The diagnosis of<unk>  is extremely difficult and it is usual for the diagnosis to be delayed for weeks. The key diagnostic test (detection of specific auto-antibodies in cerebrospinal fluid) is not routinely offered by most immunology laboratories. Some of the rarer auto-antibodies (e.g., NMDAR) have no commercially available assay and can only be measured by a very small number of research laboratories worldwide, further delaying diagnosis by weeks or months. Most patients with<unk>  are initially diagnosed with herpes simplex encephalitis, because the two syndromes cannot be distinguished clinically. HHV-6 (human herpes virus 6) encephalitis is also clinically indistinguishable from<unk> . There are two sets of diagnostic criteria used. The oldest are those proposed by Gultekin et al. in 2000. Gultekin criteria EITHER, Pathological demonstration of<unk>  OR, All four of: * Short-term memory loss, seizures, or psychiatric symptoms suggestive of<unk>  system involvement * <4 years between onset of neurological symptoms and cancer diagnosis * Exclusion of metastases, infection, metabolic and nutritional deficits, stroke and side-effects of therapy that may cause<unk>  encephalopathy * At<unk> ast one of * CSF with inflammatory findings * Hyperintensity of the temporal lobes bilaterally on MRI FLAIR or T2 * EEG with epilepsy or slow activity involving the temporal lobes focally A revised set of criteria were proposed by Graus and Saiz in 2005. Graus and Saiz criteria All four of * Subacute onset (<12 weeks) of seizures, short-term memory loss, confusion, and psychiatric symptoms * Neuropathologic or radiologic evidence (MRI, SPECT, PET) of involvement of the<unk>  system * Exclusion of other possible aetiologies of<unk>  dysfunction * Demonstration of a cancer within 5 years of the diagnosis of neurologic symptoms, or the development of classic symptoms of<unk>  dysfunction in association with a well-characterized paraneoplastic antibody (Hu, Ma2, CV2, amphiphysin, Ri) The main distinction between the two sets of criteria is whether or not the detection of a paraneoplastic antibody is needed for diagnosis. Antibodies against intracellular neuronal antigens The main antibodies within this group are those against Hu, Ma2, CV2, amphiphysin and Ri. The syndrome of anti-Ma2 encephalitis may be clinically mistaken for Whipple's disease. Antibodies against cell membrane antigens The main antibodies within this group are those against N-methyl-D-aspartate receptors (NMDAR) and the voltage-gated potassium channel-complex (VGKC-complex). Anti-NMDAR encephalitis is strongly associated with benign tumours of the ovary (usually teratomata or dermoid cysts). Anti-VGKC-complex encephalitis is most often not associated with tumours. Patients with NMDAR encephalitis are frequently young women who present with fever, headache and fatigue. This is often misdiagnosed as influenza, but progresses to severe behavioural and personality disturbance, delusions, paranoia and hallucinations. Patients may therefore initially be admitted to a psychiatric ward for acute psychosis or schizophrenia. The disease then progresses to catatonia, seizures and loss of consciousness. The next stage is hypoventilation (inadequate breathing) requiring intubation, orofacial dyskinesia and autonomic instability (dramatic fluctuations in blood pressure, temperature and heart rate). Investigation Cerebrospinal fluid (CSF) Examination of cerebrospinal fluid (CSF) shows elevated numbers of lymphocytes (but usually < 100 cells/μl); elevated CSF protein (but usually <1.5 g/l), normal glucose, elevated IgG index and oligoclonal bands. Patients with antibodies to voltage-gated potassium channels may have a completely normal CSF examination. Neuroimaging Brain MRI is the mainstay of initial investigation pointing to<unk>  lobe pathology revealing increased T2 signal involving one or both temporal lobes in most cases. Serial MRI in<unk>  starts as an acute disease with uni- or bilateral swollen temporomesial structures that are hyperintense on fluid attenuation inversion recovery and T2-weighted sequences. Swelling and hyperintensity may persist over months to years, but in most cases progressive temporomesial atrophy develops. PET-CT is not an essential investigation but can help in suspected cases with MRI negative for early diagnosis. Neuro-electrophysiology EEG is mostly nonspecific slowing and epileptiform activity arising from temporal lobes.
Limbic encephalitis
La Crosse encephalitis
Powassan encephalitis
Saint Louis encephalitis
Autoimmune encephalitis
Rasmussen's encephalitis
Japanese encephalitis
Viliuisk encephalomyelitis