**Core Concept**
Tuberculous meningitis (TBM) is a severe infection of the central nervous system (CNS) caused by Mycobacterium tuberculosis. The disease leads to inflammation of the meninges, the protective membranes surrounding the brain and spinal cord. Characteristic changes in cerebrospinal fluid (CSF) are a key diagnostic feature of TBM.

**Why the Correct Answer is Right**
The classical CSF finding in TBM is characterized by an elevated protein level, decreased glucose concentration, and increased lymphocyte count. The elevated protein level is due to the breakdown of the blood-brain barrier and the influx of inflammatory cells into the CSF. The decreased glucose level is a result of the consumption of glucose by the bacteria and the inflammatory cells. The increased lymphocyte count is indicative of an adaptive immune response to the infection. This combination of findings is highly suggestive of TBM and can aid in the diagnosis.

**Why Each Wrong Option is Incorrect**
**Option B:** Incorrect because TBM is characterized by decreased glucose levels, not increased levels.
**Option C:** Incorrect because TBM is associated with increased protein levels, not decreased levels.
**Option D:** Incorrect because TBM is characterized by lymphocytic pleocytosis, not neutrophilic pleocytosis.

**Clinical Pearl / High-Yield Fact**
In TBM, the CSF protein level can be as high as 1-2 g/dL, and the glucose level can be as low as 30-40% of the normal serum glucose level. A lymphocyte count of more than 50% of the total white cell count is highly suggestive of TBM.

**✓ Correct Answer: A. Increased protein, decreased sugar, increased lymphocytes**