Clinical features

Symptoms include severe headache, fever, vomiting, photophobia and convulsions leading to drowsiness and unconsciousness. Signs are mainly those of meningeal irritation, i.e. neck and spinal stiffness, and Kernig’s sign (pain and resistance on extending the knee when the thigh is flexed). These cardinal signs and symptoms may be absent in neonatal meningitis and meningitis in the elderly and the immunocompromised. Sequelae include encephalopathy (altered cerebral function), cranial nerve palsies, cerebral abscess, obstructive hydrocephalus and subdural effusion of sterile or infected fluid.

Aetiology

The common types of bacterial meningitis and the major agents are:

Epidemiology, treatment and prevention

N. meningitidis (the meningococcus) is the main agent of meningitis in the UK and USA and most infections are caused by group B strains. The disease is common in children and young adults. Penicillin is the drug of choice: cefotaxime and chloramphenicol are alternatives. Haemophilus meningitis is mostly seen in children between 1 month and 4 years old and is treated with chloramphenicol or cefotaxime. Pneumococcal infection, common in older patients and those without a functioning spleen, is treated with penicillin. Tuberculous infection is managed by ‘triple therapy’, as described in Chapter 23.

Meningitis may spread quickly in close household contacts. Avoiding overcrowding in living and working conditions is helpful. Chemoprophylaxis with antibiotics (e.g. rifampicin) in meningococcal infection can eliminate the carrier state, which may develop in some.

Meningitis due to other organisms

Rarely, other organisms, such as Listeria monocytogenes, Leptospira interrogans and Cryptococcus neoformans (a fungus), may cause meningitis.

Laboratory diagnosis

Examination of the cerebrospinal fluid, usually obtained by a lumbar puncture, is essential. Changes that occur in the cerebrospinal fluid, depending on whether the aetiology is acute pyogenic, tuberculous or viral, dictate appropriate and timely therapy (Table 25.1). Cerebrospinal fluid should also be centrifuged and the deposit Gram-stained and cultured to isolate and identify the causative agent. Blood cultures are also useful in the diagnosis of bacterial meningitis.

Treatment

Treatment is dictated by the causative organism and its antibiotic sensitivity; because of the serious nature of the illness, empirical therapy with two or three antibiotic drugs is given immediately.

Pathogenesis

The major routes of viral entry into the body are the respiratory and gastrointestinal tracts. From these portals, they spread to the central nervous system by direct migration via the olfactory nerves or indirectly via blood. Cells involved in viral spread include capillary endothelial cells, epithelial cells of the choroid plexus and infected leukocytes.

Epidemiology

Children and young adults are the most affected.

Treatment

Viral meningitis is a benign, self-limiting condition and requires only symptomatic treatment. No antiviral drugs are indicated as the condition resolves in 1–2 weeks.