Unveiling idiopathic guttate hypomelanosis: pathology, immunohistochemistry, and ultrastructural study

Background Idiopathic guttate hypomelanosis (IGH) is a pigment disorder of unknown etiology. Despite its high prevalence and the unaesthetic appearance of the lesions, there are relatively few histological studies on this disorder. This is an important gap to understanding its pathogenesis. Objectives To assess the microscopic structure of IGH lesions compared to normal adjacent skin areas and the possible interaction between melanocytes and the subjacent dermis. Methods In this cross‐sectional study, we took biopsy specimens of hypochromic lesions and adjacent normal skin from 20 patients with IGH. We analyzed the fragments using routine stains, immunohistochemistry, and electron microscopy. Results We found superficial dermal fibrosis in 90% (18/20) of our IGH cases and unreported keratinocyte cytoplasmic changes on electron microscopy. Conclusion Our results suggest an interaction between melanocytes and the subjacent dermis in IGH. These findings can help to understand melanocyte biology and the pathogenesis of other achromic lesions.