Acute And Chronic Meningitis Health Article

Introduction

Meningitis is the most common serious manifestation of infection of the central nervous system (CNS). Inflammatory involvement of the subarachnoid space with meningeal irritation leads to the classic triad of headache, fever and meningism, and to a pleocytosis in the cerebrospinal fluid (CSF). Meningitis is divided clinically into acute and chronic disease; acute meningitis develops over hours or days, whereas the symptoms of chronic meningitis evolve over weeks or even months.

Acute meningitis is caused by a variety of infectious agents (Table 22.1). The most serious form of acute meningitis is caused by pyogenic bacteria, such as Streptococcus pneumoniae , Neisseria meningitidis , Haemophilus influenzae . ^{1, 2, 3} Group B streptococci ( Streptococcus agalactiae ), Enterobacteriaceae and Listeria monocytogenes are the major pathogens in the neonatal period (Table 22.2). ^{3, 4}

Patients who have aseptic meningitis show signs of meningeal inflammation and CSF pleocytosis with predominance of lymphocytes, but no bacterial pathogen can be isolated from CSF or blood. The term 'aseptic meningitis' predates the routine use of tests to detect viruses and other difficult to culture organisms and includes cases caused by highly diverse etiologic agents. Many cases of aseptic meningitis are caused by viruses, primarily enteroviruses (Table 22.3), including Coxsackie viruses. Nonviral causes of aseptic meningitis include spirochetes, rickettsiae, Mycobacterium tuberculosis , Leptospira spp., Brucella spp., fungi and noninfectious etiologies (see Table 22.1). ⁵ While signs and symptoms overlap between bacterial and aseptic meningitis, the latter has a much more favorable prognosis, particularly when caused by viruses.

Chronic meningitis is defined by symptoms of meningeal inflammation with CSF pleocytosis that persist for more than 4 weeks. ⁵ The diagnosis is based on the history, clinical evidence of meningitis, CSF examination, and often on imaging studies. ⁶ The differential diagnosis is broad (see Table 22.1). The predominant CSF cell type can provide clues to the underlying disease (Table 22.4).