Musculoskeletal disorders 

Psoriatic arthritis is inflammatory arthritis in people with (or before) psoriasis, with asymmetric or distal joint involvement, dactylitis, enthesitis, nail changes and sometimes spinal disease. Treat with NSAIDs for mild disease, methotrexate with folic acid, sulfasalazine or leflunomide, and adalimumab or tofacitinib for severe or resistant disease, avoiding oral steroids in active psoriasis.

Axial spondyloarthritis is chronic inflammation of the sacroiliac joints and spine causing inflammatory back pain under 45 years that improves with activity, stiffness and progressive fusion, with uveitis, enthesitis and HLA-B27. Treat with daily exercises and physiotherapy, NSAIDs as first-line, and adalimumab if NSAIDs fail; conventional DMARDs do not help axial disease.

Reactive arthritis is sterile inflammatory arthritis 1–4 weeks after a gut (Salmonella, Shigella, Yersinia, Campylobacter) or genital (Chlamydia) infection, with asymmetric knee and ankle arthritis, enthesitis, urethritis and eye inflammation. Treat with NSAIDs, short steroids, doxycycline only for ongoing chlamydia, and sulfasalazine or methotrexate for chronic cases.

Enteropathic arthritis is seronegative spondyloarthritis with Crohn's disease or ulcerative colitis, affecting large peripheral joints and/or the spine, with enthesitis, uveitis and skin lesions. Control the bowel disease, use COX-2-selective NSAIDs briefly, sulfasalazine or methotrexate for peripheral arthritis, and adalimumab for severe or axial disease.

CPPD (pseudogout) is arthritis from calcium pyrophosphate crystals, with acute hot swollen knees, wrists or shoulders mimicking gout or infection, or a chronic OA-like form, often with metabolic causes. Treat flares with NSAIDs, colchicine or prednisolone, give colchicine prophylaxis for frequent attacks and correct metabolic causes; urate-lowering drugs do not help.