The clinical features seen in neonatal meningitis are usually indistinguishable from those of neonatal sepsis. The most prevalent clinical signs include temperature instability, irritability or lethargy and poor feeding or vomiting . Neurological manifestations are more commonly seen after a bacterial attack. Meningitis caused by group B streptococci may initially present with features of respiratory distress, accompanying a systemic illness. These findings become less common with an earlier age of onset.
Neurologic signs may include irritability, lethargy, hypotonia, muscle twitches, tremors and seizures. A more specific feature is paradoxical irritability, wherein consolation by parents irritates rather than comforts the affected neonate. Findings of a full or bulging fontanelle are not uncommon. Some patients may present with nuchal rigidity or hydrocephalus . Cranial nerve lesions, especially involving the oculomotor, abducens and facial nerve may be seen in a few children.
Ventriculitis is seen accompanying neonatal meningitis in a few children, especially in those afflicted with gram negative bacilli . Certain organisms (C. diversus, Cronobacter (previously Enterobacter) sakazakii) responsible for causing vasculitis along with meningitis may lead to brain cysts and abscesses. Brain abscesses may have raised intracranial tension as one of its first manifestations, thereby leading to an increase in head size and non-projectile vomiting.
Meningitis is associated with an increased risk of mortality in neonates and hence, there should be no delay in the workup of a neonate suspected of suffering from meningitis. A lumbar puncture is the gold standard test to be done in such neonates, even in the absence of neurological manifestations.
The major findings seen on cerebrospinal fluid (CSF) analysis include an elevated CSF protein, decreased CSF glucose and pleocytosis, with polymorphonuclear leucocytes dominating the picture in both bacterial and viral meningitis. All three parameters need to be normal for a diagnosis of meningitis to be excluded . Symptomatic neonates should also undergo a CSF culture for confirmation of the diagnosis. It has been found though, that 15-30% of CSF-proven cases have negative blood culture results .
Another modality with higher sensitivity and specificity rates to detect neonatal meningitis is the polymerase chain reaction (PCR) assay, that is being increasingly used to detect the presence of organisms such as group B streptococci, herpes simplex virus, enterovirus etc  .
Urinary latex particle agglutination (LGA) is another method designed to rapidly screen neonates for meningitis.
The neuroimaging study of choice is magnetic resonance imaging (MRI) that may help to locate the foci of infection, areas of edema, hemorrhage, infarction or abscesses. Follow-up scans may help evaluate the resolution of infection. Newer MRI techniques such as diffusion-weighted scans and diffusion tensor imaging are being used to note any white matter changes associated with neonatal meningitis .
Computed tomography (CT) scans may appear to be beneficial in patients posted for neurosurgery, whilst cranial ultrasonography may be useful to document ventricle size in hydrocephalus. Chest radiography and electroencephalography (EEG) studies may be done in some cases.