Partially treated meningitis with a lymphocytic CSF
A 55-year-old man is brought to the emergency department with two days of fever, headache, neck stiffness and vomiting. His GP prescribed oral amoxicillin 1 g three times daily 24 hours earlier. He is now drowsy but rousable, temperature 39.1 °C, pulse 110, blood pressure 132/80 mmHg, GCS 13, no focal deficit, no papilloedema and no rash. Bloods: white cells 17.8 × 10^9/L, CRP 210 mg/L, creatinine 110 micromol/L, glucose 6.8 mmol/L. Lumbar puncture after CT: opening pressure 28 cm H2O, CSF white cells 180/µL (62% neutrophils, 38% lymphocytes), protein 1.15 g/L, CSF glucose 2.3 mmol/L, Gram stain negative, CSF PCR pending.
1. How does the prior amoxicillin alter your interpretation of the CSF, and what treatment would you start now?
Read the worked answer
Prior oral amoxicillin partially treats bacterial meningitis and alters the CSF: the cell count can be lower, lymphocytes may predominate, Gram stain is frequently negative, and glucose may be less low. A neutrophil predominance is supportive but not required. The CSF here - 180 white cells, 62% neutrophils, protein 1.15 g/L, glucose 2.3 mmol/L with serum 6.8 mmol/L (ratio 0.34) - is still highly suggestive of bacterial meningitis. The negative Gram stain does not exclude it.
Empirical therapy now:
- Ceftriaxone 2 g intravenously 12-hourly (or 4 g daily). If local pneumococcal penicillin or cephalosporin resistance is significant, add vancomycin 15–20 mg/kg 8–12-hourly, targeting a trough of 15–20 mg/L.
- Add ampicillin 2 g 4-hourly if Listeria is a concern (age over 50, immunocompromise, alcohol use); he is 55, so this is reasonable until cultures are negative.
- Give dexamethasone 10 mg 6-hourly for four days, ideally before or with the first antibiotic dose. If antibiotics have already been given, the benefit is less certain, but most guidelines still recommend it when pneumococcal meningitis is likely; do not give it if there is a strong alternative diagnosis such as HSV encephalitis without bacterial suspicion.
- Start intravenous aciclovir 10 mg/kg 8-hourly until HSV PCR is negative, because drowsiness and a lymphocytic CSF can occur with HSV encephalitis.
The pitfall is to interpret the lymphocytic CSF and negative Gram stain as viral and withhold antibiotics; partially treated bacterial meningitis is the commonest mimic.
2. Was CT before lumbar puncture appropriate here, and what would you have done differently if he had a focal deficit or a GCS of 9?
Read the worked answer
CT before lumbar puncture is appropriate here because he is drowsy (GCS 13), which is a recognised indication, along with focal deficit, new-onset seizures, papilloedema and immunocompromise. The purpose is to identify a mass lesion or obstructive hydrocephalus before lumbar puncture, not to diagnose meningitis.
Crucially, antibiotics must not wait for CT. Take blood cultures, give the first antibiotic dose and dexamethasone, then send for CT and lumbar puncture. If CT shows a mass lesion or raised intracranial pressure, defer lumbar puncture and treat empirically.
If he had a focal deficit or GCS ≤8: secure the airway, give antibiotics immediately, arrange urgent CT, and involve critical care. Lumbar puncture is deferred if there is a mass or hydrocephalus. If no mass is found, lumbar puncture can proceed after imaging, but the diagnosis is often made on blood cultures and CSF when safe.
Other points: CT is not a reliable way to exclude raised intracranial pressure; a normal scan does not make lumbar puncture safe in every case. If lumbar puncture is deferred, start empirical therapy and reassess in 24–48 hours. Fundoscopy and neurological observations should be documented.
3. Blood cultures grow Streptococcus pneumoniae. Discuss the duration of therapy, the complications you would watch for, and the follow-up he needs.
Read the worked answer
Blood cultures growing Streptococcus pneumoniae confirm pneumococcal meningitis. Treat for 10–14 days intravenously; extend to 14–21 days if there are complications such as cerebritis, abscess, hydrocephalus or a persistent CSF leak. Dexamethasone is usually stopped at four days.
After the acute phase:
- Repeat imaging if he fails to improve or develops focal signs, seizures or worsening consciousness - look for subdural empyema, cerebral venous thrombosis, hydrocephalus or stroke.
- Formal audiology before discharge or at follow-up: sensorineural hearing loss is common and may be permanent.
- Look for a source: otitis media, sinusitis, mastoiditis, CSF leak, skull base fracture, or immunodeficiency (complement deficiency, hypogammaglobulinaemia, HIV, asplenia). Recurrent pneumococcal disease warrants an immunodeficiency screen.
- Notify public health. Pneumococcal meningitis does not require chemoprophylaxis for contacts; that applies to meningococcal disease.
- Vaccination: give pneumococcal conjugate and polysaccharide vaccines after recovery if not already vaccinated, plus influenza and COVID vaccination.
- Give driving and return-to-work advice, and arrange infectious diseases or neurology follow-up.
Pitfall: stopping antibiotics when the patient feels better at 5–7 days, which risks relapse, particularly with an undrained parameningeal focus.