Answer:

Patches of erythematous scaly plaques on knuckles in patients with dermatomyositis.

KEY POINTS: SIGNIFICANCE OF LAB VALUES IN RHEUMATOLOGIC DISEASE

1. ANA titers are not associated with intensity of disease.
2. Measurement of single-stranded DNA antibodies are of absolutely no clinical value.
3. The HLA B27 association with arthritis is highest in AS and reactive arthritis but lower with the spondylitis associated with psoriasis and inflammatory bowel disease.
4. A patient with low positive RF and arthralgia should be checked for hepatitis C, which can produce a low-grade synovitis and cryoglobulins (which, in turn, can produce a falsely positive RF).
5. Serum transaminases (ALT, AST) are found in muscle. Therefore, elevated LFTs, especially when no concomitant gamma-glutamyl transferase is available, may reflect muscle inflammation in a patient with rheumatic disease. Check the creatine phosphokinase level.

Reference: Hochberg MC (ed). Rheumatology, 3rd ed. St. Louis, Mosby, 2003.

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