This patient has striae distensae or stretch marks. The groin is a common area for developing stretch marks, and one of the main risks of topical glucocorticoids is the development of striae. Potential cutaneous complications associated with the use of topical glucocorticoids include thinning of the skin, development of striae, development of purpura, pigmentary changes (hypo- or hyperpigmentation), acneiform eruptions, and increased risk of infections. The risk increases when glucocorticoids are used for prolonged periods, are applied under occlusion or in skin folds where there is natural occlusion, or when high-potency glucocorticoids are applied to areas of thin skin, as in this patient. This patient was appropriately prescribed potent topical glucocorticoids for the control of his plaque psoriasis on his elbows and knees, but potent glucocorticoids are too strong for the groin and can rapidly lead to striae and atrophy.

Contact dermatitis typically has a geometric pattern in response to the area of contact with an allergen, and not along lines of stress as in this patient. Additionally, the skin is more edematous and often weeps serous fluid, and the area is intensely pruritic.

Inverse psoriasis refers to psoriatic changes occurring in intertriginous areas (as opposed to its more usual presence on extensor surfaces) where it can appear somewhat atypical, often lacking the characteristic surface scale because of the moistness of the skin creases. Inverse psoriasis results in broad areas of erythema confluent through the skin folds.

Tinea cruris presents as broad patches of erythema with fine scale (most often at the edges) and usually has a macerated appearance deep in the skin creases.