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Lotte Sahin Levison,1 Reimar Wernich Thomsen,2 Diana Hedevang Christensen,2 Thomas Mellemkjær,1 Søren Hein Sindrup,3 Henning Andersen11Department of Neurology, Aarhus University Hospital, Aarhus, Denmark; 2Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark; 3Department of Neurology, Odense University Hospital, Odense, DenmarkPurpose: To validate the diagnostic codes for Guillain-Barré syndrome (GBS) in the Danish National Patient Registry (DNPR). Secondly, to examine 30-year trends in the incidence of GBS in Denmark.Patients and methods: We used the DNPR to identify all patients aged 16 and above diagnosed with a primary GBS diagnosis at any Danish department of neurology between 1987 and 2016. Medical files were reviewed according to the clinical criteria of the National Institute of Neurological Disorders and Stroke Committee and classified according to the Brighton criteria. The incidence rate (IR) was calculated based on data from 1987 to 2016 and stratified by season, gender, and age.Results: Over 30 years, we identified 2,319 patients aged 16 and above in the DNPR. From a validation cohort of 573 patients, we were able to retrieve 425 (74.2%) medical files; 356 GBS diagnoses were confirmed. The overall positive predictive value was 83.8% (95% confidence interval (CI): 80.0–87.0). In 99% of the confirmed patients, the Brighton criteria level 1–3 for GBS were met. The IR was fairly stable over 30 years at 1.77 per 100,000 person years (95% CI: 1.70–1.84). The incidence was higher in the winter season (IR ratio compared with summer: 1.18 (95% CI: 1.09–1.29)), and was strongly associated with male gender (IR ratio vs females: 1.44 (95% CI: 1.33–1.57)). IRs rose with age at diagnosis, particularly after the age of 50 in both men and women and a minor peak was observed for total IR in young adults.Conclusion: Primary diagnostic codes for GBS at Danish departments of neurology have high validity. The DNPR is a well-suited data source for epidemiological research on GBS. The Danish nationwide 30-year GBS IR is stable over time and similar to GBS IRs reported in other European and North American populations.Keywords: registries, positive predictive value, international classification of disease codes, epidemiology

As the neurointervention field grows, a new side effect emerges. Delayed leukoencephalopathy (DL) is believed to be an inflammatory or allergic reaction to polymer material that is shed from catheters during endovascular procedures. We present four cases of DL after aneurysm treatment in two patients, endovascular stroke treatment and diagnostic arteriography. We present our diagnostic process, including biopsy results in two patients, our anti-inflammatory treatment and outcomes together with a review of the literature. In our series, prognosis was variable with ongoing seizures in two patients. Our literature review reveals that asymptomatic shedding of polymer material is common, occurring in a third of endovascular stroke procedures, whereas symptomatic DL occurs in <0.5% of therapeutic neuroendovascular procedures. Clinicians should be aware of this rare complication, and oral glucocorticoids seem to be a reasonable first-line treatment strategy.