Comorbidity Burden in Frontal Fibrosing Alopecia and Lichen Planopilaris: A Systematic Review and Prevalence Meta-Analysis.

Background/Objectives: Frontal fibrosing alopecia (FFA) and lichen planopilaris (LPP) are primary lymphocytic cicatricial alopecias with frequently reported systemic and dermatological comorbidities, although their prevalence and consistency across studies remain uncertain. Methods: We conducted a systematic review and random-effects prevalence meta-analysis following PRISMA 2020 and Joanna Briggs Institute guidance, prospectively registered in PROSPERO (CRD420250656067). MEDLINE, Embase, ClinicalTrials.gov, preprint sources, and reference lists were searched from inception to 18 June 2025 for observational studies reporting comorbidity prevalence in FFA and/or LPP. Results: Sixty studies comprising 4499 patients with FFA and 1370 with LPP were included. In FFA, the highest pooled prevalences among commonly reported conditions included androgenetic alopecia (31.9%), hypertension (23.6%), thyroid disorders (22.2%), hypothyroidism (20.6%), lichen planus pigmentosus (19.6%), and dyslipidemia (17.9%). In LPP, androgenetic alopecia (27.2%), hypertension (21.2%), hypothyroidism (18.7%), vitamin D deficiency (18.3%), dyslipidemia (16.0%), and thyroid disorders (14.5%) were prominent. Several estimates showed substantial between-study heterogeneity. Exploratory subgroup analyses identified study-level sources of heterogeneity for selected outcomes, whereas no meta-regression association remained significant after false-discovery-rate correction. Conclusions: These findings provide a quantitative map of comorbidity burden in FFA and LPP and support targeted, individualized clinical assessment. Because this analysis estimates prevalence within affected populations rather than comparative risk against controls, the findings should not be interpreted as evidence of excess risk or causal relationships.