**Question:** A baby boy is brought to the hospital because of convulsion. In the course of work up, his body temperature & plasma glucose are normal but his CSF glucose is 12 mg/ dl. A possible explanation is

A. Hypoglycemia
B. Hyperglycemia
C. Infection
D. Brain Tumour

**Core Concept:**
The presented scenario involves a baby boy with seizures, normal plasma glucose, and low cerebrospinal fluid (CSF) glucose levels. The differential diagnoses revolve around hypoglycemia, hyperglycemia, infection, and brain tumor. A low CSF glucose level is indicative of increased brain cell activity, such as in seizures, inflammation, or neoplasm. Normal plasma glucose levels eliminate hypoglycemia as a cause.

**Why the Correct Answer is Right:**
The correct answer is **D.** Brain Tumour because low CSF glucose levels are most commonly associated with increased brain cell activity due to conditions like brain tumors, infections, or inflammation. In this case, the low CSF glucose level suggests an underlying pathology involving the brain. The normal plasma glucose level eliminates hypoglycemia as a cause.

**Why Each Wrong Option is Incorrect:**
A. Hypoglycemia (Option A) is unlikely due to normal plasma glucose levels.
B. Hyperglycemia (Option B) is also unlikely as the CSF glucose level is low, not high.
C. Brain infections (Option C) may present with low CSF glucose levels, but the most common cause of low CSF glucose is brain tumors, not infections.

**Clinical Pearl:**
In children presenting with seizures and low CSF glucose levels, it is essential to consider the possibility of a brain tumor, even in the absence of systemic factors (hypoglycemia) or local factors (hyperglycemia). A low CSF glucose level indicates increased brain cell activity, and a brain tumor is the most common cause of this phenomenon.