In a patient with a brain abscess caused by a KPC‑producing Klebsiella (polymerase chain reaction positive for blaKPC) and a neutrophil‑predominant cerebrospinal fluid pleocytosis, could the lesion still represent primary central nervous system lymphoma?

Could It Still Be CNS Lymphoma?

No—a brain abscess caused by KPC-producing Klebsiella with neutrophil-predominant CSF pleocytosis is highly inconsistent with primary CNS lymphoma and effectively excludes this diagnosis in the clinical context described.

Why This Is Not CNS Lymphoma

Microbiological Confirmation Rules Out Lymphoma

• PCR-confirmed KPC-producing Klebsiella pneumoniae establishes a definitive bacterial etiology, and bacterial brain abscesses are fundamentally distinct from neoplastic processes like primary CNS lymphoma. 1
• Klebsiella brain abscesses are associated with high mortality, particularly when intraventricular spread occurs, and require urgent surgical drainage plus appropriate antibiotics—not the methotrexate-based chemotherapy used for lymphoma. 1

CSF Profile Is Incompatible with Lymphoma

• Primary CNS lymphoma typically presents with increased protein, normal or mildly decreased glucose, and a lymphocytic pleocytosis—not a neutrophil-predominant pattern. 2
• Neutrophil-predominant CSF pleocytosis is the hallmark of bacterial infection, including pyogenic brain abscesses caused by organisms like Klebsiella. 3
• CSF in PCNSL may show pleocytosis in approximately 51.5% of cases, but this is typically lymphocytic, and flow cytometry would detect monotypic B cells rather than neutrophils. 2, 4

Imaging and Clinical Context

• Ring-enhancing lesions occur in both bacterial abscesses and CNS lymphoma, but the clinical and laboratory context determines the diagnosis. 3, 5
• In bacterial abscesses, ring enhancement is typically thin and regular with significant surrounding edema, whereas primary CNS lymphoma more commonly shows homogeneous or thick irregular enhancement with less edema. 3, 6
• The presence of a positive bacterial culture from the lesion is definitive for abscess, regardless of imaging appearance. 1

Important Diagnostic Pitfalls to Avoid

EBV DNA Does Not Confirm Lymphoma in This Setting

• EBV DNA is detected in CSF of approximately 7–13% of HIV-infected individuals without lymphoma, and can be present in other CNS infections including bacterial abscesses. 3
• A positive EBV PCR in the setting of confirmed bacterial infection does not indicate concurrent lymphoma—it reflects viral shedding or reactivation in the context of systemic illness. 3

When Lymphoma Should Actually Be Considered

• Primary CNS lymphoma should be suspected when imaging shows periventricular or corpus callosum lesions with homogeneous enhancement, restricted diffusion on DWI, and CSF shows lymphocytic pleocytosis with monotypic B cells on flow cytometry. 2, 3, 5
• Stereotactic biopsy remains the gold standard when diagnosis is uncertain, but in your case the microbiological confirmation of Klebsiella makes biopsy for lymphoma unnecessary. 2, 7
• Corticosteroids must be avoided before biopsy if lymphoma is suspected, because they cause rapid tumor regression and render specimens nondiagnostic—but this caveat is irrelevant when bacterial infection is proven. 2, 8

Clinical Management Implications

• Treatment should focus on the confirmed bacterial abscess: prolonged intravenous antibiotics (typically 6–8 weeks) targeting KPC-producing Klebsiella, with consideration for repeat surgical drainage if clinical deterioration occurs. 1
• Monitor for complications including intraventricular rupture, cerebral edema, and septic shock, which are associated with high mortality in Klebsiella brain abscesses. 1
• Do not delay appropriate antibiotic therapy or surgical intervention by pursuing unnecessary workup for lymphoma when bacterial etiology is established. 1