Which symptom is primarily associated with Systemic Lupus Erythematosus (SLE)?

The butterfly rash, also known as a malar rash, is a distinctive symptom primarily associated with Systemic Lupus Erythematosus (SLE). This rash typically appears across the cheeks and over the bridge of the nose, resembling the shape of a butterfly. It is a hallmark sign of SLE and can be a significant indicator for diagnosis, as it often occurs after sun exposure and may be accompanied by other systemic manifestations of the disease.

In contrast, morning stiffness is more commonly associated with conditions like rheumatoid arthritis and is not exclusive to SLE. Osteoarthritis primarily involves degeneration of cartilage and results in joint pain, but does not have the systemic implications seen in SLE. Joint swelling can occur in a variety of conditions, including arthritis and other inflammatory diseases, and is not distinctive to SLE. Thus, while joint swelling can be a symptom of SLE, it does not serve as a key diagnostic feature, unlike the butterfly rash.