Granuloma Annulare in a Diabetic

A 47-year-old woman with type 2 diabetes mellitus on metformin and dapagliflozin presents with a 6-month history of asymptomatic annular plaques on the dorsal hands and fingers. She had tried topical clotrimazole without improvement. Examination reveals firm, raised, rope-like borders with central clearing. The feature marked **C** in the diagram—smooth surface with no epidermal change—is the key morphologic finding that distinguishes this condition from tinea corporis. Which of the following best explains why the absence of scale and epidermal disruption at the site marked **C** is diagnostically significant in granuloma annulare?