**Core Concept**
The patient's presentation of joint pain and swelling in multiple joints, along with skin and nail changes, is suggestive of a systemic autoimmune condition. The presence of HLA-B27 positivity is a genetic marker often associated with spondyloarthropathies, a group of conditions characterized by inflammation of the axial skeleton and peripheral joints.

**Why the Correct Answer is Right**
The condition described is most likely Psoriatic Arthritis (PsA), a type of spondyloarthritis that occurs in patients with psoriasis. PsA is characterized by inflammation of the joints, skin, and sometimes the eyes, and is associated with HLA-B27 positivity. The joint involvement in PsA is typically asymmetric and can affect any joint, but the distal interphalangeal (DIP) joints are often involved. The characteristic radiographic features of PsA include:
* **Option C:** "Pencil-in-cup" deformity, which is a hallmark of PsA. This deformity is caused by the erosion of the joint surface, leading to a "pencil" appearance of the joint head and a "cup" appearance of the surrounding bone.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it describes a feature of Rheumatoid Arthritis (RA), which is characterized by symmetrical joint involvement and a different set of radiographic findings.
* **Option B:** This option is incorrect because it describes a feature of Osteoarthritis (OA), which is a degenerative joint disease that typically affects the weight-bearing joints and is not associated with HLA-B27 positivity.

**Clinical Pearl / High-Yield Fact**
PsA can be challenging to diagnose, as the skin and nail changes may precede the joint symptoms. A high index of suspicion is required, and a thorough physical examination and laboratory evaluation, including HLA-B27 testing, can help confirm the diagnosis.

**Correct Answer:** C. Pencil-in-cup deformity.