Treatable autoimmune encephalitis diagnosed with phenotype-specific evaluation
Clinical cases: Neurology
Background
A 65-year-old man presented with brief, frequent episodes of involuntary movements affecting the right side of his face and right arm. The events lasted only a few seconds but occurred dozens of times per day and were characterized by sudden dystonic posturing of the arm with ipsilateral facial grimacing. Over several weeks, the patient also developed progressive confusion, short-term memory impairment, and behavioral changes.
EEG monitoring captured multiple brief dystonic events involving the right side of the face and right arm without an electrographic ictal correlate. A brain MRI was unremarkable. Laboratory evaluation revealed mild hyponatremia.
A paraneoplastic autoantibody evaluation (Mayo ID: PAVAL) was ordered from an outside hospital and returned a negative result. The patient was suspected to have focal motor seizures and was referred to Mayo Clinic for further evaluation. On neurologic assessment at Mayo Clinic, the patient’s clinical presentation — particularly the presence of faciobrachial dystonic seizures (FBDS), cognitive decline, and hyponatremia — raised concern for LGI1 IgG autoimmune encephalitis. A serum autoimmune encephalopathy panel (Mayo ID: ENS2) was subsequently ordered.
LGI1 IgG cell-based assay (CBA) testing in serum returned a positive result, confirming the diagnosis of LGI1 IgG autoimmune encephalitis. Review of the initial testing revealed that the LGI1 IgG CBA was not included as part of the original PAVAL panel at the time of testing. The patient was treated with high-dose corticosteroids followed by rituximab, resulting in the resolution of seizures and gradual improvement in cognitive function.
Teaching points
- FBDS are highly characteristic of LGI1 IgG autoimmune encephalitis and often precede cognitive decline. These seizures frequently lack an ictal correlate on EEG.
- Hyponatremia can provide an important diagnostic clue in patients with suspected LGI1 encephalitis.
- LGI1 IgG is not classified as a high- or intermediate-risk paraneoplastic antibody and therefore is not included in PAVAL. It is one of the most common antibodies associated with autoimmune encephalitis in adults and is included in ENS2.
- Early recognition and immunotherapy are critical, as prompt treatment can reduce seizure burden and prevent progression to severe limbic encephalitis.
Key testing
ENS2 | Encephalopathy, Autoimmune/Paraneoplastic Evaluation, Serum
- Turnaround time: 12 days
Learn more about our phenotype-specific evaluation for autoimmune encephalitis.
