDAR encephalitis Lancet Neurol, 2011.PMID 21163445
7. [7]Day JN, Chau TT, Wolbers M, et al. Combination antifungal therapy for cryptococcal meningitis N Engl J Med, 2013.PMID 23550668
8. [8]Jarvis JN, Lawrence DS, Meya DB, et al. Single-Dose Liposomal Amphotericin B Treatment for Cryptococcal Meningitis N Engl J Med, 2022.PMID 35320642
9. [9]Brouwer MC, Tunkel AR, McKhann GM 2nd, van de Beek D. Brain abscess N Engl J Med, 2014.PMID 25075836
10. [10]Thwaites GE, Nguyen DB, Nguyen HD, et al. Dexamethasone for the treatment of tuberculous meningitis in adolescents and adults N Engl J Med, 2004.PMID 15496623