Which physical exam finding is most specific for systemic lupus erythematosus (SLE)?

The presence of a malar rash is considered the physical exam finding that is most specific for systemic lupus erythematosus (SLE). The malar rash, often referred to as a "butterfly rash," typically appears across the cheeks and nose, and is characterized by its distinctive shape and location. This rash is strongly associated with SLE and serves as one of the hallmark diagnostic criteria for the disease.

While swollen and painful joints, fatigue, myalgia, and stiffness with swelling of multiple joints can be seen in a variety of rheumatic and inflammatory conditions, they are less specific to SLE. These symptoms are broader and can overlap with other disorders such as rheumatoid arthritis, fibromyalgia, or various inflammatory arthritides. Therefore, although these findings may support a diagnosis of SLE, they are not definitive on their own.

In summary, the malar rash is a unique dermatological manifestation that can be closely tied to the autoimmune processes in systemic lupus erythematosus, making it a significant indicator for diagnosing the condition. Its specificity for SLE sets it apart from the more common and less distinct symptoms associated with other conditions.