What diagnosis is indicated by a well-circumscribed erythematous plaque with scales and fissuring on a patient's gluteal fold?

The presentation of a well-circumscribed erythematous plaque with scales and fissuring in a gluteal fold is highly indicative of psoriasis. Psoriasis is characterized by distinct, raised, red patches covered with thick, silvery scales. These plaques can occur in various locations on the body, including areas subject to friction or moisture, such as the gluteal folds. The appearance of fissuring is also consistent with the chronic nature of psoriasis, where skin can become thickened and cracked over time.

In contrast, while atopic dermatitis (eczema) also presents with erythema and scaling, it tends to be more itchy and is often associated with oozing lesions, especially in acute flare-ups. Ichthyosis is characterized by dry, scaly skin but lacks the inflammatory, well-defined plaque structure typical of psoriasis. Tinea corporis (ringworm) typically displays annular lesions with a clearer center and a raised border, often accompanied by pruritus, which is not characteristic of the plaque type seen in psoriasis.

Therefore, the specific features of a well-defined, erythematous plaque with scaling and associated fissuring strongly support a diagnosis of psoriasis.