Clinical Features

SIGNS AND SYMPTOMS Definitive diagnosis is based on demonstrating bacterial organisms in the subarachnoid space along with a corresponding inflammatory response. The possibility of meningitis must be considered if the diagnosis is to be made. In classic and fulminant cases, about 25 percent of adult cases, there is little diagnostic challenge. The patient presents with rapidly developing fever, headache, stiff neck, photophobia, and altered mental status. Seizures occur in 25 percent of adults and at least that many children. In some patients, typically the very young and the elderly, the clinical features are nonspecific.

Certain historic data should increase the suspicion of meningitis and suggest specific pathogens. Several areas deserve special attention: living conditions, trauma, immunocompetence, immunization history, and antibiotic use. Army barracks and college dormitories are typical environments in which clusters of cases due to N. meningitidis occur. Day-care centers may become a source for multiple cases due to H. influenzae type b. A history of head trauma (S. pneumoniae) or neurosurgery (staphylococcal species or gram-negative rods) may be significant. Conditions that affect immunocompetence (e.g., history of surgical or functional splenectomy, glucocorticoid therapy, and HIV) should be sought. On the other hand, a history of immunization to H. influenzae type b in the past will make meningitis due to this organism unlikely. It is important to inquire about recent exposure to antibiotics, which may influence the clinical course, and CSF findings.

Examination must include assessment for meningeal irritation with resistance to passive neck flexion, Brudzinski sign (flexion of hips and knees in response to passive neck flexion), and Kernig sign (contraction of hamstrings in response to knee extension while hip is flexed). Examination of the skin is also crucial for seeking the purpuric rash characteristic of meningococcemia and, less commonly, other pathogens. Cutaneous stigmata suggesting microembolization (e.g., petechiae, splinter hemorrhages, and pustular lesions) should be aspirated when possible for Gram stain and culture. Paranasal sinuses should be percussed, and ears examined for evidence of primary infection. Fundi must be assessed for papilledema or absence of venous pulsation, indicating increased intracranial pressure. Neurologic examination should seek evidence of focal neurologic dysfunction, such as disordered eye movements, homonymous visual field deficits, facial asymmetry, and hemiparesis.45

LUMBAR PUNCTURE Blood cultures (two specimens drawn 15 min apart) yield the responsible organism in about 50 percent of cases of bacterial meningitis, but CSF analysis is paramount. Appropriate sequencing of LP, cranial imaging studies, and initiation of empirical antibiotics are further discussed below. However, LP should be carried out as quickly as possible.

LP should be performed if intracranial mass lesions and coagulopathy are unlikely on historical or clinical grounds. Specifically, patients with coma, papilledema, or focal neurologic findings require cranial imaging before LP. Prior to imaging, blood cultures should be obtained and empiric antibiotic therapy should be instituted. LP can then proceed if no intracranial mass lesion or mass effect exists. Antibiotic therapy given up to 2 h prior to lumbar puncture will not decrease the diagnostic sensitivity if CSF bacterial antigens assays are obtained along with CSF culture. 6

Local anesthetic should be used to improve patient comfort, relaxation, and cooperation. Anxiolitics such as benzodiazapines, which are helpful adjuncts in the performance of painful procedures, can cloud the patient's sensorium and confuse subsequent clinical assessment. The L3-L4 interspace should be punctured (L4-L5 in newborn infants) while the patient is curled as tightly as possible in a fetal position. In adults, a line drawn between the iliac crests crosses the spine at the L3-L4 interspace. Alternatively, the patient may be seated on the edge of a bed or cart leaning over a tray stand. The latter technique is particularly useful when landmarks are uncertain, as they may be in an obese patient. The site should be prepared with povidone-iodine and allowed to dry thoroughly to avoid introduction by

1 1 puncture and the production of chemical arachnoiditis. A 2 2;-in. 22-gauge needle should be used in children and a 3 2;-in. 20-gauge needle in adults. Although useful, the opening pressure is not critical for interpretation of the procedure. To obtain meaningful results, the pressure must be measured with the patient lying extended on his or her side. Pressures measured with the patient still curled in extreme flexion or while sitting will be artificially elevated. Normal pressure is less than 170 mm-H2O. Careful repositioning (straightening the curled patient or helping the seated patient to a lying position on his or her side) is safely performed with the needle in situ.

Four tubes, each containing at least 1 mL of CSF, are typically obtained. More volume —up to 5 mL—may be preferable in patients who are immunocompromised. Red and white blood cell counts with differential counts are requested for tubes 1 and 4. The two-tube assessment helps detect a traumatic tap because the rate of bleeding changes rapidly, causing a difference in red blood cell count between the two tubes. Tube 4 may also be used for culture and Gram stain. Tube 2 is sent for determination of protein and glucose levels. Tube 3 should be saved for other studies, discussed below, if necessary. Closing pressure is not necessary. 7

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