Review Question - QID 215064

A 49-year-old woman presents to her primary care physician for arm weakness. The patient reports that over the course of 6 months, she has been having more difficulty putting groceries on the top shelf, combing her hair, and brushing her teeth. She denies any headache or vision changes, neck pain, or sensory changes. She has noticed a rash involving her face and both hands. She has no significant past medical history and takes no medications. Her family history is significant for her mother who died of metastatic breast cancer at the age of 63. Her temperature is 98.6°F (37.0°C), blood pressure is 115/70 mmHg, pulse is 70/min, and respirations are 12/min. On physical exam, the patient has an erythematous rash on her eyelids and around both eyes. She also has pink, violaceous papules over the interphalangeal and metacarpophalangeal joints on both of her hands. Strength testing is notable for 4-/5 strength in the deltoids, 4/5 in the biceps and triceps, and 5/5 in the wrist extensors and flexors and handgrip. Laboratory studies are shown below:

Serum:
Na+: 141 mEq/L
Cl-: 100 mEq/L
K+: 3.9 mEq/L
HCO3-: 25 mEq/L
Blood urea nitrogen (BUN): 15 mg/dL
Glucose: 105 mg/dL
Creatinine: 0.8 mg/dL
Thyroid-stimulating hormone (TSH): 2.6 µU/mL
Ca2+: 9.2 mg/dL
Aspartate aminotransferase (AST): 17 U/L
Alanine aminotransferase (ALT): 15 U/L
Creatine kinase (CK): 1350 IU/L

Which of the following is the most appropriate next step in management?