A 35-year-old woman with fever, headache, and photophobia is admitted to hospital. CSF shows 1,200 cells/μL (90% neutrophils), protein 380 mg/dL, glucose 32 mg/dL (serum 105 mg/dL), and Gram-positive cocci in clusters are seen. Blood cultures are pending. Which clinical finding best distinguishes meningococcal meningitis from pneumococcal meningitis?

Explanation

## Discriminating Feature: Petechial/Purpuric Rash **Key Point:** The presence of a petechial or purpuric rash is the most specific clinical discriminator between meningococcal and pneumococcal meningitis. Meningococcemia (Neisseria meningitidis) characteristically produces a non-blanching petechial or purpuric rash, whereas pneumococcal meningitis (Streptococcus pneumoniae) rarely presents with a rash. ### Rash Pathophysiology Meningococcal sepsis causes: - Endothelial invasion and vasculitis - Disseminated intravascular coagulation (DIC) - Petechial hemorrhages (non-blanching) - Rapid progression to purpura fulminans in severe cases Pneumococcal disease typically causes meningitis without bacteremia-associated rash. ### Comparison Table: Meningococcal vs Pneumococcal Meningitis | Feature | Meningococcal | Pneumococcal | | --- | --- | --- | | **Rash** | Petechial/purpuric (60–80%) | Absent (< 5%) | | **Gram Stain** | Gram-negative diplococci | Gram-positive diplococci | | **Epidemiology** | Epidemic potential, young adults | Sporadic, elderly/asplenic | | **Sepsis** | Often present with meningitis | Meningitis may be sole presentation | | **CSF Glucose** | < 40% of serum (variable) | < 40% of serum (typical) | | **CSF Protein** | 100–500 mg/dL | 100–500 mg/dL | | **Prognosis** | Better with early antibiotics | Higher mortality if delayed | **Clinical Pearl:** A patient with meningitis AND a non-blanching petechial rash should be treated immediately for meningococcal sepsis — do not wait for lumbar puncture or culture results. This is a medical emergency. **High-Yield:** The **mnemonic RIPE** helps recall meningococcal sepsis features: - **R**ash (petechial/purpuric) - **I**ntense headache - **P**etechiae on extremities - **E**ndotoxemia (shock) **Warning:** Do not assume the absence of a rash excludes meningococcemia — up to 20% of meningococcal meningitis cases lack a rash. Conversely, a rash in a patient with meningitis is meningococcal until proven otherwise. **Tip:** Gram stain morphology (Gram-negative diplococci vs Gram-positive diplococci) is also discriminatory but requires microscopy expertise. The rash is a bedside clinical sign that requires no laboratory confirmation. [cite:Harrison 21e Ch 383]