Review Question - QID 108982

A 25-year-old woman presents to her primary care physician with joint and muscle pain. She has a general aching/pain in her joints that lasts all day. The pain is constant and is not relieved by rest or activity. She also has pain in her hands at times and occasionally notices trouble swallowing when she is eating. She has a medical history of anxiety and is not currently taking any medications. Her temperature is 98.6°F (37°C), blood pressure is 115/72 mmHg, pulse is 74/min, and respirations are 11/min. On physical exam, the patient is a healthy young woman with a sunburn. Her hands are mildly edematous with the findings in Figure A. Laboratory values are below:

Serum:
Na+: 145 mEq/L
K+: 4.4 mEq/L
Cl-: 100 mEq/L
HCO3-: 24 mEq/L
BUN: 9 mg/dL
Glucose: 70 mg/dL
Creatinine: .7 mg/dL
Ca2+: 10 mg/dL
Mg2+: 1.8 mEq/L

Which of the following antibodies is most likely to aid in making the diagnosis in this patient?