Infectious Disease · Central Nervous System Infections
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Enteroviruses (specifically Coxsackievirus, Echovirus, and Poliovirus) are the most common cause of viral meningitis in both children and adults.
Cerebrospinal fluid (CSF) analysis in viral meningitis typically reveals a lymphocytic pleocytosis, normal glucose levels, and mildly elevated protein.
The CSF glucose level is a critical differentiator, as it is characteristically low in bacterial and fungal meningitis but normal in viral meningitis.
Aseptic meningitis is the clinical term used when the patient presents with signs of meningeal irritation but routine bacterial cultures of the CSF are negative.
Herpes Simplex Virus type 2 (HSV-2) is a common cause of viral meningitis, particularly in patients presenting with a concurrent genital herpes outbreak.
West Nile virus should be suspected in patients presenting with viral meningitis accompanied by acute flaccid paralysis or movement disorders during summer months.
Empiric treatment for suspected meningitis must include vancomycin and ceftriaxone until bacterial meningitis is definitively ruled out by CSF analysis.
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A 22-year-old male presents to the emergency department with a 2-day history of fever, headache, and nuchal rigidity. He denies any recent travel or sick contacts. On physical examination, he is alert and oriented with a positive Kernig sign and positive Brudzinski sign. A lumbar puncture is performed, and CSF analysis shows a white blood cell count of 150/µL with 90% lymphocytes, a glucose of 65 mg/dL, and a protein of 45 mg/dL.
What is the most likely diagnosis?
Viral meningitis
The patient's clinical presentation of meningeal signs combined with a CSF profile showing lymphocytic pleocytosis and normal glucose is classic for viral meningitis, which is supported by the 'normal glucose' bet.
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Etiology / Epidemiology
Most common cause is Enterovirus (Coxsackie, Echovirus). Affects children/young adults primarily.
Clinical Manifestations
Presents with fever, headache, and nuchal rigidity. Kernig's and Brudzinski's signs are positive.
Diagnosis
Lumbar puncture is the gold standard. CSF shows lymphocytic pleocytosis and normal glucose.
Treatment
Management is supportive care. Avoid antibiotics until bacterial meningitis is ruled out.
Prognosis
Excellent prognosis with full recovery in 7-10 days. Rare neurological sequelae.
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Epidemiology & Etiology
Enteroviruses account for >85% of cases, typically via fecal-oral or respiratory spread. Other common pathogens include Arboviruses (West Nile) and HSV-2. Incidence peaks in summer and fall months.
Pertinent Anatomy
Inflammation involves the leptomeninges (arachnoid and pia mater). The blood-brain barrier is breached, allowing inflammatory cells into the subarachnoid space.
Pathophysiology
Viral invasion triggers an inflammatory response, increasing intracranial pressure. Unlike bacterial meningitis, the blood-brain barrier remains relatively intact, preventing massive protein leakage.
Clinical Manifestations
Patients present with the classic triad of fever, headache, and stiff neck. Look for Kernig's sign (pain with knee extension) and Brudzinski's sign (neck flexion causing hip flexion). Altered mental status or seizures suggest encephalitis rather than simple meningitis.
Diagnosis
Lumbar puncture is mandatory. CSF analysis reveals lymphocytic pleocytosis (10-1000 cells/µL), normal glucose (45-80 mg/dL), and mildly elevated protein. CSF PCR is the diagnostic test of choice for viral identification.
Treatment
Treatment is supportive care including IV fluids, antipyretics, and analgesics. Empiric antibiotics (e.g., Ceftriaxone + Vancomycin) must be continued until bacterial cultures are negative. Acyclovir is indicated if HSV is suspected.
Prognosis
Most patients achieve full recovery within 1-2 weeks. Long-term morbidity is rare, though some patients report persistent headaches or fatigue.
Differential Diagnosis
Bacterial Meningitis: CSF shows low glucose and high neutrophils
Fungal Meningitis: Often immunocompromised with very low CSF glucose
Encephalitis: Presence of altered mental status or focal deficits
Subarachnoid Hemorrhage: Sudden onset 'thunderclap' headache
Brain Abscess: Focal neurological deficits and ring-enhancing lesion on CT