Confusable diagnoses · PANCE / PANRE

Osteoarthritis vs Pseudogout

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

Osteoarthritis and Pseudogout 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 Pseudogout at a glance

  • Osteoarthritis: Non-inflammatory degenerative joint disease driven by progressive articular cartilage loss.
  • Pseudogout: Acute crystal arthritis from calcium pyrophosphate deposition; classic site is the knee with chondrocalcinosis.

Try two board-style questions on Osteoarthritis vs Pseudogout

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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 67-year-old woman has acute knee pain and swelling. Arthrocentesis shows weakly positively birefringent rhomboid crystals. Which of the following is the most likely diagnosis?
  • AReactive joint arthritis
  • BPseudogout arthritis
  • CSeptic joint arthritis
  • DAcute gouty arthritis
Reveal answer & full explanation
Correct answer: B — Pseudogout arthritis
  • AReactive joint arthritis
  • BPseudogout arthritis✓
  • CSeptic joint arthritis
  • DAcute gouty arthritis

Why Pseudogout arthritis is correct

  • Calcium pyrophosphate crystals are rhomboid and weakly positively birefringent under polarized light.
  • The knee is the joint most often affected by CPPD in older adults.
  • The crystal morphology and birefringence directly identify pseudogout.

Why the others are wrong

  • Acute gouty arthritis — Gout shows needle-shaped, strongly negatively birefringent urate crystals; the described shape and birefringence are the opposite, a crystal-morphology trap.
  • Septic joint arthritis — Infection must always be excluded, but the synovial fluid shows diagnostic crystals rather than organisms or purulence, so septic arthritis is not the best answer here.
  • Reactive joint arthritis — Reactive arthritis follows a GI or GU infection and produces no crystals on synovial analysis.
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Side-by-side comparison

FeatureOsteoarthritisPseudogout
At a glanceNon-inflammatory degenerative joint disease driven by progressive articular cartilage loss.Acute crystal arthritis from calcium pyrophosphate deposition; classic site is the knee with chondrocalcinosis.
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,…Acute monoarticular or oligoarticular swelling, pain, and warmth — most often knee or wrist; Onset over hours to a day; often precipitated by surgery, trauma, or acute medical illness; Less severe than typical gout but can be incapacitating; Chronic forms: insidious polyarticular arthritis mimicking RA or OA; Warm, swollen joint with…
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…ACR/EULAR 2023 classification criteria for CPPD use clinical features + imaging + crystal identification.; Arthrocentesis with polarized microscopy — rhomboid or rod-shaped, POSITIVELY birefringent CPP crystals; inflammatory fluid; Gram stain and culture to exclude septic arthritis; Screen for underlying metabolic disease in patients…
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 — linear calcification within hyaline or fibrocartilage (chondrocalcinosis), classically in knee menisci, triangular fibrocartilage complex of wrist, symphysis pubis; Ultrasound — hyperechoic deposits within cartilage; DECT — less established than for gout
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…Acute flare: Intra-articular corticosteroid injection (triamcinolone 40 mg) — preferred when septic excluded, especially for knee; Acute flare: Oral NSAIDs — ibuprofen, naproxen, indomethacin (full anti-inflammatory dose, short course); Acute flare: Colchicine 1.2 mg, then 0.6 mg one hour later, then 0.6 mg BID-TID; Acute flare:…

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Full outlines

Osteoarthritis (OA) Pseudogout (CPPD Disease) 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.