A 52-year-old woman presents with a 6-week history of progressive proximal muscle weakness affecting her shoulders and hips, along with difficulty climbing stairs. On examination, you observe violaceous papules and plaques over the dorsal surfaces of her metacarpophalangeal and interphalangeal joints, as marked **C** in the diagram. Her serum creatine kinase is 2400 U/L. Which of the following clinical features is MOST DIRECTLY associated with the cutaneous finding marked **C**?