| The following vignette applies to the next 3 items |
A previously healthy 28-year-old Caucasian woman comes to the physician because of fatigue, arthralgias, and chest pain over the past 6 months. She has had a 2.3-kg (5-lb) weight loss during this period. She denies any recent travel or sick contacts. Her past medical history is insignificant. She takes no medications and has no known drug allergies. She is sexually active and uses condoms for contraception. She has never been pregnant. She does not use tobacco, alcohol, or drugs. Her mother has rheumatoid arthritis. Her temperature is 37.2 C (99 F), blood pressure is 122/77 mm Hg, and pulse is 78/min. Physical examination shows a faint facial rash. The lungs are clear to auscultation with mildly decreased breath sounds at the left lung base. The abdomen is soft and non-tender. There is no organomegaly. There is no peripheral edema. Neurologic examination is unremarkable.
Item 1 of 3
Which of the following tests is most likely to be positive in this patient?
The constellation of this patient's symptoms is most consistent with a diagnosis of systemic lupus erythematosus (SLE). Constitutional symptoms such as fatigue, arthralgias/myalgias, and weight loss are frequently present in SLE. Although not seen in this patient, fever is also a common systemic manifestation in SLE. The most telling clue in this patient is her facial rash, which likely represents the hallmark butterfly rash seen in many SLE patients after sun exposure. The decreased breath sounds at the left lung base are most likely a small pleural effusion secondary to SLE-related inflammation. The pleural effusion may cause pleuritis or chest pain (experienced by this patient).
Patients may have a family history of SLE or other connective tissue disorders. Testing for antinuclear antibodies (ANA) is indicated in patients who have suggestive symptoms and is positive in nearly all patients with SLE. However, ANA can also be positive in many patients who are healthy or who have connective tissue diseases other than SLE. Antibodies to double-stranded DNA (dsDNA), a subtype of ANA, are helpful because they are more specific for a diagnosis of SLE, and, with a sensitivity of 66-95%, are also the most sensitive of the listed antibodies to detect SLE.
(Choice B) Anti-centromere antibodies are most sensitive for the detection of the CREST variant of scleroderma.
(Choice C) Anti-mitochondrial antibodies are sensitive to detect primary biliary cirrhosis (PBC).
(Choice D) Anti-Smith antibodies are highly specific for SLE, but have a sensitivity of only 25% (versus anti-dsDNA antibodies, which have a sensitivity of approximately 70%).
(Choice E) Anti-Ro/SSA antibodies are seen in some patients with SLE but are most sensitive for Sjogren's syndrome.
Educational objective:
Although virtually all patients with SLE screen positive for antinuclear antibody (ANA), the test is nonspecific and can also be positive in healthy populations and in patients with connective tissue diseases. Both the anti-dsDNA and anti-Smith antibodies are associated with SLE, although anti-dsDNA antibodies are more sensitive at 66-95%.