Confusable diagnoses · PANCE / PANRE

Osteoarthritis vs Rheumatoid Arthritis

Written & clinically reviewed by Ryan Busch, PA-C · Updated August 2026 · Report an error

Osteoarthritis and Rheumatoid Arthritis are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.

Osteoarthritis vs Rheumatoid Arthritis at a glance

  • Osteoarthritis: Non-inflammatory degenerative joint disease driven by progressive articular cartilage loss.
  • Rheumatoid Arthritis: Chronic symmetric inflammatory polyarthritis with autoantibodies and erosive joint damage.

Try two board-style questions on Osteoarthritis vs Rheumatoid Arthritis

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Question 1MusculoskeletalEasy
A 50-year-old female has progressive pain and stiffness in both hands, particularly at the distal interphalangeal (DIP) and proximal interphalangeal (PIP) joints. Heberden nodes (DIP) and Bouchard nodes (PIP) are present. Grip strength is reduced. ESR and CRP are normal. Rheumatoid factor (RF) is negative. X-rays show joint space narrowing, subchondral sclerosis, and osteophytes. Which of the following is the most likely diagnosis?
  • AHand osteoarthritis
  • BSystemic lupus erythematosus
  • CPsoriatic arthritis
  • DRheumatoid arthritis
Reveal answer & full explanation
Correct answer: A — Hand osteoarthritis
  • AHand osteoarthritis✓
  • BSystemic lupus erythematosus
  • CPsoriatic arthritis
  • DRheumatoid arthritis

Why Hand osteoarthritis is correct

  • Distal interphalangeal (DIP) involvement with Heberden nodes and proximal interphalangeal (PIP) involvement with Bouchard nodes are classic for hand osteoarthritis
  • Normal inflammatory markers (ESR, CRP) and a negative rheumatoid factor (RF) argue against an inflammatory arthritis
  • X-ray changes of joint space narrowing, subchondral sclerosis, and osteophytes confirm the diagnosis

Why the others are wrong

  • Systemic lupus erythematosus — would show elevated inflammatory markers, ANA positivity, and multi-system involvement with a different joint pattern (confused-with inflammatory arthritis)
  • Psoriatic arthritis — can involve the DIP joints but is associated with psoriatic skin/nail changes and typically elevated inflammatory markers (anchoring on DIP involvement)
  • Rheumatoid arthritis — preferentially involves MCP and PIP joints with elevated ESR/CRP, erosions, and usually a positive RF (confused-with RA)

Additional high-yield points

  • American College of Rheumatology (ACR) 2019 first-line therapy: topical diclofenac
  • Additional options: oral NSAIDs, intra-articular steroids, and methotrexate for erosive hand OA (ACR 2026, conditional); hydroxychloroquine is strongly recommended against
  • Biologic disease-modifying antirheumatic drugs (DMARDs) and intra-articular hyaluronic acid are not recommended in hand osteoarthritis (OA)
Question 2MusculoskeletalMedium
A 55-year-old female with longstanding rheumatoid arthritis on methotrexate 20 mg weekly and etanercept for 4 years has persistent synovitis in 4 joints (Disease Activity Score 28 (DAS28) 4.2). She is adherent to therapy. Which of the following is the most appropriate next step in management?
  • ADiscontinue methotrexate
  • BSwitch etanercept to abatacept
  • CAdd infliximab to etanercept
  • DIncrease methotrexate to 25 mg weekly
Reveal answer & full explanation
Correct answer: B — Switch etanercept to abatacept
  • ADiscontinue methotrexate
  • BSwitch etanercept to abatacept✓
  • CAdd infliximab to etanercept
  • DIncrease methotrexate to 25 mg weekly

Why Switch etanercept to abatacept is correct

  • Inadequate response to an anti-tumor necrosis factor (TNF) agent after an adequate trial of 3–6 months calls for switching to a biologic with a different mechanism of action.
  • Abatacept provides T-cell co-stimulation blockade, a distinct mechanism from TNF inhibition.
  • Other non-TNF options include rituximab (anti-CD20, preferred in seropositive rheumatoid arthritis (RA)), interleukin-6 (IL-6) inhibitors (tocilizumab, sarilumab), and Janus kinase (JAK) inhibitors (tofacitinib, upadacitinib, baricitinib).
  • Before starting JAK inhibitors: screen for tuberculosis (TB) and hepatitis B virus (HBV); avoid in high cardiovascular (CV) risk per the ORAL Surveillance trial.

