SummaryThe clinical features of viral encephalitis consist of headache, fever, seizures and encephalopathy. We report three patients with high-grade gliomas presenting with encephalitic illnesses. The diagnosis of brain tumour should always be borne in mind if definite evidence for a viral infection is not obtained.Keywords: glioma; viral encephalitis; encephalopathy Viral encephalitis is characterised by headache, confusion, altered consciousness with or without seizures, and fever. The most commonly identified cause of sporadic communityacquired encephalitis is herpes simplex virus (HSV) type I, which may be diagnosed on viral culture of cerebrospinal fluid (CSF), polymerase chain reaction (PCR) analysis looking for HSV DNA, serological testing for IgM antibodies, or brain biopsy. Characteristically the virus attacks the medial temporal lobes and insular cortex giving rise to a focal encephalitis which carries a significant mortality rate. 1 Rarely, the patient presents with symptoms and signs of raised intracranial pressure, giving rise to the possibility of a temporal lobe abscess. The converse situation, whereby a high-grade tumour presents as an acute encephalitic illness, has only rarely been reported. The following three cases illustrate that this diagnosis should always be borne in mind if definite evidence for a viral infection causing the encephalopathy is not obtained, especially if the PCR test is negative for the presence of viral DNA. Case reportsCase 1 A 41-year-old woman presented with tonicclonic seizures, fever, drowsiness and confusion. Magnetic resonance imaging (MRI) showed extensive high signal abnormality in the left temporal lobe and posterior parietal region (figure 1). CSF was normal. A presumptive diagnosis of herpes simplex encephalitis (HSE) was made and she improved after intravenous acyclovir. However, her seizures persisted and 2 years later her MRI scan showed an increase in the size of the temporal lesion (figure 1). Approximately one month later, she was found unconscious at home. A CT scan now showed a large lesion with considerable midline shift. Emergency decompression was unsuccessful and she died without regaining consciousness. The histology of the lesion was glioblastoma multiforme. Case 2A 49-year-old man became acutely confused and then had serial tonic-clonic seizures. On admission he was pyrexial, tachycardic and unconscious. MRI showed extensive high T2 signal change aVecting the right temporal and frontal lobes with some mass eVect (figure 2). CSF examination including PCR for HSV DNA was negative. He was started on acyclovir and gradually improved. He had persistent simple partial seizures and a repeat MRI 3 weeks later showed no change. A stereotactic brain biopsy was carried out and revealed an anaplastic astrocytoma. He was treated with external beam radiotherapy followed by combination chemotherapy. Case 3A 72-year-old woman presented with a 2-week history of episodes of vagueness and confusion. MRI revealed a lesion involving the grey and white matter of the...

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