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Meningitis and Its Mimics in Critical Care
Burke A. Cunha
Infectious Disease Division, Winthrop-University Hospital, Mineola, New York,
and State University of New York School of Medicine, Stony Brook, New York, U.S.A.Leon Smith
Department of Medicine, St. Michael’s Medical Center, Newark, New Jersey, U.S.A.INTRODUCTION
There are several diagnostic difficulties in patients presenting with the possibility of acute
bacterial meningitis (ABM). Critically ill patients with meningitis are usually transferred to the
critical care unit (CCU) for intensive supportive care. Meningitis may be mimicked by a variety
of infectious and noninfectious disorders. The mimics of meningitis are readily ruled out on
the basis of the history/physical exam and, if any doubt remains, then a lumbar puncture with
cerebrospinal fluid (CSF) analysis will include or exclude the diagnosis of ABM. Early and
appropriate empiric antimicrobial therapy of ABM in the CCU may be lifesaving. In contrast to
differential of diagnostic problem of encephalitis in the CCU, ABM in the CCU is not usually a
diagnostic problem but is primarily a therapeutic problem.
ABM is primarily caused by bacterial neuropathogens. It occurs in normal and
compromised hosts and may be acquired naturally or as a complication of open head trauma
or neurosurgical procedures. Regardless of the pathogen or mode of acquisition, the definitive
diagnosis of ABM rests on analysis of the CSF profile and Gram stain/culture of the CSF. In
normal and compromised hosts, ABM presents clinically with meningeal irritation, i.e., nuchal
rigidity. Nuchal rigidity must be differentiated from other causes of neck stiffness, i.e.,
meningismus associated with the mimics of meningitis. There are relatively few nonbacterial
causes of meningitis, and it is important to differentiate aseptic or viral meningitis from
bacterial meningitis. In general, patients with aseptic or viral meningitis are less critically ill
than are those with ABM. Patients ill enough to be admitted to the CCU usually are more likely
to have bacterial versus viral meningitis. Aseptic viral meningitis may be diagnosed by
analysis of the CSF profile, as well as specific viral culture/PCR determinations. Patients with
acute meningitis, either bacterial or viral, will have various degrees of nuchal rigidity with
intact mental status. Patients with mental confusion, i.e., encephalopathy, have encephalitis
and these patients do not have nuchal rigidity. Central nervous system (CNS) infection caused
by a few organisms, i.e., herpes simplex virus (HSV)-1,Mycoplasma pneumoniae, Listeria
monocytogenes,may present with a combination of stiff neck and mental confusion, i.e.,
meningoencephalitis. Any patient with fever and otherwise unexplained neck stiffness should
have a lumbar puncture performed to confirm the diagnosis of ABM. If ABM is suspected,
lumbar puncture should be performed prior to head CT/MRI scanning (1–6).
Therefore, the challenge of meningitis in the CCU setting is to arrive at a correct
diagnosis by ruling out the noninfectious mimics of meningitis, and then differentiating viral
meningitis from bacterial meningitis. Patients with signs of meningeal irritation and mental
confusion, i.e., meningoencephalitis, are diagnosed on the basis of the CSF profile and extra-
CNS signs, symptoms, and/or laboratory abnormalities. The objective of arriving at a
presumptive diagnosis of ABM is to begin appropriate empiric therapy as soon as possible.
Appropriate empiric therapy for ABM is determined by predicting the likely range of
pathogens. In ABM, the most likely pathogen is determined by the age of the patient, mode of
onset, epidemiological history/predisposing factors, physical signs, e.g., rash, rhinorrhea, and
cranial nerve abnormalities, and specific host defense defects and associated underlying
disorders, and the morphology/arrangement of organisms seen on the Gram stain of the CSF
(1–7).