NeurologyTier 2Disease (DEADMAN)

Limbic encephalitis

Description

Inflammation of the medial temporal lobes/limbic system, causing subacute memory impairment, seizures, and psychiatric change - autoimmune (antibody-mediated) or paraneoplastic in most identified cases

Peak incidence varies by antibody - anti-LGI1 typically older patients (median 60s), less often paraneoplastic; anti-NMDAR typically younger patients/women, more often with an ovarian teratoma

Antibodies against neuronal cell-surface/synaptic proteins (not intracellular, unlike classic paraneoplastic antibodies) are directly pathogenic and generally more treatment-responsive
VGKC-complex antibody testing is now obsolete - replaced by specific testing for anti-LGI1 and anti-CASPR2, which better predict phenotype and paraneoplastic risk
Anti-NMDAR encephalitis - often ovarian teratoma-associated in young women; classic evolution from psychiatric symptoms -> seizures -> movement disorder/autonomic instability -> decreased consciousness

MRI brain - T2/FLAIR hyperintensity in one or both medial temporal lobes (may be normal, especially early or in anti-NMDAR encephalitis)
CSF - lymphocytic pleocytosis, oligoclonal bands; serum AND CSF antibody testing (CSF more sensitive for anti-NMDAR)
EEG - often abnormal (temporal slowing, epileptiform discharges; "extreme delta brush" described in anti-NMDAR)
Tumour screen mandatory once an antibody is identified - CT chest/abdomen/pelvis +/- pelvic ultrasound/MRI (ovarian teratoma), testicular ultrasound, PET if the initial screen is negative

First-line: high-dose corticosteroids + IVIG or plasma exchange
Second-line (refractory): rituximab and/or cyclophosphamide
Tumour removal (e.g. teratoma resection in anti-NMDAR encephalitis) is central to treatment when a tumour is found and often produces marked improvement
Seizures managed with standard antiepileptics alongside immunotherapy

Ovarian teratoma (anti-NMDAR), thymoma (anti-CASPR2), small cell lung cancer (classic paraneoplastic antibodies - anti-Hu, anti-Ma2), faciobrachial dystonic seizures (near-pathognomonic for anti-LGI1)

Cell-surface antibody-mediated encephalitis (LGI1, NMDAR, CASPR2) generally responds well to immunotherapy, unlike classic paraneoplastic (intracellular antigen) encephalitis, which responds poorly regardless of tumour treatment
Relapse can occur, particularly in anti-NMDAR encephalitis without tumour resection

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