Meningitis and Encephalitis

Meningitis and encephalitis are inflammatory disorders of the central nervous system and are among the most important causes of secondary headache, in which the head pain is a symptom of serious underlying disease. Meningitis is inflammation of the meninges, the membranes covering the brain and spinal cord, and classically presents with headache, fever, and neck stiffness. Encephalitis is inflammation of the brain itself, marked by altered consciousness or behaviour, seizures, or focal neurological signs. The two can overlap as meningoencephalitis, and both can be medical emergencies.

Definition

Meningitis is inflammation of the meninges surrounding the brain and spinal cord, most often infective, while encephalitis is inflammation of the brain parenchyma; when both meninges and brain are involved the term meningoencephalitis is used. As causes of headache they are secondary headaches, attributed to the underlying inflammatory or infective process rather than being primary disorders.

Scope

This entry orients the reader to meningitis and encephalitis as central nervous system infections and inflammatory syndromes that produce secondary headache, covering their defining features, the principal causes, the diagnostic role of cerebrospinal fluid examination, and why prompt recognition matters. It is a reference description and not a guide to diagnosis or treatment of any individual; no dosing or management protocols are given.

Core questions

• How do meningitis and encephalitis differ clinically?
• Why is headache with fever and neck stiffness treated as a possible emergency?
• What role does cerebrospinal fluid examination play in distinguishing causes?

Key concepts

• Meningeal versus parenchymal inflammation
• Meningoencephalitis
• Bacterial versus viral meningitis
• Herpes simplex and other viral encephalitides
• Cerebrospinal fluid analysis via lumbar puncture
• Secondary headache with systemic and neurological features
• Autoimmune (non-infective) encephalitis

Mechanisms

In meningitis, pathogens or other inflammatory triggers provoke inflammation of the meninges and the cerebrospinal fluid space, irritating pain-sensitive structures and producing headache, neck stiffness, and signs of meningeal irritation. In encephalitis, inflammation of the brain parenchyma, most often viral but sometimes autoimmune, disrupts cortical and subcortical function and gives rise to altered consciousness, behavioural change, seizures, or focal deficits. Examination of the cerebrospinal fluid obtained by lumbar puncture is central to characterising the inflammatory response and narrowing the likely cause, with distinct patterns suggesting bacterial, viral, or other origins.

Clinical relevance

Meningitis and encephalitis are key secondary causes that headache evaluation must not miss, because the combination of headache with fever, altered mental status, neck stiffness, or new neurological signs can indicate a life-threatening central nervous system infection. This entry describes the syndromes and their evaluation for reference and evidence-appraisal purposes; it does not provide individualised diagnostic or treatment guidance, and recognition of suspected cases calls for urgent professional assessment.

Epidemiology

Acute bacterial meningitis remains a serious cause of morbidity and mortality despite advances in care, with a limited number of bacterial species responsible for most community-acquired cases in adults. Viral causes account for many cases of both aseptic meningitis and encephalitis, and herpes simplex virus is a particularly important cause of sporadic encephalitis because of its severity. Autoimmune mechanisms are increasingly recognised as a non-infective cause of encephalitis.

Evidence & guidelines

Clinical practice guidelines from the Infectious Diseases Society of America on bacterial meningitis (Tunkel and colleagues, 2004) and on encephalitis (Tunkel and colleagues, 2008), the European ESCMID guideline on acute bacterial meningitis (van de Beek and colleagues, 2016), and the International Encephalitis Consortium consensus on case definitions (Venkatesan and colleagues, 2013) provide the principal frameworks for diagnosis and classification.

History

Recognition of meningitis and encephalitis as distinct inflammatory disorders of the nervous system developed alongside the rise of microbiology and the introduction of lumbar puncture for cerebrospinal fluid examination, which transformed diagnosis. More recently, the description of antibody-mediated autoimmune encephalitis broadened the concept of encephalitis beyond infection and prompted consensus efforts to standardise case definitions.

Debates

How should encephalitis be defined and classified across infective and autoimmune causes?

The growing recognition of autoimmune encephalitis alongside classic viral causes created a need for standardised case definitions and diagnostic algorithms, which the International Encephalitis Consortium addressed to improve consistency in research and surveillance.

Seminal works

• van-de-beek-2006
• tunkel-2008
• venkatesan-2013

Frequently asked questions

What is the difference between meningitis and encephalitis?

Meningitis is inflammation of the membranes (meninges) covering the brain and spinal cord and classically causes headache, fever, and neck stiffness. Encephalitis is inflammation of the brain tissue itself and tends to cause altered consciousness, confusion, seizures, or focal neurological signs. When both occur together the term meningoencephalitis is used.

Why is a headache with fever and a stiff neck treated as urgent?

Because that combination can indicate meningitis or encephalitis, which are potentially life-threatening central nervous system infections. Prompt evaluation, often including cerebrospinal fluid examination, is important; this entry is a reference description and not a substitute for urgent medical assessment.