Table 2.

Additional diagnosis and investigations to consider in specific groups of patients. ∗All investigations in this section should be performed irrespective of the cause of immunosuppression. ^†Investigations for returning traveller and autoimmune encephalitis are specific to the condition under consideration. Acute disseminated encephalomyelitis (ADEM), John Cunningham virus (JC), Myelin oligodendrocyte glycoprotein (MOG), White cell count (WCC).

Group	Disorder	Investigations to consider
All patients		CSF opening pressure CSF WCC and differential CSF protein Paired CSF and serum glucose CSF Gram stain Blood and CSF cultures CSF PCR for meningococcus, pneumococcus, HSV 1 and 2, VZV and enterovirus
Immunocompromised patients∗	HIV After transplant Haematological malignancy Immunosuppressant therapy	CMV and EBV PCR HHV 6/7 PCR JC virus PCR HIV serology Toxoplasma serology with or without PCR Cryptococcal antigen/India ink stain Aspergillus PCR Galactomannan CSF M. tuberculosis culture and acid-fast bacilli PCR
Returning traveller†	Cerebral malaria Flaviviridae Japanese encephalitis Dengue encephalitis St Louis encephalitis West Nile encephalitis Tick-borne encephalitis Togaviridae Eastern encephalitis Western encephalitis Venezuelan encephalitis Reoviridae Colorado tick fever Rhabdoviridae Rabies encephalitis Chandipura virus Henipaviridae Nipah virus	Rapid blood antigen test Thick and thin blood films CSF PCR/serology CSF PCR/serology CSF PCR/serology CSF PCR/serology CSF PCR/serology CSF serology CSF serology CSF serology CSF PCR/serology CSF PCR/serology CSF serology CSF PCR/serology
Autoimmune encephalitis†	Anti-NMDA receptor encephalitis Anti-VGKC complex encephalitis Bickerstaff's encephalitis Paraneoplastic encephalitis Hashimoto's encephalitis ADEM	Anti-NMDA receptor antibodies Anti-VGKC complex antibodies Anti-GQ1b antibodies ANNA 1/Anti-Hu ANNA 2/Anti-Ri Anti-Ma1/Anti-Ma 2 Anti-amphiphysin Anti-thyroid peroxidase antibodies MOG antibodies