## CSF Profile in GBS: Albuminocytologic Dissociation **Key Point:** The hallmark CSF finding in Guillain-Barré Syndrome is **albuminocytologic dissociation** — markedly elevated protein (often >100 mg/dL, can exceed 1000 mg/dL) with normal or only mildly elevated cell count (<10 cells/μL, predominantly lymphocytes). ### CSF Findings in GBS | Parameter | Finding | Notes | | --- | --- | --- | | **Protein** | Markedly elevated (100–1000 mg/dL) | Rises progressively over first 1–2 weeks | | **Cell count** | Normal to mildly elevated (<10/μL) | Predominantly lymphocytes; neutrophils rare | | **Glucose** | Normal (serum:CSF ratio normal) | Distinguishes from bacterial meningitis | | **Culture** | Sterile | Rules out infectious meningitis | | **Timing** | May be normal in first week | Protein rises as illness progresses | **Mnemonic:** **"Protein UP, Cells DOWN"** = Albuminocytologic dissociation = GBS ### Why This Pattern Occurs 1. **Protein elevation:** Increased vascular permeability at blood-nerve barrier → protein leakage into CSF 2. **Cell sparing:** Peripheral nerve inflammation does not directly seed CSF with inflammatory cells (unlike CNS meningitis) 3. **Progressive rise:** Protein typically peaks by week 2–3 of illness **High-Yield:** Early in the disease (first 48 hours), CSF may be **completely normal** — a normal CSF does NOT exclude GBS. Serial lumbar puncture may show the classic dissociation if clinical suspicion remains high. **Clinical Pearl:** If CSF shows marked pleocytosis (>50 cells/μL) or positive cultures, think of alternative diagnoses: bacterial meningitis, viral meningitis, Lyme disease, or HIV-associated polyradiculopathy. 
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