■ Mycobacterium tuberculosis(uncommon)
■ Group B streptococcus, Escherichia coliandListeria monocytogenesare
the most common bacterial causes in neonates <1 month.
■ Streptococcus pneumoniae, Staphylococcus aureus, Pseudomonas aerugi-
nosaand coliform bacteria are common following neurosurgical proce-
dure or head trauma.
■ Viral
■ Enteroviruses (most common, increased in summer months)
■ Herpes simplex virus should always be suspected.
■ Numerous other viruses
■ Fungal (eg, Cryptococcus) and parasitic (eg, Toxoplasma gondii)—in the
immunocompromised
■ Noninfectious
■ SLE
■ Vasculitis
■ Drug induced
■ Carcinomatosis
■ Sarcoidosis
■ Behçet disease
A significant overlap exists between bacterial and viral meningitis presenta-
tions. Viral meningitis is a diagnosis that can be made only after other more
serious pathogens have been excluded.
PATHOPHYSIOLOGY
■ Bacterial infection begins with nasopharyngeal colonization →hematoge-
nous spread (more likely with encapsulated organisms) →CNS infection.
■ Viruses enter through the skin or via respiratory, GI, or GU tracts.
■ Fungi primarily spread from pulmonary source.
■ Meningeal inflammatory response to foreign agent resulting in:
■ Increased permeability of blood brain barrier →increased CSF proteins
■ Decreased glucose transport →decreased CSF glucose levels
SYMPTOMS
■ Fever
■ Headache (most common)
■ Stiff neck (seen half the time)
■ Photophobia
■ Mental status changes or irritability (infants)
■ Vomiting
■ Seizures
■ Symptoms may be diminished/absent in immunocompromised, very young,
or elderly patients.
EXAM
■ Fever
■ Nuchal rigidity
■ Increased deep tendon reflexes (DTRs)
■ Altered mental status
■ Lateral gaze ophthalmoplegia
■ Petechial or purpuric rash (ominous sign)
■ Kernigs sign: Position the patient with hips and knees flexed. Extend the
knees. Flexion of neck or pain in neck is + sign.
NEUROLOGY