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**?

Explanation

## Why Dermatomyositis with mandatory age-appropriate malignancy screening is right Gottron papules—violaceous to erythematous papules and plaques over the extensor surfaces of the metacarpophalangeal (MCP) and interphalangeal (PIP, DIP) joints—are pathognomonic for dermatomyositis. The key distinguishing feature is their location OVER the knuckles (extensor joint surfaces), not between them. Combined with proximal muscle weakness and elevated CK, this clinical triad confirms dermatomyositis. The critical clinical anchor is that dermatomyositis carries a 15–25% association with underlying malignancy in adults (ovarian, lung, GI, NHL), making age-appropriate cancer screening mandatory at diagnosis and during follow-up. (Robbins 10e Ch 27; Harrison 21e Ch 358) ## Why each distractor is wrong - **Systemic lupus erythematosus with photosensitive malar rash and positive anti-dsDNA antibodies**: SLE presents with a malar "butterfly" rash, not Gottron papules. SLE does not produce violaceous papules over the MCP/PIP/DIP joints. The cutaneous finding described is specific to dermatomyositis, not SLE. - **Psoriasis vulgaris with lesions characteristically located between the knuckles on the dorsal fingers**: This is a classic distractor that tests the student's ability to distinguish Gottron papules from psoriatic lesions. Psoriasis typically affects the dorsum of fingers BETWEEN the joints, whereas Gottron papules are located directly OVER the extensor surfaces of the MCP/PIP/DIP joints. The anatomic distinction is critical. - **Rheumatoid arthritis with symmetric polyarticular involvement and positive rheumatoid factor**: RA causes symmetric joint inflammation and swelling, but does not produce the characteristic violaceous papules and plaques of Gottron papules. RA is a joint disease, not a dermatologic manifestation with this specific morphology. **High-Yield:** Gottron papules = pathognomonic for dermatomyositis; located OVER knuckles (not between them); always screen for occult malignancy in adult-onset dermatomyositis. [cite: Robbins 10e Ch 27; Harrison 21e Ch 358]