Clinicopathological correlation of acquired hyperpigmentary disorders

Acquired pigmentary disorders are group of heterogenous entities that share single, most significant, clinical feature, that is, dyspigmentation. Asians and Indians, in particular, are mostly affected. Although the classic morphologies and common treatment options of these conditions have been reviewed in the global dermatology literature, the value of histpathological evaluation has not been thoroughly explored. The importance of accurate diagnosis is emphasized here as the underlying diseases have varying etiologies that need to be addressed in order to effectively treat the dyspigmentation. In this review, we describe and discuss the utility of histology in the diagnostic work of hyperpigmentary disorders, and how, in many cases, it can lead to targeted and more effective therapy. We focus on the most common acquired pigmentary disorders seen in Indian patients as well as a few uncommon diseases with distinctive histological traits. Facial melanoses, including mimickers of melasma, are thoroughly explored. These diseases include lichen planus pigmentosus, discoid lupus erythematosus, drug-induced melanoses, hyperpigmentation due to exogenous substances, acanthosis nigricans, and macular amyloidosis.