Leucine-rich glioma inactivated 1 (LGI1) antibody encephalitis is a limbic autoimmune encephalitis characterized by cognitive manifestations and behavior changes. The most distinctive symptom of LGI1 encephalitis is faciobrachial dystonic seizures (FBDS), which classically consist of short hemi-facial and ipsilateral upper limb contractions. FBDS often precedes cognitive decline, memory disturbances, and neuropsychiatric symptoms. Early diagnosis and treatment demonstrate better clinical outcomes in patients, however, prompt diagnosis continues to prove difficult. Current diagnostic guidelines include anti-LGI1 laboratory testing, brain imaging, EEGs, and detailed clinical observations. Moreover, presentations in children are more heterogenous making diagnoses more challenging. Our patient uniquely presented with lower extremity dystonic seizures instead of FBDS thus obfuscating a clear diagnosis.

Case Presentation: 

A 17-year-old boy presented with an episode of generalized tonic-clonic seizure. It was preceded by multiple shorter episodes of dystonic posturing of the left lower extremity. The maximum frequency of episodes was 30 per hour. During initial admission, he was treated with Levetiracetam, Topiramate which controlled his symptoms. One week later he had a breakthrough seizure, requiring readmission. He was evaluated with long term EEG, cerebrospinal fluid studies, and serum Autoimmune encephalitis panel.   

EEG captured numerous episodes, which reported no ictal changes, but revealed occasional frontal predominant slowing and intermittent rhythmic delta activity. Although EEG was inconclusive, given the frequency of episodes he was treated with Lacosamide. MRI revealed extra axial fluid collection overlying the anterior cranial fossa and was negative for intracranial lesions, though the patient’s braces limited the picture. Autoimmune encephalitis panel tested positive for LGI1-IgG antibody. He then received IVIG which has helped with his symptoms.

LGI1 encephalitis presents with FBDS, classically involving the face and the upper extremity in adults. Our uniquely presenting pediatric patient with lower extremity dystonic seizures emphasizes the importance of broad diagnostic criteria and maintaining comprehensive differentials.