Why the others are wrong

  • Add infliximab to etanercept — Two biologics are never combined because infection risk rises without added benefit; after TNF-inhibitor failure, switching to a different mechanism is generally preferred over cycling to another TNF inhibitor.
  • Discontinue methotrexate — Methotrexate is an anchor DMARD in RA and should generally be continued; removing it would likely worsen disease control.
  • Increase methotrexate to 25 mg weekly — The patient has already had an inadequate response on combination therapy; escalating methotrexate dose alone is insufficient when biologic failure has occurred.
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Side-by-side comparison

FeatureOsteoarthritisRheumatoid Arthritis
At a glanceNon-inflammatory degenerative joint disease driven by progressive articular cartilage loss.Chronic symmetric inflammatory polyarthritis with autoantibodies and erosive joint damage.
Classic presentationHeberden nodes (DIP) and Bouchard nodes (PIP); squared first CMC joint; medial knee joint-line tenderness.; Insidious joint pain worse with activity and improved by rest; Brief morning stiffness (<30 minutes) and gel phenomenon after inactivity; Reduced range of motion, crepitus, functional limitation; Knee: medial joint-line pain,…Symmetric MCP/PIP/wrist swelling with positive MCP/MTP squeeze test, plus rheumatoid nodules in seropositive disease.; Insidious symmetric polyarthritis of small joints (MCP, PIP, wrists, MTPs); Morning stiffness lasting >1 hour, improving with activity; Fatigue, low-grade fever, weight loss; Hand weakness and difficulty with grip;…
Workup / key labsACR clinical criteria for knee OA: knee pain plus at least 3 of: age >50, stiffness <30 min, crepitus, bony tenderness, bony enlargement, no palpable warmth. Radiographic hallmarks (Kellgren-Lawrence): joint-space narrowing, subchondral sclerosis, subchondral cysts, marginal osteophytes.; Generally not required for diagnosis when…2010 ACR/EULAR classification: score ≥6 of 10 across (a) joint involvement, (b) serology (RF/anti-CCP), (c) acute-phase reactants, and (d) symptom duration ≥6 weeks classifies as RA.; RF and anti-CCP (anti-CCP higher specificity; both predict erosive disease); ESR and CRP (elevated, used to track activity); CBC (normocytic anemia of…
ImagingWeight-bearing plain radiographs of the affected joint — first-line; MRI reserved for atypical presentations, suspected meniscal or ligamentous injury, or possible avascular necrosis; Ultrasound can detect effusion and osteophytes but is not routinely neededPlain radiographs of hands and feet — periarticular osteopenia, symmetric joint-space narrowing, marginal erosions (MTPs often earliest); Ultrasound or MRI — more sensitive for early synovitis and erosions before plain-film changes; Cervical spine flexion/extension films in established disease to assess atlantoaxial subluxation prior to…
First-line treatmentPatient education and self-management programs; Exercise: low-impact aerobic, strengthening (quadriceps for knee OA), aquatic therapy; Weight loss (5-10% body weight) for knee or hip OA in overweight patients; a GLP-1 receptor agonist may be added to diet and exercise in knee OA with obesity (ACR 2026, conditional); Topical NSAIDs…Early DMARD therapy within 3 months of diagnosis — methotrexate is anchor drug; start 10-15 mg PO/SC weekly with folic acid 1 mg daily; Conventional DMARDs — methotrexate, hydroxychloroquine, sulfasalazine, leflunomide (often combined as 'triple therapy'); Bridging low-dose prednisone (≤10 mg/day) until DMARD takes effect; taper as…

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Full outlines

Osteoarthritis (OA) Rheumatoid Arthritis (RA) All 514 diagnoses

Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.