Comorbidities Associated With Lichen Planopilaris: A Systematic Review and Meta-Analysis

Lichen planopilaris (LPP) is a primary cicatricial alopecia suggested to be associated with various comorbid medical conditions, including autoimmune, endocrine, and metabolic disorders. However, there is conflicting data regarding these associations. This study quantitatively evaluated the prevalence and odds of comorbidities among patients with LPP. PubMed/MEDLINE, EMBASE, Cochrane Library, and Web of Science were searched from inception to December 25, 2023, to include observational studies reporting prevalent/incident cases of at least one comorbidity in LPP patients. The study adhered to the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA). Risk-of-bias assessment was performed using the Newcastle-Ottawa scale. Random-effect models were utilized to analyze available data. Of the 2535 studies screened, 59 studies were included for meta-analysis, comprising 15,178 LPP patients and 64,735,181 non-LPP controls. Among LPP patients, comorbidities with the highest risk (odds ratio, OR [95% confidence interval, Cl]; prevalence) compared with non-LPP controls and data available from more than one study included lichen planus (15.78 [1.79-139.30]; 6.5%), psoriasis (3.55 [1.10-11.51]; 4.3%), rosacea (3.15 [2.25-4.40]; 10.4%), melanoma (3.11 [1.41-6.87]; 2.3%), systemic lupus erythematosus (3.06 [2.29-4.09]; 1.8%), cutaneous squamous cell carcinoma (3.04 [1.64-5.66]; 4.8%), vitiligo (2.89 [1.60-5.24]; 2.0%), coronary artery disease (1.66 [1.46-1.88]; 7.6%), rheumatoid arthritis (1.50 [1.22-1.84]; 3.5%), hypothyroidism (1.48 [1.12-1.96]; 17.8%), thyroiditis (1.26 [1.08-1.48]; 3.9%), and iron deficiency anemia (1.18 [1.05-1.33]; 9.1%). LPP is significantly associated with autoimmune disorders, thyroid diseases, and skin cancer. Further investigation is required to elucidate the underlying pathogenesis and establish appropriate screening criteria.