Rosh Internal Medicine Boost Practice Exam

In a patient with joint pain and positive anticitrullinated protein antibodies, what is the most likely diagnosis?

1. Gout

2. Polymyalgia rheumatica

3. Rheumatoid arthritis

4. Systemic lupus erythematosus

The correct answer is: Rheumatoid arthritis

In patients presenting with joint pain alongside the presence of positive anticitrullinated protein antibodies (ACPAs), rheumatoid arthritis emerges as the most likely diagnosis. ACPAs are significant biomarkers that are highly specific and sensitive for rheumatoid arthritis. Their presence suggests an autoimmune-mediated pathophysiology characteristic of this condition. Rheumatoid arthritis typically affects multiple joints symmetrically and is associated with inflammation and often leads to joint erosion over time. Joint pain can be accompanied by morning stiffness, and the patterns of joint involvement often help clinicians differentiate it from other types of arthritis. Gout is associated with monosodium urate crystal deposition and is characterized by sudden, severe pain in a single joint (often the big toe), which is not consistent with the symptomatology described. Polymyalgia rheumatica primarily affects older adults and is associated with muscle pain and stiffness rather than joint inflammation indicated by ACPAs. Systemic lupus erythematosus can involve joints but is characterized by a broader array of symptoms and specific laboratory findings that typically differ from those found in rheumatoid arthritis. Overall, the specific association between joint pain and positive ACPAs strongly points toward rheumatoid arthritis as the most probable diagnosis.