6th August 2024

Special considerations

Some patients presenting with a clinical picture of meningitis and/or encephalitis may have features in the history requiring further assessment, as well as follow on actions that may need to be considered:

• Immunosuppression: those with HIV and other immunodeficiencies are at risk of opportunistic infections with atypical organisms and if they present with features of meningitis and/or encephalitis, should be assessed for these. Cryptococcus neoformans is an invasive fungus for which having a CD4 count of <100 is a risk factor, and may present initially with pulmonary disease with progression to the CNS. Classically, Indian ink staining has been used to detect it in the CSF, but cryptococcal antigen is more sensitive. If suspected, it should be empirically treated until ruled out. Patients with a relative immunodeficiency, for example as a result of age or diabetes, are more at risk of less common organisms, including Listeria, for which cover with ampicillin is required.
• Travel history: patients with recent travel or migration who present with altered consciousness levels and/or seizures should be evaluated for potential imported or rare pathologies. TB meningitis can occur even in the absence of active pulmonary TB and should be considered in patients from a high prevalence area with suggestive symptoms and signs. Those who have travelled to areas with mosquitos must have malaria considered and have blood smears carried out for this. More temperate areas with mosquitos, especially in the US, may have a higher incidence of West Nile virus. Potential tick exposure should prompt consideration of tick-borne encephalitis or Lyme disease. If there is a history of travel to areas with an increased prevalence of penicillin-resistant pneumococci, then rifampicin should be added to the initial treatment regimen.
• Malignancy: some solid malignancies, namely melanoma, non-small cell lung cancer, and breast cancer, as well as haematological malignancies including lymphomas, can spread to the leptomeninges, causing a range of symptoms. This is usually as a result of haematogenous spread but may also be direct invasion or (rarely) a primary tumour. Patients may complain of headache, nausea, or lower limb weakness, but signs may be subtle, including cerebellar dysfunction and meningeal irritation. There may also be signs and symptoms of an obstructive hydrocephalus. Investigation is via cytology for malignant cells in the CSF, which may also have a raised protein.
• Other epidemiological factors: unusual causes can be associated with exposure to carriers of pathogens, human or animal, in those susceptible to severe disease. For example, cat scratch disease, caused by Bartonella henselae, can cause encephalitis in a small minority of cases. Those unvaccinated against measles, mumps and rubella (MMR) may be at risk of encephalitis from these causes if exposed.
• Contacts of confirmed meningococcal disease: meningitis and encephalitis are notifiable diseases in the UK. Those who are contacts of patients with confirmed N. meningitidis meningitis should be offered prophylaxis: single dose ciprofloxacin or rifampicin for 2 days as second line. For non-B serotypes, an ACWY vaccine should be offered.