Meningitis

Introduction

• CNS infections may be caused by a variety of bacteria, fungi, viruses, and parasites. The most common causes of bacterial meningitis are Streptococcus pneumoniae, group B Streptococcus, Neisseria meningitidis, Haemophilus influenzae, and Listeria monocytogenes,
• The critical first step in the acquisition of acute bacterial meningitis is nasopharyngeal colonization of the host by the bacterial pathogen. The bacteria first attach themselves to nasopharyngeal epithelial cells and are then phagocytized into the host’s bloodstream.
• A common characteristic of most CNS bacterial pathogens (eg, H. influenzae, Escherichia coli, and N. meningitidis) is the presence of an extensive polysaccharide capsule that is resistant to neutrophil phagocytosis and complement opsonization.

Clinical Presentation

• Meningitis causes CSF fluid changes, and these changes can be used as diagnostic markers of infection.
• Clinical presentation varies with age; generally, the younger the patient, the more atypical and the less pronounced is the clinical picture.
• Patients may receive antibiotics before a diagnosis of meningitis is made, delaying presentation to the hospital. Prior antibiotic therapy may cause the Gram stain and CSF culture to be negative, but the antibiotic therapy rarely affects CSF protein or glucose.
• Classic signs and symptoms include fever, nuchal rigidity, altered mental status, chills, vomiting, photophobia, and severe headache. Kernig and Brudzinski signs may be present but are poorly sensitive and frequently absent in children.
• Clinical signs and symptoms in young children may include bulging fontanelle, apneas, purpuric rash, and convulsions, in addition to those just mentioned.

Signs and Symptoms and Diagnosis

• Purpuric and petechial skin lesions typically indicate meningococcal involvement, although the lesions may be present with H. influenzae meningitis. Rashes rarely occur with pneumococcal meningitis.
• Bacterial Meningitis Score is a validated clinical decision tool aimed to identify children older than 2 months with CSF pleocytosis who are at low risk of ABM. This tool incorporates clinical features such as positive CSF Gram stain, presence of seizure, serum absolute neutrophil count of 10,000 cells/mm 3 or more (≥10 × 109 /L), CSF protein ≥80 mg/dL (≥800 mg/L), and CSF neutrophil count ≥1000 cells/mm3 (≥1 × 109 /L). Treatment is recommended when one or more criteria are present. An elevated CSF protein of 50 mg/dL or more and a CSF glucose concentration less than 50% of the simultaneously obtained peripheral value suggest bacterial meningitis (see Table 36–1).
• The values for CSF glucose, protein, and WBC concentrations found with bacterial meningitis overlap significantly with those for viral, tuberculous, and fungal meningitis (see Table 36–1) and cannot always distinguish the different etiologies of meningitis.
• Gram stain and culture of the CSF are the most important laboratory tests performed for bacterial meningitis. When performed before antibiotic therapy is initiated, Gram stain is both rapid and sensitive and can confirm the diagnosis of bacterial meningitis in 75% to 90% of cases.
• Polymerase chain reaction (PCR) techniques can be used to diagnose meningitis caused by N. meningitidis, S. pneumoniae, and H. influenzae type b (Hib). Latex fixation, latex coagglutination, and enzyme immunoassay tests provide for the rapid identification of several bacterial causes of meningitis, including S. pneumoniae, N. meningitidis, and Hib. The rapid antigen tests should be used in situations in which the Gram stain is negative.
• Diagnosis of tuberculosis meningitis employs acid-fast staining, culture, and PCR of the CSF.

Management

Pyogenic Meningitis Antibiotic therapy must be started as soon as possible, after the diagnosis is suspected clinically, as delay in starting the treatment increases morbidity.

• This is especially so in meningococcal meningitis. If possible, take CSF before starting antibiotic, but do not delay the treatment. (The first doctor who comes across such a patient in a PHC or in general practice must give Benzyl Penicillin IV and chloramphenicol IV, after taking the blood sample for culture when possible) Dose Benzyl Penicillin 20 L units IV 2 hrly + × 2 weeks Chloramphenicol 1 gm IV 6th hrly × 2 weeks.
• Empiric Therapy of CommunityAcquired Bacterial Meningitis in Adults When the organism is not isolated from the CSF—must include either Penicillin G or a 3rd generation cephalosporin.
• In our institution, we treat the above category of patients with penicillin G and chloramphenicol which will cover H.influenzae infection also. In the older age group patients (i.e., > 50yr): Empirical therapy is: Inj. Ceftriaxone 2 gm IV 12 hrly × 2 weeks Or Inj. Cefotaxime 2 gm IV 4th hrly × 2 weeks + Inj. Ampicillin 2 gm IV 4th hrly × 2 weeks Or Inj. Penicillin G 20 L units IV 2 hrly × 2 weeks

Role of Corticosteroids in Meningitis The role of corticosteroids in reducing raised intracranial tension is still controversial and remains unresolved. Though the use of corticosteroid in reducing sequelae of meningitis is receiving support from various studies, its routine use in the treatment of bacterial meningitis is not at all justifiable