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OR5.1 | Inflammatory Arthritis — Practice Quiz
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A 32-year-old woman presents with a 3-month history of bilateral hand swelling, morning stiffness lasting more than 1 hour, and fatigue. Examination reveals boggy swelling of the MCP and PIP joints with sparing of the DIP joints. Which pair of investigations would most specifically confirm the diagnosis of rheumatoid arthritis?
Correct. RF and anti-CCP together confirm seropositive RA with high specificity. Anti-CCP is especially specific (~95%) and can be positive years before symptoms.
Rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies are the serological hallmarks of RA; anti-CCP has higher specificity (~95%) than RF alone. MCP/PIP involvement with DIP sparing is the classic joint distribution.
RA serological diagnosis rests on RF and anti-CCP. ANA/anti-dsDNA are for SLE; HLA-B27 is for spondyloarthropathies; uric acid/crystals are for gout.
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A 25-year-old male presents with insidious onset low back pain and stiffness, worse in the morning and improving with activity, for 8 months. He also reports right eye redness and photophobia. Pelvic X-ray shows blurring of sacroiliac joints bilaterally. Which HLA antigen is most strongly associated with this condition?
Correct. HLA-B27 is present in over 90% of patients with ankylosing spondylitis and is the key genetic association.
Ankylosing spondylitis is strongly associated with HLA-B27 (>90% of patients). Bilateral sacroiliitis on X-ray is the hallmark radiological finding. Associated uveitis (acute anterior uveitis) is the most common extra-articular feature.
The young male, inflammatory back pain improving with exercise, bilateral sacroiliitis, and anterior uveitis are classic features of ankylosing spondylitis, which is linked to HLA-B27.
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A 40-year-old man with longstanding psoriasis presents with asymmetric joint swelling involving the right index finger from the MCP to the DIP joint ('sausage digit'). X-ray shows erosion of the distal phalanx with pencil-in-cup deformity. What is the most likely diagnosis?
Correct. Psoriasis, dactylitis (sausage digit), DIP involvement, and pencil-in-cup deformity on X-ray are the defining features of psoriatic arthritis.
Psoriatic arthritis characteristically causes dactylitis ('sausage digit' = fusiform swelling of an entire digit due to tenosynovitis). The pencil-in-cup radiological deformity reflects osteolysis of the distal phalanx with cupping of the proximal phalanx — a hallmark of psoriatic arthritis arthritis mutilans pattern.
The combination of psoriasis, dactylitis, DIP joint involvement, and pencil-in-cup deformity points specifically to psoriatic arthritis.
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In a patient with established rheumatoid arthritis, examination reveals ulnar deviation of the fingers at the MCP joints and volar subluxation. This is best explained by which pathological process?
Correct. Pannus is the pathological hallmark of RA — inflamed synovium forms invasive granulation tissue that erodes cartilage and supportive ligaments, leading to the characteristic deformities.
The inflammatory pannus (vascular granulation tissue from the synovium) erodes cartilage, bone, and periarticular structures in RA. Destruction of collateral ligaments and intrinsic muscles leads to ulnar deviation at MCPs and volar subluxation — classic late-RA deformities.
RA deformities are caused by pannus formation, not crystal deposition (gout), weight-bearing sclerosis (OA), or periosteal reaction (osteomyelitis/tumour).
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A 30-year-old male with ankylosing spondylitis has progressive thoracic kyphosis and an X-ray spine showing anterior bridging syndesmophytes involving the entire thoracic and lumbar spine. What is this radiological appearance called?
Correct. 'Bamboo spine' describes the AP radiograph appearance of ankylosing spondylitis with complete spinal ankylosis from bridging syndesmophytes.
In advanced ankylosing spondylitis, ossification of the anterior longitudinal ligament and annulus fibrosus forms thin, vertical syndesmophytes bridging adjacent vertebral bodies. On AP view this produces the 'bamboo spine' appearance, pathognomonic of AS.
Bamboo spine is the pathognomonic AP X-ray appearance of advanced AS. The other options describe different pathologies entirely.
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A 45-year-old woman with 10 years of rheumatoid arthritis is being considered for disease-modifying antirheumatic drug (DMARD) therapy. Which of the following is the anchor DMARD used as first-line treatment in RA?
Correct. Methotrexate is the anchor DMARD for RA, used as first-line therapy. It is combined with other csDMARDs or biologics when needed.
Methotrexate is the anchor DMARD for RA — it is first-line, most extensively studied, and the backbone of combination DMARD regimens. It inhibits dihydrofolate reductase, suppressing purine synthesis and reducing inflammation. Folic acid supplementation is co-prescribed to reduce toxicity.
Indomethacin is an NSAID (symptom relief only); colchicine is used for gout; allopurinol is a urate-lowering agent for gout. Only methotrexate is a DMARD used in RA.
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A patient with rheumatoid arthritis has a seronegative result for RF but positive anti-CCP antibodies. What does this finding suggest about the prognosis?
Correct. Anti-CCP positivity counts as seropositive RA under current criteria and is associated with a more erosive, aggressive course — not a benign one.
Anti-CCP antibodies are more specific for RA than RF and are associated with a more erosive, aggressive disease course. Seronegative RF with positive anti-CCP still qualifies as seropositive RA (2010 ACR/EULAR criteria), and anti-CCP positivity predicts worse radiological outcome.
Anti-CCP is independently sufficient to classify seropositive RA under 2010 ACR/EULAR criteria. It confers a worse prognosis, not a better one.
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A 35-year-old male presents with right heel pain and tenderness at the Achilles tendon insertion, lower back stiffness worse in the morning, and a history of recent diarrhoeal illness. He is HLA-B27 positive. How does his joint disease differ from osteoarthritis?
Correct. The cardinal clinical distinction: inflammatory arthritis improves with activity (morning stiffness >1 hour, gel phenomenon, systemic features); OA worsens with activity and improves with rest.
Inflammatory arthritis (here, reactive/spondyloarthropathy) differs from degenerative osteoarthritis in that it is driven by synovial inflammation, affects young patients, improves with activity (morning stiffness >1 hour), and may involve entheses (enthesitis at Achilles), axial skeleton, and have systemic features. OA is mechanical, worsens with activity, and shows no inflammatory markers.
The key clinical distinction is the behaviour of stiffness — inflammatory arthritis shows prolonged morning stiffness that improves with movement, while OA produces brief stiffness (<30 min) that worsens with use.
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