A 23-year-old previously healthy woman comes to the clinic due to a 3-month history of intermittent hand stiffness and pain. She has also felt excessively tired and has had occasional episodes of knee and sharp chest pain. The patient takes no medications and does not use tobacco, alcohol, or illicit drugs. Temperature is 37.2 C (99 F), blood pressure is 130/70 mm Hg, and pulse is 80/min. Bilateral hand joints and wrists are mildly tender and swollen. Lungs are clear to auscultation and heart sounds are normal. The abdomen is soft and nontender with no organomegaly. There is mild bilateral lower extremity edema. The patient has no rash or lymphadenopathy. Laboratory results are as follows:
| Hemoglobin | 12.2 g/dL |
| Platelets | 98,000/mm3 |
| Leukocytes | 3,300/mm3 |
| Creatinine | 0.8 mg/dL |
| Urinalysis | 2+ protein, 5-10 erythrocytes/hpf |
Which of the following is the best next step in establishing the diagnosis?
Rheumatologic diseases & commonly associated autoantibodies | ||
Sensitivity (%) | Specificity (%) | |
Rheumatoid arthritis | RF: 70-80 | Anti-CCP: 95 |
Systemic lupus erythematosus | ANA: 95 | Anti-dsDNA/anti-Sm: 96 |
Drug-induced lupus | ANA: 95 | Antihistone: 95 |
Diffuse systemic sclerosis | ANA: 95 | Anti–Scl-70: 99 |
Limited systemic sclerosis | ANA: 95 | Anticentromere: 97 |
Polymyositis/dermatomyositis | ANA: 75 | Anti–Jo-1: 99 |
ANA = antinuclear antibodies; anti-CCP = anti–cyclic citrullinated peptide; anti-dsDNA = anti–double-stranded DNA; anti–Scl-70 = anti–topoisomerase I; anti-Sm = anti-Smith; RF = rheumatoid factor. | ||
This patient has a symmetric polyarthritis (ie, pain, stiffness, tenderness) associated with possible serositis (ie, sharp chest pain). In the context of systemic features (eg, fatigue), mild cytopenias (leukopenia, thrombocytopenia), and protein-losing nephropathy (edema, proteinuria, microscopic hematuria), this presentation is suspicious for systemic lupus erythematosus (SLE). Initial evaluation of SLE should include a complete blood count, renal function studies (ie, urinalysis, serum creatinine), and serum complement levels (eg, C3, C4).
In addition, autoantibody studies are recommended to support the diagnosis. An antinuclear antibody (ANA) titer is very sensitive (95%-100%) for SLE and should be obtained as the initial first-order test. However, ANA is not specific and can be elevated in other autoimmune disorders and in up to 20% of healthy women. If the ANA test is positive, more specific confirmatory tests such as anti–double-stranded DNA and anti-Sm (Smith) antibodies can be obtained. However, these second-order assays are much less sensitive than ANA and are not recommended as initial tests, although some laboratories offer them as reflex tests if the ANA test is positive.
(Choice A) Cyclic citrullinated peptide antibodies are specific for rheumatoid arthritis, which causes a symmetric polyarthritis, but nephropathy (eg, hematuria, proteinuria) is uncommon.
(Choice B) Antihistone antibodies are specific for drug-induced lupus. This patient is not taking medications associated with drug-induced lupus (eg, hydralazine, procainamide, minocycline), and drug-induced lupus is not usually associated with nephropathy.
(Choice C) Anti–neutrophil cytoplasmic antibodies are associated with a number of vasculitic disorders, especially granulomatosis with polyangiitis. This condition can cause glomerulonephritis and arthralgias, but most patients also have upper (eg, epistaxis, nasal ulcers) or lower (eg, wheezing, hemoptysis) respiratory features.
(Choice E) Anti-Ro/SSA antibodies are classically associated with Sjögren syndrome (eg, dry eyes, xerostomia). They are seen in some patients with SLE and confer an increased risk of neonatal lupus syndrome due to transplacental passage of the antibodies. However, anti-Ro has low sensitivity for SLE and is not done as an initial test.
(Choice F) Anti–Scl-70 (anti-topoisomerase) antibodies have moderate sensitivity and high specificity for systemic sclerosis (scleroderma) and are associated with extensive skin involvement and interstitial pulmonary fibrosis.
Educational objective:
Antinuclear antibody (ANA) is a very sensitive, but nonspecific, marker for systemic lupus erythematosus. If ANA titers are elevated, more specific autoantibodies (eg, anti–double-stranded DNA) can confirm the diagnosis.