Confusable diagnoses · PANCE / PANRE

Rheumatoid Arthritis vs Systemic Lupus Erythematosus

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

Rheumatoid Arthritis and Systemic Lupus Erythematosus 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 Systemic Lupus Erythematosus at a glance

  • Rheumatoid Arthritis: Chronic symmetric inflammatory polyarthritis with autoantibodies and erosive joint damage.
  • Systemic Lupus Erythematosus: Multisystem autoimmune disease with autoantibodies against nuclear antigens and immune-complex tissue injury.

Try two board-style questions on Rheumatoid Arthritis vs Systemic Lupus Erythematosus

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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 29-year-old woman with systemic lupus erythematosus on hydroxychloroquine returns with 2 weeks of worsening fatigue, lower-extremity swelling, and foamy urine. Blood pressure is 152/96 mm Hg and there is 2+ pedal edema. Urinalysis shows 3+ protein and red cell casts, and the urine protein-to-creatinine ratio is elevated. Which of the following laboratory findings best supports active lupus nephritis as the cause of her presentation?
  • ARising anti-double-stranded DNA titer with falling C3 and C4
  • BElevated C-reactive protein with a normal serum complement level
  • CPositive antinuclear antibody at a 1:160 titer on screening
  • DHigh-titer anti-Smith antibody with normal C3 and C4 levels
Reveal answer & full explanation
Correct answer: A — Rising anti-double-stranded DNA titer with falling C3 and C4
  • ARising anti-double-stranded DNA titer with falling C3 and C4✓
  • BElevated C-reactive protein with a normal serum complement level
  • CPositive antinuclear antibody at a 1:160 titer on screening
  • DHigh-titer anti-Smith antibody with normal C3 and C4 levels

Why Rising anti-double-stranded DNA titer with falling C3 and C4 is correct

  • Anti-dsDNA is specific for SLE, and its titer correlates with disease activity, particularly lupus nephritis; a rising titer signals an active flare.
  • Complement (C3, C4) is consumed by immune-complex deposition during active disease, so falling levels track worsening nephritis.
  • Combined with the proteinuria and red cell casts, this serologic pattern best supports active renal involvement (renal biopsy remains definitive for ISN/RPS class).

Why the others are wrong

  • Positive antinuclear antibody at a 1:160 titer on screening: ANA is a sensitive screen (sensitivity >95%) but is nonspecific and does not track activity; it is expected in nearly all SLE patients and cannot confirm a flare.
  • High-titer anti-Smith antibody with normal C3 and C4 levels: anti-Smith is highly specific for diagnosing SLE, but its level does not correlate with activity, and normal complement argues against active immune-complex nephritis.
  • Elevated C-reactive protein with a normal serum complement level: CRP is typically normal in active SLE, so an elevated CRP should instead raise concern for infection or serositis, and normal complement argues against active nephritis.
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Side-by-side comparison

FeatureRheumatoid ArthritisSystemic Lupus Erythematosus
At a glanceChronic symmetric inflammatory polyarthritis with autoantibodies and erosive joint damage.Multisystem autoimmune disease with autoantibodies against nuclear antigens and immune-complex tissue injury.
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;…Constitutional: fatigue, low-grade fever, weight loss; Mucocutaneous: malar (butterfly) rash sparing nasolabial folds, discoid lesions, photosensitivity, oral or nasal ulcers (often painless), nonscarring alopecia; Musculoskeletal: symmetric small-joint polyarthralgia/arthritis, typically nonerosive (Jaccoud arthropathy if deforming);…
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…EULAR/ACR 2019 classification criteria: ANA ≥1:80 as entry, then weighted clinical and immunologic domains (total ≥10 points classifies).; ANA — screening test; sensitivity >95% but low specificity; Anti-dsDNA — specific; titer correlates with disease activity (especially nephritis); Anti-Smith — highly specific; Anti-Ro/SSA,…
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…Renal biopsy — definitive for lupus nephritis classification (ISN/RPS classes I-VI); guides immunosuppression; Echo if pericardial effusion or Libman-Sacks endocarditis suspected; MRI brain for neuropsychiatric SLE workup
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…Sun protection and smoking cessation for all patients; Hydroxychloroquine ≤5 mg/kg actual body weight/day (usually 200-400 mg/day) — foundational for all SLE; reduces flares, organ damage, and mortality (baseline eye exam, annually after 5 years); NSAIDs — ibuprofen, naproxen — for mild musculoskeletal or serositis symptoms (caution…

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Full outlines

Rheumatoid Arthritis (RA) Systemic Lupus Erythematosus (SLE) 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.