Disorders of Hyperpigmentation. Part I. Pathogenesis and clinical features of common pigmentary disorders.

Disorders of hyperpigmentation are common, and depending on the extent and location of involvement, can affect quality of life and pose a significant psychological burden for patients.1,2 Given the similarities in presentation of various causes of hyperpigmentation, it is often difficult to elucidate the etiology of these conditions, which is important to guide management.3,4 Furthermore, certain disorders such as lichen planus pigmentosus and ashy dermatosis have similar clinical and/or histologic presentations, and their classification as distinct entities has been debated, leading to additional confusion.5-7 In this review, the authors have selected commonly encountered disorders of hyperpigmentation of the skin, subdivided into epidermal, dermal, or mixed epidermal-dermal disorders based on the location of pigment deposition. along with disorders of hyperpigmentation of the mucosa and nails. Melanocytic nevi, genetic disorders, and systemic causes of hyperpigmentation were largely excluded and considered outside the scope of this review. We discuss the pathogenesis of hyperpigmentation, clinical features, and histology of these conditions, along with challenges encountered in diagnosis and classification. The second article in this two-part continuing medical education series focuses on medical and procedural treatments of hyperpigmentation.