Differential Diagnosis for CSF with Lymphocytic Predominance, High Protein, and Normal/High Glucose
The most likely diagnoses include viral encephalitis (especially HSV, VZV, and enteroviruses), partially treated bacterial meningitis, tuberculosis, listeriosis, brucellosis, and tickborne rickettsial diseases, with viral etiologies being most common when glucose is truly normal. 1
Primary Differential Considerations
Viral Encephalitis/Meningitis
- HSV encephalitis typically presents with moderate CSF pleocytosis (tens to hundreds of cells), mildly elevated protein, and normal CSF:plasma glucose ratio 1
- VZV, EBV, and CMV can produce similar CSF profiles, particularly in immunocompromised patients 1
- Enteroviruses are among the most common causes and should be tested via PCR in all suspected cases 1, 2
- These three viral groups (HSV 1&2, VZV, enteroviruses) account for 90% of cases with identified viral pathogens 1
Bacterial Infections with Atypical Presentations
- Tuberculosis meningitis classically shows lymphocytic predominance with markedly elevated protein, though glucose is typically very low 3
- Listeriosis can present with lymphocytic predominance rather than neutrophilic pleocytosis 1, 3
- Brucellosis may produce a similar lymphocytic CSF pattern 1
- Partially treated acute bacterial meningitis can shift from neutrophilic to lymphocytic predominance with antibiotic exposure 1, 3
Tickborne Rickettsial Diseases
- Rocky Mountain Spotted Fever (RMSF) and Human Monocytic Ehrlichiosis (HME) typically show pleocytosis with either polymorphonuclear or lymphocytic predominance 4
- Moderately elevated protein (100-200 mg/dL) and normal glucose levels are commonly observed 4
- These cannot be reliably distinguished from meningococcal infection based on CSF alone, necessitating empiric treatment for both when indicated 4
Other Important Considerations
- Scrub typhus can present with lymphocytic pleocytosis, slightly elevated protein, and normal glucose, sometimes with hemorrhagic features 5
- Primary diffuse leptomeningeal gliomatosis presents with chronic meningitis, markedly elevated protein, moderate mononuclear pleocytosis, and normal or low glucose 6
- Immune-related adverse events from checkpoint inhibitors can cause aseptic meningitis with elevated WBC (lymphocytic predominance) and/or elevated protein 7
Critical Diagnostic Distinctions
When Glucose is Truly Normal or High
A CSF glucose >2.6 mmol/L (>47 mg/dL) makes bacterial meningitis unlikely 3
- A CSF:plasma glucose ratio >0.66 is normal; bacterial meningitis typically shows ratio <0.36 3
- Always obtain simultaneous plasma glucose for accurate interpretation 1
CSF Lactate as Discriminator
- CSF lactate <2 mmol/L effectively rules out bacterial disease with 93-96% specificity 1, 2
- This test is most useful when obtained prior to antibiotic administration 3
Essential Workup Algorithm
Immediate CSF Testing
- PCR for HSV-1, HSV-2, VZV, and enteroviruses in all cases 1, 2
- Cell count with differential, protein, glucose (with simultaneous plasma glucose) 1
- Gram stain and bacterial culture 8
- CSF lactate if bacterial meningitis in differential 1, 2
Additional Testing Based on Clinical Context
- Mycobacterium tuberculosis testing (6 mL CSF) when chronic presentation or epidemiologic risk 1
- Fungal studies if immunocompromised 8
- Autoimmune encephalopathy panel and oligoclonal bands if ADEM or autoimmune etiology suspected 7, 9
- Cytology if concern for neoplastic meningitis 8
Common Pitfalls to Avoid
Early Disease Presentations
- 5-10% of HSV encephalitis cases have initially normal CSF with negative PCR 1
- If first CSF is normal but clinical suspicion remains high, repeat LP at 24-48 hours is likely to be abnormal 1
- Polymorphonuclear cells may predominate early in viral meningitis, especially enteroviral disease 3
Immunocompromised Patients
- May have acellular CSF despite active viral encephalitis (HSV, VZV, EBV, CMV) 1
- Maintain high index of suspicion regardless of cell count until cultures finalized 8
- Require expanded PCR testing including CMV, JC virus, West Nile virus, adenovirus 8