**Core Concept**
Dactylitis is a condition characterized by inflammation of an entire digit, often presenting as a swollen, painful finger or toe. It is commonly associated with conditions like psoriatic arthritis, reactive arthritis, and systemic lupus erythematosus. The underlying pathophysiology involves an autoimmune response and subsequent inflammation.

**Why the Correct Answer is Right**
Dactylitis is typically seen in conditions with a strong autoimmune component, such as psoriatic arthritis, where the immune system mistakenly attacks the joints and surrounding tissues. This leads to inflammation, swelling, and pain in the affected digit. The condition is often used as a diagnostic criterion for these autoimmune diseases.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because dactylitis can indeed be seen in osteoarthritis, although it is less common than in other autoimmune conditions. Osteoarthritis is a degenerative joint disease, and dactylitis in this context is typically a result of advanced joint damage and inflammation.

**Option B:** This option is incorrect because dactylitis can be seen in reactive arthritis, a type of arthritis that occurs as a reaction to an infection elsewhere in the body, often in the gastrointestinal tract or the urogenital tract. Reactive arthritis is an autoimmune response to the infection and can cause dactylitis.

**Option C:** This option is incorrect because dactylitis can be seen in systemic lupus erythematosus (SLE), a chronic autoimmune disease that can affect multiple organs and systems in the body. SLE can cause dactylitis due to inflammation and autoantibody production.

**Clinical Pearl / High-Yield Fact**
Dactylitis is often a "red flag" symptom for autoimmune diseases, particularly psoriatic arthritis. If a patient presents with dactylitis, it is essential to consider a comprehensive evaluation for underlying autoimmune conditions.

**Correct Answer:** D.