Meningitis%20-%20acute,%20bacterial Diagnosis

• 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

• Some patients may not present with the classic signs, eg alcoholics, patients who are immunocompromised and who had meningitis after surgery

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 LP promptly and send cerebrospinal fluid specimens for exams, to facilitate initiation of appropriate therapy
  • If signs of increased ICP or a mass are present, consider treating the condition first then do neuroimaging before doing LP to decrease risk of brain herniation (Please see Non-Pharmacological Therapy section)
  • Presence of the following should prompt delay in performing LP:
    • Presence of signs of severe sepsis or rapidly evolving rash
    • Respiratory or cardiac compromise
    • Treatment with an anticoagulant, antiplatelet, or if with known thrombocytopenia or clotting abnormality
    • Infection at lumbar puncture site
• CSF formula:
  • Cell count
  • Glucose <40 mg/dL
  • Protein >50 mg/dL

• Elevated opening pressure (>100-200 mmHg)
• Neutrophilic pleocytosis
• Decreased glucose levels (hypoglycorrachia) and CSF/serum glucose ratio
• 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
• Gram stain is a cheap and important tool for diagnosis, however, sensitivity varies by age group, type of pathogen and antibiotic used previously
• CSF culture is the gold standard in the diagnosis of bacterial meningitis, however, results may take time

Antigen/Antibody Tests

• Eg pneumococcal bacterial antigen tests (BAT), latex agglutination test, cryptococcal antigen latex agglutination system (CALAS), immunochromatographic antigen test
  • Make use of serum containing bacterial antibodies or commercially available antisera directed against capsular polysaccharides of meningeal pathogens
• BAT is reserved for patients whose initial CSF Gram stain is negative or CSF culture is negative after 48 hours of incubation
  • Pneumococcal BAT have a sensitivity for pneumococcal meningitis between 67-100% and a specificity of >95%
• Latex agglutination is a rapid diagnostic tool to determine the causative pathogen
  • Sensitivity varies for each causative pathogen: 78-100% for H influenzae, 22-93% for N meningitidis, and 59-100% for S pneumoniae
  • Sensitivity decreases when empiric treatment is started before lumbar puncture
• Rapid immunochromatographic antigen test (eg S pneumoniae BinaxNOW®) has 99-100% sensitivity and specificity for pneumococcal meningitis

• Acid-fast bacilli (AFB) smear and tuberculosis culture, India ink, polymerase chain reaction (PCR), tissue culture, Limulus lysate test, counter immunoelectrophoresis, metagenomic next-generation sequencing (mNGS)
• Multiplex PCR is a rapid, non-culture based method with sensitivity of 90% and specificity of 97%

• 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)
• C-reactive protein (CRP) and serum procalcitonin
• 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 CT scan prior to doing a lumbar puncture (LP) to rule out the presence of intracranial mass lesions because of the potential risk for herniation
• CT prior to LP 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 CT scan
  • Starting antimicrobial therapy 1-2 hours prior to LP is not thought to decrease the diagnostic sensitivity of the cerebrospinal fluid (CSF) study
  • Blood cultures, test for bacterial antigens and CSF formula will still provide evidence for or against the presence of meningitis

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