Meningitis

Meningitis (from the Latin meningitis) is an inflammation of the meninges that line the brain and spinal cord. This condition is considered an emergency in neurology and infectious disease medicine. If not treated in a timely manner, it can lead to severe complications, disability, and even death.

The inflammatory process in meningitis involves the subarachnoid space, leading to changes in the composition of the cerebrospinal fluid (CSF). Depending on the nature of these changes and the underlying etiology, meningitis is classified as purulent (most often bacterial) or serous (most often viral).

Aetiology and Pathophysiology

The cause of meningitis is an infectious agent that penetrates the central nervous system (CNS). The pathogen may enter the body via hematogenous (i.e., bloodstream) or contiguous (e.g., from otitis, sinusitis, or cranial trauma) routes.

Major groups of pathogens include:

• Bacteria: Responsible for the most severe, purulent forms. Key pathogens: Neisseria meningitidis (meningococcus), Streptococcus pneumoniae (pneumococcus), and Haemophilus influenzae type b.
• Viruses: Cause serous meningitis, which usually has a milder course. Common pathogens are enteroviruses, herpes simplex virus, and mumps virus.
• Fungi: Primarily affect individuals with immunodeficiency (e.g., Cryptococcus neoformans in HIV infection).

Once microorganisms enter the subarachnoid space, they trigger a vigorous inflammatory reaction. This leads to cerebral edema, increased intracranial pressure, and impaired microcirculation, which determine the severity of the condition.

Clinical significance

Diagnosis is based on a combination of systemic infectious and meningeal symptoms. The “gold standard” of diagnosis is lumbar puncture followed by CSF analysis, which reveals inflammatory changes (pleocytosis) and helps identify the causative pathogen.

Clinical manifestations cover three major syndromes:

1. Systemic infectious syndrome: Sudden onset, high fever (39–40 °C), chills, general weakness.
2. Meningeal syndrome: This is key for diagnosis.
   • Headache: Severe, bursting pain, not responsive to common analgesics.
   • Neck stiffness: Inability to passively flex the patient’s head and bring the chin to the chest.
   • Positive meningeal signs: Kernig’s and Brudzinski’s signs.
   • Hyperesthesia: Increased sensitivity to light (photophobia), sound (phonophobia), and touch.
3. CNS involvement: Agitation or, conversely, depressed consciousness, seizures, vomiting without relief. In meningococcal infection, a characteristic hemorrhagic, star-shaped rash may appear.

Bacterial meningitis requires immediate administration of high-dose intravenous antibiotics. The prognosis directly depends on how promptly therapy is initiated.

Differential Diagnosis

Meningitis must be differentiated from conditions with similar symptoms. For instance, subarachnoid hemorrhage is characterized by sudden “thunderclap” headache without fever at onset. Encephalitis should also be ruled out. Its clinical manifestations are dominated by focal neurological symptoms. Severe infections causing meningism are characterized by irritation of the meninges without inflammation or CSF changes.