A 42-year-old woman from Delhi presents to the dermatology clinic with a 3-year history of psoriasis vulgaris affecting her elbows and knees. Over the past 6 weeks, she has developed severe pain and swelling in her hands, wrists, and knees. Morning stiffness lasts 45 minutes. Laboratory investigations show elevated inflammatory markers (ESR 68 mm/hr, CRP 12 mg/dL). Rheumatoid factor and anti-CCP antibodies are negative. She denies any systemic symptoms. What is the most likely diagnosis?

Explanation

## Diagnosis: Psoriatic Arthritis ### Clinical Context This patient has a long-standing history of psoriasis vulgaris with recent onset of inflammatory joint disease. The combination of **cutaneous psoriasis + arthritis** in the setting of **negative rheumatoid factor and anti-CCP antibodies** is diagnostic of **psoriatic arthritis (PsA)**. **Key Point:** Psoriatic arthritis is a seronegative spondyloarthropathy that occurs in 5–30% of patients with psoriasis. It can precede, coincide with, or follow cutaneous manifestations. ### Diagnostic Criteria for Psoriatic Arthritis | Criterion | Present in This Case | Significance | |-----------|----------------------|--------------| | Established psoriasis | Yes (3 years) | Cutaneous disease predates arthritis | | Inflammatory polyarthritis | Yes (hands, wrists, knees) | Symmetric small and large joints | | Morning stiffness >30 min | Yes (45 minutes) | Indicates inflammatory arthritis | | Elevated inflammatory markers | Yes (ESR, CRP) | Active inflammation | | Negative RF and anti-CCP | Yes | Seronegative disease | | No systemic symptoms | Yes | Excludes systemic lupus erythematosus | ### Classification of Psoriatic Arthritis **High-Yield:** The **Moll and Wright criteria** (most widely used) require: 1. Inflammatory arthritis (peripheral joints and/or axial) 2. Psoriasis (current or past) 3. Negative rheumatoid factor 4. Radiographic evidence of juxta-articular osteolysis or pencil-in-cup deformity (in advanced cases) ### Patterns of PsA **Mnemonic: RAPID-PsA** - **R**asymmetric oligoarthritis (most common, ~70%) - **A**symmetric polyarthritis (mimics RA) - **P**rimary axial (spondylitis-like) - **I**nterphangeal (DIP joint involvement, unique to PsA) - **D**istal arthritis (DIP joints) This patient has **asymmetric polyarthritis**, the second most common pattern. ### Why This Is Not Other Diagnoses **Clinical Pearl:** Psoriatic arthritis is RF/anti-CCP negative, distinguishing it from rheumatoid arthritis. The presence of established psoriasis and DIP joint involvement (if present on imaging) are key differentiators. ### Management Implications 1. **NSAIDs** for symptom control 2. **DMARDs** (methotrexate is first-line, especially if cutaneous disease is active) 3. **Biologic agents** (TNF-α inhibitors, IL-17 inhibitors) for refractory disease 4. **Skin and joint assessment** at each visit (parallel treatment of both)