A 35-year-old woman consults a physician because of increasing discomfo in her hands over the past year. Her symptoms have developed insidiously and are often worst for the first hour after rising. She has also been experiencing vague symptoms of fatigue and malaise, paicularly in the early afternoon. Physical examination of her hands is notable for tenderness and synol thickening of most of the small hand joints of both hands, paicularly the proximal interphalangeal and metacarpophalangeal joints. A number of joints elsewhere, including in the feet, elbows, and ankles, are also symmetrically involved. An autoantibody directed against lgG is detected in serum. Which of the following is the most likely diagnosis?

**Core Concept**
The patient's presentation of symmetrical polyarthritis, particularly affecting the small joints of the hands, along with systemic symptoms of fatigue and malaise, suggests an autoimmune inflammatory arthritis. The presence of an autoantibody directed against IgG is a key diagnostic clue.

**Why the Correct Answer is Right**
The autoantibody detected in the patient's serum is likely to be rheumatoid factor (RF), which is an autoantibody directed against the Fc region of IgG. Rheumatoid arthritis (RA) is a common autoimmune disease characterized by chronic inflammation of the joints, leading to pain, stiffness, and eventually, joint damage and deformity. The symptoms of RA often develop gradually, with a peak incidence in middle age, and are often worse in the morning or after periods of inactivity. The presence of RF is a diagnostic criterion for RA, although not all patients with RA test positive for RF.

**Why Each Wrong Option is Incorrect**
**Option A:** Psoriatic arthritis (PsA) typically presents with skin manifestations of psoriasis, such as erythematous plaques, and joint symptoms that are often asymmetric. While PsA can also involve the small joints of the hands, the presence of an autoantibody directed against IgG is not a characteristic feature of PsA.
**Option B:** Systemic lupus erythematosus (SLE) is an autoimmune disease that can affect multiple organ systems, including the skin, joints, kidneys, and nervous system. While SLE can present with arthritis, the presence of an autoantibody directed against IgG is not a specific diagnostic criterion for SLE.
**Option C:** Osteoarthritis (OA) is a degenerative joint disease that typically affects weight-bearing joints, such as the knees and hips, and is not characterized by the presence of an autoantibody directed against IgG.
**Option D:** Sjögren's syndrome is an autoimmune disease that primarily affects the exocrine glands, particularly the salivary and lacrimal glands, and can present with dry eyes and dry mouth. While Sjögren's syndrome can also involve the joints, the presence of an autoantibody directed against IgG is not a characteristic feature of Sjögren's syndrome.

**Clinical Pearl / High-Yield Fact**
Rheumatoid arthritis is a systemic disease that can affect multiple organ systems, including the skin, lungs, heart, and nervous system, in addition to the joints. Early recognition and treatment of RA are essential to prevent joint damage and deformity.

**Correct Answer:** C. Rheumatoid arthritis.

✓ Correct Answer: D. Rheumatoid ahritis