Inflammatory Joint Diseases: RA, Spondyloarthritis and Crystal Arthritis
Rheumatoid arthritis
Symmetrical small-joint (MCP, PIP, wrist) synovitis with prolonged morning stiffness and sparing of the DIP joints. Extra-articular disease matters for exams: rheumatoid nodules, interstitial lung disease, scleritis, mononeuritis multiplex, and cervical spine instability (ask about neck pain before intubation). Treat early with disease-modifying drugs; methotrexate is usually first line, with biologics or targeted synthetic drugs added for inadequate response. Assess disease activity with composite scores and remember that radiographic erosions appear late.
Spondyloarthritis
Axial spondyloarthritis presents with inflammatory back pain: onset before 40, insidious, improving with exercise, with night pain and stiffness. Enthesitis (Achilles, plantar fascia), dactylitis, uveitis, psoriasis and inflammatory bowel disease are key associations. Sacroiliitis on imaging plus HLA-B27 supports the diagnosis. Peripheral spondyloarthritis is often asymmetrical and lower limb predominant.
Crystal arthritis
Gout: acute monoarthritis, classically first MTP joint, with negatively birefringent needle-shaped crystals. Risk factors include diuretics, renal impairment, alcohol and metabolic syndrome. Do not start or stop urate-lowering therapy during a flare without careful thought; cover with prophylaxis. Pseudogout (calcium pyrophosphate deposition) affects larger joints such as the knee and wrist in older adults, with positively birefringent rhomboid crystals and chondrocalcinosis on radiographs.
Question traps
- Symmetrical DIP involvement suggests osteoarthritis or psoriatic arthritis, not rheumatoid arthritis.
- Septic arthritis can mimic a flare; aspirate when in doubt.
- Inflammatory back pain is defined by pattern, not by a positive HLA-B27.
Rule of thumb
Acute monoarthritis plus fever equals aspirate and culture, whatever the crystal result shows.