Phenotypes and epidemiology of frontotemporal dementia in Iceland

Background: Frontotemporal dementia (FTD) is a group of neurodegenerative disorders, with three distinctive phenotypes each presenting with different symptoms. The pathology of FTD is characterized by degeneration of the frontal and temporal lobes of the brain. The aim of this project was to investigate the prevalence and incidence of FTD in Iceland over the last few decades and gather information about demographics, clinical symptoms and diagnostic methods as well as to compare the three phenotypes with respect to clinical symptoms. Patients with FTD typically receive their diagnosis at Landspitali memory clinic in Reykjavik. Methods: The study population consisted of individuals who had been diagnosed with frontotemporal dementia from the beginning of electronic medical records at Landspítali until 2022. Medical records were used for data collection and descriptive and analytical statistical methods were used for data processing and analyses. Results: The frequency of FTD in Landspitali memory clinic population from the years 2008-2022 was found to be 1,7%. Over the entire period, a total of 97 individuals received the diagnosis, 50 men and 47 women. The prevalence was 45.3/100,000 inhabitants and the average incidence was 11.67/100,000/year. Mean age at onset of symptoms was 67 years. The behavioral variant of FTD was the most common phenotype, and the most common clinical feature of all three phenotypes was memory impairment. Discussion: The prevalence of frontotemporal dementia in Iceland is lower than has been reported in some previous studies, incidence comparison is difficult due to difference in age distribution in different studies. Prevalence in the memory clinic population was low, reflecting the rarity of FTD. The average age at diagnosis was higher in Iceland than described in foreign studies and the frequency of memory impairment as an initial symptom was higher compared to foreign studies. Diagnostic methods have developed in recent years and the diagnostic process is more precise than in the earlier years of the study period.