Chapter 199. Meningitis and Encephalitis

1. Is the classic triad of fever, headache, and stiff neck reliable for bacterial meningitis?

2. What signs and symptoms distinguish meningitis from encephalitis?

3. What is appropriate empiric antimicrobial therapy?

4. When should a CT scan be done before lumbar puncture?

5. What cerebrospinal fluid studies are essential, and which ones should be done if the initial studies do not yield a diagnosis?

6. When is MRI helpful in the diagnosis?

7. How soon can the patient be discharged, and how long to continue antimicrobial therapy?

8. When should a neurology consult be obtained?

Meningitis and encephalitis may be the most terrifying diseases in medicine. Bacterial meningitis and viral encephalitis may be rapidly fatal, even in healthy persons. Survivors may suffer lasting neurological sequelae, including memory loss and seizures. Cases of meningococcal meningitis spark great anxiety in both caregivers and casual contacts. Viral meningitis, by contrast, gives patients a bad headache and a stiff neck, but uneventful recovery is the rule.

In the United States, bacterial meningitis affects 1.5 to 2.0 per 100,000 population annually, viral meningitis approximately 14 per 100,000 annually, and encephalitis 7 per 100,000 annually. Encephalitis generally refers to viral encephalitis, although bacteria, parasites, spirochetes, and fungi may all cause encephalitis. In this chapter, encephalitis refers specifically to viral encephalitis.

Meningitis

Is the Classic Triad Reliable?

A 43-year-old woman presents with complaints of fever of 103°F, headache, nausea, vomiting, and photophobia. In the emergency department, she becomes increasingly lethargic.

The classic triad of meningitis is fever, headache, and stiff neck (nuchal rigidity). Patients with bacterial meningitis may also have an altered level of consciousness. Almost all patients with bacterial meningitis have at least two of these features, so the absence of all four makes bacterial meningitis unlikely. Patients may also complain of photophobia, nausea, and vomiting.

It is difficult, if not impossible, to exclude bacterial meningitis based on the physical examination. Findings may include nuchal rigidity (pain on passive flexion of the neck), Kernig's sign, and Brudzinski's sign. Kernig's sign is elicited with the patient in the supine position. The thigh is flexed on the abdomen with the knee flexed. Attempts to passively extend the leg cause pain when meningeal irritation is present. Brudzinski's sign is elicited with the patient in the supine position, and is positive when passive flexion of the neck results in flexion of the hips and knees. Patients with bacterial meningitis may also have focal neurological deficits or seizures.

Less than 50% of children with bacterial meningitis have nuchal rigidity. The possibility of bacterial meningitis should be considered in every child with fever, vomiting, photophobia, lethargy or altered mental status. Many cases of bacterial meningitis in children are preceded by upper respiratory tract infections or otitis media. Signs of meningitis in the neonate are nonspecific, and include irritability, lethargy, poor feeding, vomiting, diarrhea, temperature instability (fever or hypothermia), respiratory ...