Confusable diagnoses · PANCE / PANRE

Rheumatoid Arthritis vs Psoriatic Arthritis

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

Rheumatoid Arthritis and Psoriatic 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.

Rheumatoid Arthritis vs Psoriatic Arthritis at a glance

  • Rheumatoid Arthritis: Chronic symmetric inflammatory polyarthritis with autoantibodies and erosive joint damage.
  • Psoriatic Arthritis: Seronegative inflammatory arthritis associated with psoriasis; classic features include dactylitis, enthesitis, and DIP involvement.

Try two board-style questions on Rheumatoid Arthritis vs Psoriatic Arthritis

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Question 1MusculoskeletalMedium
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.
Question 2MusculoskeletalMedium
A 50-year-old male with a 20-year history of plaque psoriasis develops asymmetric oligoarthritis affecting the distal interphalangeal (DIP) joints of both hands, with sausage digits (dactylitis) and nail pitting. Rheumatoid factor (RF) is negative. X-rays show periosteal reaction and pencil-in-cup deformity at the DIP joints. Which of the following is the most likely diagnosis?
  • APsoriatic arthritis
  • BGout
  • CRheumatoid arthritis
  • DReactive arthritis
Reveal answer & full explanation
Correct answer: A — Psoriatic arthritis
  • APsoriatic arthritis✓
  • BGout
  • CRheumatoid arthritis
  • DReactive arthritis

Why Psoriatic arthritis is correct

  • Psoriatic arthritis (PsA) is an inflammatory arthritis associated with psoriasis (skin precedes arthritis in 70%)
  • Diagnostic features: rheumatoid factor (RF) negative (seronegative), nail changes (pitting, onycholysis, oil drop sign), DIP involvement, X-ray features (periosteal reaction, enthesitis)
  • Dactylitis (sausage digit) reflects diffuse finger/toe swelling from tendon sheath inflammation, and pencil-in-cup deformity is characteristic

Why the others are wrong

  • Gout — causes acute monoarticular attacks with monosodium urate crystals and tophi, not dactylitis with nail pitting and pencil-in-cup change (confused-with crystal arthropathy)
  • Rheumatoid arthritis — is usually RF-positive and symmetric and spares the DIP joints, none of which fits here; dactylitis and pencil-in-cup change also point away from RA (anchoring on inflammatory arthritis)
  • Reactive arthritis — follows GI or GU infection with the conjunctivitis-urethritis-arthritis triad, not chronic psoriatic skin/nail disease (confused-with seronegative spondyloarthropathy)

Additional high-yield points

  • Patterns: (1) Distal interphalangeal (DIP) predominant (nail involvement common); (2) Asymmetric oligoarthritis; (3) Symmetric polyarthritis (rheumatoid arthritis (RA)-like); (4) Axial predominant (sacroiliitis); (5) Arthritis mutilans (severe destructive — pencil-in-cup)
  • Treatment: NSAIDs (nonsteroidal anti-inflammatory drugs) (mild); conventional synthetic disease-modifying antirheumatic drugs (csDMARDs) (methotrexate preferred for peripheral disease, leflunomide); biologics: anti-tumor necrosis factor (anti-TNF) (adalimumab, etanercept), interleukin-17 (IL-17) inhibitors (secukinumab, ixekizumab — effective for both skin and joints, avoid Inflammatory bowel disease (IBD)), IL-12/23 (ustekinumab), IL-23 (guselkumab, risankizumab)
  • Janus kinase (JAK) inhibitors (upadacitinib, tofacitinib): for inadequate biologic response
  • No hydroxychloroquine (ineffective for PsA, may worsen psoriasis)
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Side-by-side comparison

FeatureRheumatoid ArthritisPsoriatic Arthritis
At a glanceChronic symmetric inflammatory polyarthritis with autoantibodies and erosive joint damage.Seronegative inflammatory arthritis associated with psoriasis; classic features include dactylitis, enthesitis, and DIP involvement.
Classic presentationSymmetric 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;…Joint pain with morning stiffness >30 minutes, improving with activity; Asymmetric oligoarthritis (most common pattern), DIP-predominant, polyarticular RA-like pattern, arthritis mutilans, or axial pattern; Dactylitis — sausage digit from combined tenosynovitis and arthritis; Enthesitis — Achilles, plantar fascia, lateral epicondyle;…
Workup / key labs2010 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…CASPAR classification criteria: inflammatory articular disease (joint, spine, or entheseal) plus ≥3 points: current psoriasis (2 points) or personal/family history of psoriasis (1), psoriatic nail dystrophy (1), negative RF (1), current or past dactylitis (1), and juxta-articular new bone formation on radiograph (1).; RF and anti-CCP —…
ImagingPlain 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…Plain radiographs — 'pencil-in-cup' deformity at DIPs, periostitis, fluffy new bone formation, marginal erosions, ankylosis, asymmetric sacroiliitis, non-marginal syndesmophytes (large, asymmetric, parasyndesmophytes); Ultrasound or MRI — detects enthesitis, synovitis, dactylitis, and bone marrow edema before radiographic change
First-line treatmentEarly 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…Mild peripheral disease (oligoarthritis without poor prognostic factors): NSAIDs — naproxen, ibuprofen, meloxicam — plus intra-articular steroid injections; Conventional DMARDs for peripheral arthritis: methotrexate, sulfasalazine, leflunomide (also helps skin disease, especially MTX) — start promptly for polyarthritis, or for…

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Full outlines

Rheumatoid Arthritis (RA) Psoriatic Arthritis (PsA) 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.