Abstract
INTRODUCTION: Subungual squamous cell carcinoma is a rare malignancy of the nail unit that is frequently misdiagnosed as benign nail disease, leading to prolonged diagnostic delays and sometimes invasive spread. OBJECTIVE: To synthesize the dermoscopic features of histologically confirmed subungual squamous cell carcinoma and to compare patterns between invasive and in situ disease. METHODS: We performed a systematic review and meta-analysis (PROSPERO CRD42023470387) following PRISMA and MOOSE guidance. PubMed, Scopus and Cochrane CENTRAL were searched. Extracted data included study design, lesion counts, histologic subtype and specific dermoscopic signs. Random-effects meta-analysis (DerSimonian-Laird with Freeman-Tukey transformation) produced pooled prevalences with 95% confidence intervals. Between-study heterogeneity was assessed with Cochran's Q and I(2). We used subgroup and meta-regression analyses to explore the influence of histologic subtype, sample size and publication year. When the data allowed, diagnostic odds ratios were calculated versus common benign mimickers. RESULTS: Twenty studies comprising 121 lesions (96 invasive, 25 in situ) were included. In invasive lesions, the most common dermoscopic findings were subungual hyperkeratosis (pooled prevalence 89%; 95% CI 78-97; I(2) = 0%), onycholysis (85%; 75-93; I(2) = 28%), irregular borders (72%; 50-90; I(2) = 42%), and splinter hemorrhages (52%; 40-65; I(2) = 36%). In situ lesions more often presented with melanonychia (89%) and showed lower rates of hyperkeratosis (50%). Meta-regression identified histologic subtype as a significant predictor of feature prevalence (p < 0.01). Key comparative performance estimates included a diagnostic odds ratio of 12.6 (95% CI 8.3-19.1) for polymorphous vessels distinguishing squamous cell carcinoma from warts and 6.8 (95% CI 3.2-14.5) for hyperkeratosis versus onychomycosis. CONCLUSIONS: Dermoscopy reliably identifies features, particularly hyperkeratosis, onycholysis, irregular margins and hemorrhagic spots, that are common in invasive subungual squamous cell carcinoma; in situ disease more commonly presents with pigmentary changes. Recognition of these signs should lower the threshold for biopsy of suspicious single-digit nail lesions and may facilitate earlier diagnosis and treatment.