Rheumatoid Arthritis (RA) diagnosis
Introduction
- RA = symmetric,
inflammatory, peripheral polyarthritis ที่ไม่ทราบสาเหตุ → ทำลายกระดูกอ่อนและกระดูก
→ functional loss, disability, CVD, osteoporosis, lymphoma
risk
- การวินิจฉัยเร็วและเริ่ม DMARDs แต่เนิ่น
ๆ ช่วยลด joint damage
- อาการระยะแรกมักคล้าย inflammatory arthritis อื่น
ๆ → ต้องใช้ clinical, serology, imaging
When to Suspect RA
- Constitutional
symptoms: weight loss, fatigue, asthenia, myalgia
- Morning
stiffness > 1 ชม. (hallmark ของ inflammatory
arthritis แต่ไม่ specific)
- Joint
manifestations: symmetric, small joints →
MCP, PIP, MTP; อาจเริ่มแบบ monoarthritis
- Lab:
ESR/CRP ↑, RF/anti-CCP
positive
- Imaging:
periarticular osteopenia, joint space narrowing, erosions (late)
Confirmatory Testing
1. Serology
- Rheumatoid
factor (RF)
- Sensitivity
~69%, Specificity ~85%
- High
titer (>3× ULN) →
more specific
- Positive
ล่วงหน้าได้หลายปี
- False
positive ใน SLE, Sjögren, chronic infection
- Anti-CCP
(ACPA)
- Sensitivity
~70–75%, Specificity >90%
- High
titer → highly
specific
- ช่วยแยก early undifferentiated arthritis
- Seronegative
RA
- ~20%
RF/ACPA negative → ต้องอาศัย clinical + imaging + response to therapy
2. Radiology
- X-ray
hands/feet: baseline; early →
soft tissue swelling, periarticular osteopenia; later → erosions, symmetric
narrowing
- US:
sensitive for synovitis, Doppler for inflammation, detect erosions > XR
- MRI:
detects bone marrow edema, early erosions, synovial hypertrophy → predictive of erosive
disease
Diagnostic Criteria
- 2010
ACR/EULAR Criteria →
definite RA if score > 6/10:
- Joints
involved (max 5 points)
- Serology
(RF, ACPA: 2–3 points)
- Acute
phase reactants ↑ (1
point)
- Symptoms
> 6 weeks (1 point)
- แต่ RA = clinical diagnosis → ต้องแยกจาก crystalline
arthritis, SLE, psoriatic arthritis ฯลฯ
Differential Diagnosis
Inflammatory
- Viral
arthritis – acute, self-limited; eg. hepatitis B, chikungunya
- Lyme
arthritis – oligoarthritis, knee dominant, endemic area
- Septic
arthritis – usually monoarticular, infection risk, synovial fluid cx+
- SLE/Sjögren/Overlap
CTD – systemic features, different autoantibodies
- Crystalline
arthritis (gout/CPPD) – episodic, self-limited, crystals in synovial
fluid
- PMR
(>50y) – shoulder/hip girdle pain, responds to low-dose steroids
- Reactive
arthritis – asymmetric, enthesitis, HLA-B27+, mucocutaneous signs
- IBD-associated
arthritis – polyarthritis with known/suspected IBD
- Psoriatic
arthritis – seronegative, DIP involvement, dactylitis, psoriasis
- Palindromic
rheumatism – episodic periarticular pain, may evolve into RA
- Sarcoid
arthropathy – arthritis + pulmonary sarcoid, ↑ACE
- Multicentric
reticulohistiocytosis – destructive arthritis + periungual nodules,
histology
Paraneoplastic/Drug-induced
- Hypertrophic
osteoarthropathy – clubbing, periosteal new bone
- MDS
(myelodysplasia) – seronegative, cytopenias
- ICI
therapy (immune checkpoint inhibitors) – RA-like arthritis
Non-inflammatory
- Osteoarthritis
(OA) – DIP + Heberden’s nodes, bony hard swelling, evening stiffness,
osteophytes
- Stenosing
tenosynovitis (trigger finger) – pain over tendon, no synovitis
- Carpal
tunnel syndrome – paresthesia, Tinel/Phalen+, may coexist with RA
- Hypermobility
syndrome – hyperextensible joints, no synovitis, normal labs
- Fibromyalgia
– widespread pain, tender points, no synovitis, normal ESR/CRP
Key Clinical Pearls
- RA
suspicion ↑ ถ้า symmetric polyarthritis (MCP, PIP, MTP) + morning
stiffness > 1 hr + RF/anti-CCP positive (ฝืดตอนเช้า /
ร้าวเกินสาม / ลามไปมือ / ถือสองข้าง / บ้าง nodule / Rheumatoid
factor positive)
- Serology
(RF, anti-CCP) ↑
specificity แต่ไม่แทน clinical exam
- Imaging
useful in early/subtle disease, esp. US/MRI
- Always
consider alternative inflammatory/noninflammatory causes → failure to respond to
DMARDs = ต้องทบทวนการวินิจฉัย
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