Meningitis

Introduction - Meningitis is an inflammatory disease of the leptomeninges, the tissues surrounding the brain and spinal cord, and is defined by an abnormal number of white blood cells in the cerebrospinal fluid.

Clinical Manifestations - Patients with bacterial meningitis are often so ill that they will present soon after symptom onset. The classic triad of acute bacterial meningitis consists of fever, nuchal rigidity, and a change in mental status. The headache is another common symptom and is usually worse than the patients usual headache. Nuchal rigidity can be demonstrated by the following physcial examiniation techniques.

• Brudzinski sign (figure B) - spontaneous flexion of the hips during attempted passive flexion of the neck.
•  Kernig sign (figure A) - inability or reluctance to allow full extension of the knee when the hip is flexed 90 degrees.

Aseptic meningitis often has a similar presentation to bacterial meningitis (eg, fever, headache, altered mental status, stiff neck, photophobia), which can be a life-threatening illness. However, in contrast to bacterial meningitis, the majority of patients with aseptic meningitis have a self-limited course that will resolve without specific therapy. In my experience, patients with bacterial meningitis are very sick and will seek medical attention quickly after the onset of symptoms.

Diagnosis - Lumbar puncture!!! Examination of the cerebrospinal fluid is crucial for establishing the diagnosis of bacterial meningitis. There are situations where you need to get a CT of the head before you get an LP. CT of the head is indicated if the patient has one or more of the following...

• Immunocompromised state (eg, HIV infection, immunosuppressive therapy, solid organ or hematopoietic stem cell transplantation)
• History of central nervous system (CNS) disease (mass lesion, stroke, or focal infection)
• New onset seizure (within one week of presentation)
• Papilledema or any signs of raised intracranial pressure
• Abnormal level of consciousness
• Focal neurologic deficit

If LP is delayed needs to be delayed while the patient is getting a CT of the head, blood cultures should be obtained and antimicrobial therapy should be administered empirically before the patient goes for the CT and the LP should be done as soon as possible when the patient is cleared from the CT of the head. Dexamethasone may be given before or at the same time as the antimicrobials if the labs and clinical picture is highly suspicious of bacterial meningitis. Empiric antibiotics will not effect the cytology of the CSF but it may effect the gram stain and culture.

CSF Analysis

Opening pressure -The opening pressure is typically elevated in patients with bacterial meningitis (>200 mmH2O).

False-positives - It is important to note that a false-positive elevation of the CSF white blood cell count can be found after traumatic lumbar puncture or in patients with intracerebral or subarachnoid hemorrhage in which both red blood cells and white blood cells are introduced into the subarachnoid space. Generalized seizures may also induce a transient CSF pleocytosis mainly neutrophils.
A Gram stain of the CSF should be obtained whenever there is suspicion of bacterial meningitis. It has the advantage of suggesting the bacterial etiology one day or more before culture results are available .

•  Gram-positive diplococci suggest pneumococcal infection
• Gram-negative diplococci suggest meningococcal infection
• Small pleomorphic gram-negative coccobacilli suggest Haemophilus influenzae infection
• Gram-positive rods and coccobacilli suggest Listeria infection

 Treatment

If the patient has no immunodeficiency

Ceftriaxone or Cefotaxime - 2 g IV every 12 hours

PLUS

Vancomycin - 15 to 20 mg/kg IV every 8 to 12 hours

PLUS

Ampicillin (in adults greater than 50yrs of age) - 2 g IV every four hours

If the patient has an immunodeficiency

Vancomycin - 15 to 20 mg/kg IV every 8 to 12 hours

PLUS

Ampicillin - 2 g IV every four hours

PLUS

Cefepime/Meropenem - 2 g IV every eight hours


If the patient is allergic to Beta-Lactams

Vancomycin - 15 to 20 mg/kg IV every 8 to 12 hours

PLUS

Moxifloxacin -  400 mg IV once daily

PLUS

Trimethroprim-Sulfamethoxazole (if the patient is older than 50 years of age and needs covereage for Listeria) - 5 mg/kg IV every 6 to 12 hours