A 10-year-old girl complains of persistent redness of the skin over her knuckles and around the nail beds. She describes easy fatigability and can rise only with difficulty from a squatting position. Physical examination reveals erythema over the knuckles and a heliotropic rash. A muscle biopsy shows infiltrates of B and T lymphocytes around blood vessels and in connective tissue of the perimysium. Elevated serum levels of which of the following would be expected in this patient?

**Core Concept**
Juvenile dermatomyositis is an autoimmune disease characterized by inflammation of the muscles and skin. It involves the activation of T cells and B cells, which leads to the production of autoantibodies against various components of the muscle and skin.

**Why the Correct Answer is Right**
The elevated serum levels of muscle enzymes, particularly creatine kinase (CK), are expected in patients with juvenile dermatomyositis. This is due to the inflammatory damage to the muscle tissue, leading to the release of these enzymes into the bloodstream. The infiltration of lymphocytes around blood vessels and in connective tissue of the perimysium, as seen on muscle biopsy, further supports the diagnosis of an autoimmune-mediated muscle injury.

**Why Each Wrong Option is Incorrect**
* **Option A:** Elevated levels of lactate dehydrogenase (LDH) are not specific to juvenile dermatomyositis and can be seen in a variety of conditions, including malignancies and infections.
* **Option B:** Elevated levels of alanine transaminase (ALT) are not typically associated with juvenile dermatomyositis, as this condition primarily affects skeletal muscle rather than the liver.
* **Option D:** Elevated levels of erythrocyte sedimentation rate (ESR) are a non-specific marker of inflammation and can be seen in a wide range of conditions, including infections, autoimmune diseases, and malignancies.

**Clinical Pearl / High-Yield Fact**
The heliotropic rash, which gives the skin a bluish-purple hue, is a classic clinical finding in juvenile dermatomyositis. It is often seen over the eyelids, knuckles, and other areas of the body.

**Correct Answer:** C. Creatine kinase

✓ Correct Answer: D. Creatine kinase