What condition is characterized by flat-topped papules?

Lichen planus is characterized by flat-topped papules, also known as "papules with an indented top" or "planar" lesions. These papules are commonly found on the wrists, lumbar area, and oral mucosa. The lesions can appear purple or violaceous and are often associated with itching. Lichen planus is an inflammatory condition that involves the skin and mucous membranes, and it is distinct from other dermatological conditions due to its unique morphology and classic presentation.

In contrast, psoriasis typically presents with raised, scaly plaques rather than flat-topped papules, and these plaques are often erythematous with silvery white scales. Contact dermatitis usually manifests as vesicles, redness, and itching linked to exposure to allergens, showing more of an eczematous appearance. Acne vulgaris, on the other hand, is characterized by comedones, papules, pustules, and nodules, but they do not have the flat-topped appearance characteristic of lichen planus. Thus, the distinctive feature of flat-topped papules uniquely identifies lichen planus as the correct answer.