# APBA Kısa Özet

This systematic review and meta-analysis pooled data from 21 epidemiological studies representing 38,656,516 individuals to estimate the global prevalence of frontotemporal dementia (FTD). The pooled prevalence was 30 cases per 100,000 population (0.03%; 95% CI, 0.01% to 0.12%). The estimate was accompanied by extreme between-study heterogeneity (I² = 100%), and subgroup analysis showed an association with age range (P = 0.01) but not with geographic region (P = 0.38) or diagnostic criteria era (P = 0.28). These findings provide a reference point, but the wide variability across studies means the result should be interpreted with caution.

# Çalışma neyi araştırdı?

FTD is a leading cause of early-onset dementia in people under 65, yet a comprehensive global prevalence estimate has been lacking. This systematic review and meta-analysis was designed to synthesize available epidemiological data and estimate the worldwide prevalence of FTD. The authors searched multiple databases up to October 31, 2025, selected population-based studies that reported usable prevalence data, and pooled them using meta-analytic methods. In addition to producing an overall estimate, the study examined whether FTD prevalence differed by geographic region, age range, and the era of diagnostic criteria used. The review also assessed potential small-study effects through funnel plot inspection and Egger's test. The study therefore aimed not only to quantify prevalence but also to identify sources of variability in existing estimates.

# Yöntem

The authors conducted a systematic search of multiple literature databases for epidemiological studies on FTD prevalence published up to October 31, 2025. Studies were eligible if they provided prevalence data for FTD. A random-effects model was used for the meta-analysis to account for anticipated variability across study populations and methods. Predefined subgroup analyses compared estimates by geographic region, age range, and diagnostic criteria era. Between-study heterogeneity was quantified using I² statistics. Publication or small-study bias was evaluated by visually inspecting funnel plot symmetry and by performing Egger's test. In total, 21 studies with 38,656,516 individuals met the inclusion criteria and were included in the quantitative analysis. The authors also noted gaps in the available literature, particularly a shortage of high-quality population-based data from regions such as China.

# Temel bulgular

The pooled global prevalence of FTD was estimated at 30 cases per 100,000 people (0.03%, 95% CI: 0.01% to 0.12%). Extreme heterogeneity was present across the included studies (I² = 100%), indicating that variation in prevalence estimates was far beyond what would be expected by chance. In subgroup analyses, prevalence differed significantly by age range (P = 0.01), but not by geographic region (P = 0.38) or by the era of diagnostic criteria (P = 0.28). This suggests that age structure is a meaningful source of variation, while broad regional grouping and diagnostic era did not explain the observed differences. Visual inspection of the funnel plot suggested asymmetry, but Egger's test revealed no statistically significant small-study effects (P = 0.254). The wide confidence interval around the pooled estimate reinforces the marked heterogeneity and imprecision of the overall result.

# Bulgular ne anlama geliyor?

This synthesis provides a useful numerical anchor for FTD prevalence: roughly 30 cases per 100,000 people. However, because heterogeneity was extreme, this estimate should not be treated as a uniform global rate. The significant association with age range supports the understanding that FTD prevalence is not evenly distributed across the lifespan; it may be especially relevant to middle-aged and younger-onset dementia populations. The absence of a significant regional difference is not proof that regional variation does not exist; rather, it may reflect the limited number of studies in some regions and inconsistencies in methodology and case ascertainment. Similarly, the lack of a diagnostic-criteria-era effect does not mean diagnostic changes are irrelevant, but rather that broad historical period grouping may not capture shifts in classification. The review highlights a fundamental gap: existing studies are too heterogeneous and geographically incomplete to support definitive public health conclusions.

# Klinik önem

For clinicians, a pooled prevalence of 30 per 100,000 gives a sense of the scale of FTD, but the more actionable finding is that prevalence varies with age. FTD should remain a consideration in younger patients presenting with behavioral change, language impairment, or executive dysfunction, particularly when the picture does not fit typical amnestic Alzheimer's disease. The wide variability across studies also warns against over-relying on pooled average figures when estimating FTD burden in a particular catchment area or clinical population. Clinicians and health planners should view these results as hypothesis-generating: they support the importance of FTD awareness but not precise local prevalence calculations. The finding that no regional difference was detected may be more a function of data availability than true epidemiological uniformity, and local estimates should be used when available.

# Sınırlılıklar

The interpretation of this meta-analysis is constrained by several limitations. First, the extremely high heterogeneity (I² = 100%) indicates substantial inconsistency in prevalence estimates among the included studies, making the pooled estimate difficult to interpret as a single stable number. Second, prevalence estimates varied widely across studies, further limiting comparability. Third, although funnel plot asymmetry was visually suggested, Egger's test was not significant (P = 0.254), leaving the question of small-study effects unresolved. Fourth, the evidence base is geographically skewed; the authors emphasize the need for more high-quality population-based studies, particularly in underrepresented regions such as China. Fifth, the analysis grouped studies by diagnostic criteria era, but heterogeneity within eras may remain. Finally, the wide confidence interval demonstrates imprecision, and firm prevalence claims cannot be drawn from these data alone. Future work should use standardized case definitions, consistent age stratification, and broader geographic sampling.