Cutaneous lichen planus beyond the skin: tricho-onychoscopic and systemic insights

Cutaneous lichen planus (CLP) often involves the scalp and nails subclinically. Early appendageal signs are underrecognized despite their potential for timely diagnosis and prevention of irreversible damage. To determine the frequency of mucosal and appendageal involvement in CLP, assess potential contributing factors (e.g., medications, systemic diseases, vaccines), and identify early trichoscopic and onychoscopic features. A retrospective study was conducted on 108 patients with histopathologically confirmed CLP. Data included clinical, trichoscopic, onychoscopic, and systemic parameters. Drug histories were classified using the WHO ATC system. Scalp involvement was detected in 29.6% of patients, including 19.4% with non-scarring subclinical inflammation detectable only by trichoscopy. Perifollicular whitish-grey scaling, follicular plugging, yellow areas, and milky-red areas were significantly associated with scarring alopecia (p<0.001). Nail involvement was found in 43.5%, with red nail bed (24.1%) and longitudinal ridging (23.1%) being most frequent. Longitudinal onychoschizia, a newly proposed onychoscopic sign, was noted in 9.3% of patients. Nail and scalp involvement were positively correlated (r=0.289, p=0.002). Common potential triggers included antihypertensives, oral antidiabetics, NSAIDs, levothyroxine, and dental restorations. Autoimmune diseases were present in 15.7%, with Hashimoto's thyroiditis being the most common (10.1%). Appendageal involvement in CLP may be more prevalent and underdiagnosed than previously recognized. Trichoscopy and onychoscopy are valuable for detecting early inflammatory changes, including novel signs such as longitudinal onychoschizia. Routine dermoscopic evaluation of the scalp and nails should be considered in all CLP patients, regardless of visible appendageal findings.