Which of the following conditions presents as an acquired loss of pigmentation mainly on the back of the hands and face?

The condition that presents as an acquired loss of pigmentation mainly on the back of the hands and face is vitiligo. Vitiligo is characterized by the gradual depigmentation of patches on the skin due to the destruction of melanocytes, the cells responsible for producing melanin. This often results in well-defined white patches, particularly visible in areas exposed to the sun, such as the face and hands. The changes in pigmentation associated with vitiligo can be symmetrical and may develop over time, leading to a significant contrast with surrounding skin.

Other skin conditions listed may involve changes in pigmentation, but their presentations differ. For instance, pityriasis alba typically presents as hypopigmented patches but is often seen on a different distribution and usually involves more subtle skin changes rather than distinct white patches. Melasma involves hyperpigmented macules, typically due to hormonal changes and sun exposure, primarily affecting women, often on the face. Tinea versicolor, a fungal infection, can cause hypopigmented or hyperpigmented spots, which often appear more diffuse and are related to skin oil and climate rather than the immune response relevant to vitiligo. Thus, the distinguishing characteristics and typical presentation of vitiligo make it the correct answer in