MCQ – 87831

A 34-year-old woman has had increasing lethargy for the past 8 months. During this time, she has experienced increased sensitivity to sunlight, and now rarely goes outdoors during the day. She has pain in her hands, elbows, knees, and feet, and muscle aches in her arms and legs. She has had increasing dyspnea for the past week. Physical examination shows no joint deformities, swelling, or redness. On auscultation of the chest, a friction rub is audible. A chest radiograph shows bilateral pleural effusions. Laboratory findings show hemoglobin, 11.6 mg/dL; hematocrit, 34.3%; MCV, 84 μm3; platelet count, 133,400/mm3; WBC count, 4610/mm3; Na+, 140 mmol/L; K+, 4 mmol/L; Cl−, 99 mmol/L; CO2, 25 mmol/L; glucose, 80 mg/dL; creatinine, 2.4 mg/dL; and calcium, 7.9 mg/dL. Which of the following additional laboratory tests would be most helpful to diagnose her underlying condition?

Correct Answer � D Explanation

 Answer : D Antinuclear antibody

• The patient has findings consistent with systemic lupus erythematosus (SLE): photosensitivity, renal failure, body cavity effusions, pericarditis, arthralgias, myalgias, and cytopenias. 

• The antinuclear antibody test is the most sensitive screening test for SLE, and if positive can be followed by the more specific anti–double-stranded DNA antibody test.

• Acetylcholine receptor antibody may be seen in myasthenia gravis, which would explain muscle weakness but not pain.

• Anti–DNA topoisomerase is seen in scleroderma, in which there is renal failure and skin thickening, but not photosensitivity. 

• Anti–glomerular basement membrane antibody can be seen in Goodpasture syndrome and renal failure, but not arthralgias, myalgias, or cytopenias. 

• Antimicrosomal (anti–thyroid peroxidase) antibody is associated with autoimmune thyroid diseases, mainly Hashimoto thyroiditis, but also Graves disease. Antimitochondrial antibody may be seen in primary biliary cirrhosis, which leads to malaise, but not to renal failure or photosensitivity.