What is the most likely diagnosis for a patient presenting with worsening joint pain and a characteristic butterfly rash on the face?

The presence of worsening joint pain coupled with a characteristic butterfly rash on the face strongly suggests systemic lupus erythematosus (SLE). This condition is an autoimmune disease that can affect multiple systems in the body, and it is known for its distinctive facial rash that typically appears across the cheeks and nose, resembling a butterfly.

In SLE, patients often report symptoms such as joint pain and swelling, fatigue, skin rashes, and a variety of other systemic manifestations. The combination of these symptoms is particularly indicative of this disease, as SLE is one of the few autoimmune conditions where the butterfly rash is a hallmark feature.

Rheumatoid arthritis primarily causes joint pain and stiffness but does not typically present with a butterfly rash. Psoriasis is associated with skin changes and can include joint pain (psoriatic arthritis), but the rashes seen in psoriasis differ significantly in appearance from the butterfly rash of lupus. Dermatomyositis involves skin manifestations and muscle weakness but does not generally present with the specific pattern and characteristics of the facial rash observed in SLE.

Thus, considering the combination of joint pain and the characteristic rash, systemic lupus erythematosus is the most likely diagnosis.