Which condition is characterized by the absence of epidermal melanocytes leading to loss of pigmentation?

The condition characterized by the absence of epidermal melanocytes, resulting in a loss of pigmentation, is vitiligo. This autoimmune condition involves the destruction of melanocytes, which are the cells responsible for producing melanin, the pigment that gives color to the skin. As these cells are lost, areas of the skin become depigmented, leading to contrasting patches of lighter skin. This can occur on various parts of the body, including the face, neck, and hands, and is often more noticeable in individuals with darker skin.

Pityriasis alba, tinea versicolor, and melasma involve different mechanisms and characteristics. Pityriasis alba typically presents as hypopigmented patches, often in children, but it is related more to a disturbance in skin barrier function rather than a loss of melanocytes. Tinea versicolor is a fungal infection that leads to changes in pigmentation due to the effect of the fungus on skin cells, not due to the absence of melanocytes. Melasma, on the other hand, is associated with hormonal changes and typically appears as well-defined pigmented areas, particularly on the face, and is characterized by an overproduction of melanin rather than a loss of melanocytes.