Synopsis
Recognise subacute immune-mediated encephalopathy among psychiatric, epileptic and infectious mimics, obtain paired diagnostic samples and coordinate early neurological, tumour and critical-care treatment.
- Autoimmune encephalitis typically evolves over days to fewer than three months with impaired memory, altered mental state or psychiatric change plus seizures, focal findings, CSF inflammation, EEG abnormalities or compatible MRI features.
- A first psychotic presentation with catatonia, seizures, dyskinesia, fluctuating consciousness or autonomic disturbance needs an organic assessment; age alone must not divert the patient exclusively into a psychiatric pathway.
- Anti-NMDA-receptor encephalitis often progresses from psychiatric and cognitive symptoms to seizures, oro-facial dyskinesia, autonomic instability and hypoventilation, especially in younger people.
- LGI1 encephalitis is suggested by very brief frequent faciobrachial dystonic seizures, memory loss, temporal-lobe seizures and hyponatraemia, often before routine MRI or CSF becomes striking.
- Send both CSF and serum neuronal-antibody panels through an accredited laboratory because sensitivity and specificity differ by antibody; a serum-only low-positive result can mislead.
- Do not wait for an antibody result to give intravenous aciclovir when herpes simplex encephalitis remains possible, or to treat a compelling severe autoimmune syndrome after appropriate samples and specialist review.
- MRI may be normal, particularly in NMDAR disease; EEG can reveal non-convulsive seizures or characteristic slowing but is rarely antibody-specific.
- Search for a phenotype-linked tumour, such as ovarian teratoma with NMDAR antibodies or small-cell lung cancer with certain intracellular antibodies, and repeat screening when specialist guidance indicates.
- First-line immunotherapy usually combines high-dose corticosteroid with intravenous immunoglobulin or plasma exchange; rituximab or cyclophosphamide is considered when response is inadequate.
- Recovery is often slow and uneven, requiring neurorehabilitation, neuropsychology, speech and language therapy, epilepsy review and support for families long after inflammation is controlled.
Key red flags
A younger patient develops anxiety, insomnia, psychosis or cognitive change, then seizures, catatonia, oro-lingual or limb dyskinesia, autonomic swings and central hypoventilation. An ovarian teratoma is an important association.
An older adult has dozens of brief unilateral face-and-arm dystonic episodes, new memory impairment and hyponatraemia. These seizures may precede full limbic encephalitis and warrant urgent specialist recognition.
Subacute anterograde amnesia, confusion, mood or behavioural change and focal temporal seizures accompany mesial-temporal MRI signal or EEG abnormalities. HSV and tumour-associated causes remain key alternatives.
Status epilepticus, reduced consciousness, temperature or blood-pressure instability, arrhythmia, hypersalivation and hypoventilation indicate severe network and autonomic involvement requiring intensive monitoring.
Investigation priorities
Identify limbic or extra-limbic inflammation and exclude stroke, tumour, abscess, demyelination and other structural causes.
Management branches
Encephalopathy is accompanied by seizure, autonomic instability, hypoventilation or falling consciousness.
- Use ABCDE, check bedside glucose, protect the airway, treat status epilepticus through the emergency protocol and obtain critical-care input for hypoventilation, dysrhythmia or severe autonomic fluctuation.
- After blood cultures and prompt lumbar puncture when safe, start intravenous aciclovir at the locally adjusted encephalitis dose while HSV remains plausible; add antibacterial therapy if meningitis cannot be excluded.
- Arrange urgent MRI and EEG, send paired serum and CSF antibodies, and involve neurology before sedating behavioural symptoms in ways that could conceal seizures or worsen autonomic instability.
- Use careful low-stimulus nursing, venous-thromboembolism prevention, nutrition, bladder, bowel, pressure and family-support plans during prolonged reduced consciousness.