A 6-month-old infant was treated for H. influenzae meningitis. Most important investigation to be done before discharging the patient is:
**Core Concept**
H. influenzae meningitis is a serious infection that can cause severe inflammation of the meninges, leading to brain damage or death if not treated promptly. The most important investigation before discharging the patient is to evaluate the efficacy of treatment and prevent potential complications.
**Why the Correct Answer is Right**
The correct investigation to be done before discharging the patient is a lumbar puncture (LP) to check for cerebrospinal fluid (CSF) protein levels and to detect any residual or recurrent infection. The CSF protein levels can take several weeks to normalize after successful treatment of bacterial meningitis. Therefore, a follow-up LP is essential to ensure that the patient is free from infection and that the protein levels have returned to normal.
**Why Each Wrong Option is Incorrect**
**Option A:** Chest X-ray is not a relevant investigation in this scenario, as it would not provide any information about the patient's central nervous system or the effectiveness of treatment.
**Option B:** Complete Blood Count (CBC) may be useful in monitoring the patient's response to treatment, but it is not the most important investigation before discharging the patient.
**Option C:** Electroencephalogram (EEG) may be used to monitor for seizures or encephalopathy, but it is not the primary investigation to assess the effectiveness of treatment for H. influenzae meningitis.
**Clinical Pearl / High-Yield Fact**
In patients with bacterial meningitis, it is essential to perform a follow-up lumbar puncture to check for normalization of CSF protein levels, as this is a crucial indicator of successful treatment.
**Correct Answer:** C. Lumbar puncture.