Musculoskeletal and dermatology — RA, gout, skin cancers
**Osteoarthritis vs. rheumatoid arthritis:** • **OA** — weight-bearing joints (knees, hips), DIP (Heberden), PIP (Bouchard), asymmetric, worse with activity, radiography shows osteophytes + joint-space narrowing. • **RA** — symmetric polyarthritis, MCP/PIP spared DIP, morning stiffness >1 hr, anti-CCP (specific) + RF, ↑ESR/CRP. MTX first-line DMARD; TNF-α inhibitors, JAK inhibitors for refractory.
**Crystal arthropathies:** • **Gout** — MSU (negatively birefringent, needle-shaped). Podagra. Acute: NSAIDs, colchicine, steroids. Urate lowering: allopurinol, febuxostat, pegloticase (G6PD check pegloticase). • **Pseudogout (CPPD)** — rhomboid, positively birefringent. Chondrocalcinosis on X-ray.
**Seronegative spondyloarthropathies** (HLA-B27): ankylosing spondylitis (bamboo spine, uveitis), psoriatic arthritis (sausage digit, pencil-in-cup), reactive arthritis (Chlamydia, enteric post-infection; can't see/pee/climb tree), IBD-associated.
**Osteoporosis (USPSTF):** DEXA T-score ≤−2.5. Bisphosphonates (alendronate) first-line; denosumab, teriparatide (anabolic), romosozumab. Fall prevention, calcium (1200 mg) + vit D (800 IU).
**Skin cancers:** • **BCC** — most common; sun-exposed, pearly papule with telangiectasias; rarely metastasizes. • **SCC** — scaly hyperkeratotic; can metastasize; risk ↑ with HPV, immunosuppression, smoking, lip. • **Melanoma** — ABCDE (Asymmetry, Border, Color, Diameter >6 mm, Evolution). Depth (Breslow) is prognostic. BRAF V600E → targeted (dabrafenib + trametinib). Immune checkpoint inhibitors (nivolumab + ipilimumab, pembrolizumab).