Early-Onset Leukonychia as a Diagnostic Clue in Familial Hailey-Hailey Disease.

Hailey-Hailey disease (HHD) is a rare autosomal dominant genodermatosis characterized by recurrent intraepidermal blistering and erosions, most often affecting flexural and intertriginous areas. Although its clinical presentation is distinctive, the disease exhibits considerable variability and is often misdiagnosed, particularly in early or atypical forms. Nail involvement, historically considered absent, has recently been recognized as an underappreciated feature that may provide valuable diagnostic clues. We report a familial case of HHD spanning three generations, in which a single longitudinal leukonychia in the proband preceded the onset of typical skin lesions. The initial nail change, unassociated with trauma or systemic disease, prompted a detailed family history revealing recurrent erosive lesions in relatives. Months later, the proband developed painful, fissured, erythematous plaques in flexural regions, confirmed histologically as HHD. Treatment with topical calcineurin inhibitors, oral doxycycline, and ultraviolet B (UVB) phototherapy led to marked clinical improvement and reduced flare frequency, although the leukonychia remained unchanged. This case highlights the diagnostic importance of subtle nail findings in HHD. Early-onset or isolated leukonychia, often asymptomatic and easily overlooked, may precede cutaneous involvement and thus represent a valuable marker for early detection in at-risk individuals. Recognition of such signs can facilitate timely diagnosis, genetic counseling, and preventive management within affected families. Nail alterations in HHD appear long-lasting and independent of disease activity, underscoring their potential role as a stable phenotypic manifestation of this disorder. Early identification of these subtle nail changes can therefore improve patient outcomes by guiding early therapeutic intervention and reducing the delay in diagnosis often associated with this underrecognized condition.