• Perform a complete neurologic exam, including a mental status exam

Look for Signs of Meningeal Irritation:

Neck Stiffness

• Examine the neck for rigidity by gentle forward flexion with the patient in supine position

Kernig Sign

• Position of patient: Supine with the hip flexed at 90^o
• Positive when extension of the knee from this position elicits resistance or pain in the lower back or posterior thigh

Brudzinski Sign

• Position of patient: Supine
• Positive when passive neck flexion results in spontaneous flexion of the knees and hips

Contralateral Reflex

• Position of patient: Supine
• Positive when passive flexion of one hip and knee causes flexion of the contralateral leg

Look for Signs of Increased Intracranial Pressure (ICP)

• Altered level of consciousness (eg stupor or coma)
• Dilated, poorly reactive, or nonreactive pupils
• Ocular movement disorders (eg Abducens nerve palsy)
• Cushing reflex: Bradycardia, hypertension and irregular breathing
• Papilledema on fundoscopic exam
• Projectile vomiting
• Decerebrate posturing

Other Signs and Symptoms
Neonates

• Neonates with bacterial meningitis usually do not have meningismus
• They can present with temperature instability, jaundice, vomiting, diarrhea, respiratory distress, high-pitched crying, lethargy, refusal to eat and changes in affect and state of alertness
• Bulging fontanelle may occur late in the illness
• Seizures commonly reported among those with group B streptococcal meningitis

Children 1-4 years old

• Fever, chills, vomiting, photophobia, severe headache and nuchal rigidity are the most common initial symptoms

Elderly

• May present with lethargy or obtundation, no fever and variable signs of meningeal inflammation; they may also suffer antecedent or concurrent respiratory infections

• A diagnostic mainstay, perform a lumbar puncture (LP) promptly and send cerebrospinal fluid specimens for exams, to facilitate initiation of appropriate therapy
  • If signs of increased intracranial pressure or a mass are present, consider treating the condition first then do neuroimaging before doing lumbar puncture to decrease risk of brain herniation
• Cerebrospinal fluid formula: Cell count, glucose, protein

• Elevated opening pressure
• Neutrophilic pleocytosis
• Decreased glucose
• Elevated protein levels [100-500 mg/dL indicates injury to the blood-brain barrier (BBB)]
• Elevated lactate levels

• 10⁵ CFU/mL of bacteria should be present for Gram stain to be reliable

• Acid fast bacilli (AFB) smear and tuberculosis culture, India ink, cryptococcal antigen latex agglutination system (CALAS), latex antigen techniques, polymerase chain reaction (PCR), tissue culture, Limulus lysate test, counter immunoelectrophoresis

• Used to detect causative organism and establish susceptibility patterns when the cerebrospinal fluid cultures are negative or not available
• Obtain blood culture before instituting empiric antibiotic therapy is recommended

• Complete blood count (CBC), Fibrin degradation products (FDP)
• Urine osmolality and sodium (Na), plasma osmolality
• Blood sugar

• If a patient has the following: focal neurologic findings (excluding cranial nerve palsies), new-onset seizures, severely immunocompromised state, papilledema or presents with coma, perform a head computed tomography scan prior to doing a lumbar puncture to rule out the presence of intracranial mass lesions because of the potential risk for herniation
• Computed tomography prior to lumbar puncture is also recommended in immunocompromised patients human immunodeficiency virus (HIV), acquired immune deficiency syndrome (AIDS), patients on immunosuppressive therapy, after transplantation, patients with history of central nervous system disease and those with new-onset seizure within 1 week prior to presentation
• Blood cultures should be sent and empirical antimicrobial therapy should be initiated prior to computed tomography scan
  • Starting antimicrobial therapy 1-2 hours prior to lumbar puncture is not thought to decrease the diagnostic sensitivity of the cerebrospinal fluid study
  • Blood cultures, test for bacterial antigens and cerebrospinal fluid formula will still provide evidence for or against the presence of meningitis

• Magnetic resonance imaging with gadolinium enhancement and diffusion-weighted imaging may be used for patients with meningitis secondary to medical devices (eg cerebrospinal fluid shunt, cerebrospinal fluid drain, intrathecal drug therapy)