Anti-IgLON5 disease has recently been characterized. Core manifestations include sleep disturbances, bulbar dysfunction, gait instability, chorea and cognitive decline, while seizures are not typical. Response to immunotherapy is usually suboptimal and prognosis is frequently poor, although early treatment could improve outcomes.

A 49-year-old woman had an 18-year-history of temporal lobe epilepsy that developed after cervical cancer. Brain MRI was unremarkable but EEG showed right temporal epileptiform discharges and PET showed right temporal hypometabolism, compatible with right temporal seizure origin. Due to seizure refractoriness and history of cancer, comprehensive neural antibody testing for possible autoimmune-associated epilepsy was pursued and revealed anti-IgLON5 in serum and cerebrospinal fluid. On directed history, the patient reported snoring and insomnia that had developed two years prior, which were symptoms she had not initially volunteered because she felt they were mild and stable. Neurologic examination was unremarkable. The patient received a six-week trial of corticosteroids, without improvement in seizure frequency or sleep disturbances. Polysomnography revealed minimal sleep disordered breathing, mild arousals from slow wave sleep, unusually prominent beta activity in REM sleep, and excessive fragmentary myoclonus, which may represent early anti-IgLON5 disease.

Diagnostically, we hypothesize that anti-IgLON5 is unrelated to chronic temporal lobe epilepsy in our patient, which we suspect is idiopathic. However, this antibody may explain sleep findings, and the mildness of her symptoms referable to anti-IgLON5 disease creates a unique therapeutic dilemma. In discussion with the patient, we have opted to monitor clinically and with polysomnography, and to consider institution of further immunotherapy if there is demonstrable disease progression. Future study into the natural history of anti-IgLON5 disease is needed to determine the optimal management of patients with mild symptoms.