Meningitis%20-%20acute,%20bacterial Diagnosis
Assessment
- 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 90o
- 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
Laboratory Tests
Lumbar Puncture and Cerebrospinal Fluid (CSF) Exams
- 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
- CSF 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
Antigen/Antibody Tests
- Eg pneumococcal 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
- Bacterial antigen tests (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
- Acid-fast bacilli (AFB) smear and tuberculosis culture, India ink, 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
Imaging
Head Computed Tomography (CT) Scan
- 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 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)