Sleep disorder associated with antibodies to IgLON5: parasomnia or agrypnia?-Authors' reply.

We read with great interest the paper by Lidia Sabater and colleagues, who describe a novel neuroimmuno logical disease that is a complex, severe sleep disorder associated with antibodies to IgLON5. We have noted a clinically similar disorder in a single patient who had serum and CSF antibodies to the metabotropic GABAB receptor. Similar to the patients in Sabater and colleagues’ report, our patient developed a complex neurological syndrome at age 55 years that was characterised by diplopia, slight fl uctuating bilateral palpebral ptosis, and, later, dysphagia, dysphonia, tongue weakness, stridor, severe dysautonomia, and central hypoventilation, which required assisted ventilation during sleep. The outcome was also similar to the outcomes reported by Sabater and colleagues. Despite long periods of amelioration after plasma exchange and immunosuppressive treatment, the patient died suddenly during sleep 10 years after the onset of the disease. Sleep recordings showed a period of complete sleep loss in the acute phases of the disease. Agrypnia has been associated with neuroimmunological disorders, and particularly with Morvan’s chorea. Essentially, it is a complete loss of sleep, with the elimination of slowwave sleep and sleep spindles that are associated with sustained motor and autonomic activation. We believe that this peculiar sleep disorder described by Sabater and colleagues has several features in common with the syndrome described by Lugaresi and colleagues as agrypnia excitata: the presence of undiff erentiated nonrapid-eye movement sleep stages; the absence of the rapid-eye-movement atonia; the dysautonomia disorder; and the continuous motor activity during sleep. The fi nalistic movements described in Sabater and colleagues’ paper might be interpreted as episodes of oneiric stupor, which is probably an exclusive sign of agrypnia excitata and it is the recurrence of stereotyped gestures mimicking simple daily life activities. However, the patients had some episodes of N3 stage sleep, preserved K complexes slow-wave sleep, and spindles, which are not the typical fi ndings in agrypnia excitata. Nevertheless, in all disorders associated with agrypnia excitata, spindles, K complexes, and slow-wave sleep show a progressive reduction before disappearing. In our patient and other cases of agrypnia in our clinical experience, the sleep pattern and the other neurological symptoms had a relapsing-remitting course. In sleep recordings done serially and prolonged for several consecutive days, slow-wave sleep and spindles presented alternated periods of total suppression with periods of partial reduction, associated with the clinical fl uctuation. Therefore, we suggest that the disorder elegantly described by Sabater and colleagues, which was associated with anti-IgLON5 autoantibodies, could be regarded as a type of agrypnia excitata rather than as a parasomnia, similar to that seen in other neuroimmunological diseases.