Musculoskeletal · PANCE / PANRE

Psoriatic Arthritis (PsA)

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

Seronegative inflammatory arthritis associated with psoriasis; classic features include dactylitis, enthesitis, and DIP involvement.

Also known as: PsA, psoriatic arthritis

Overview

Inflammatory arthritis occurring in patients with cutaneous or nail psoriasis. A heterogeneous disease that can affect peripheral joints (including DIPs), entheses, the axial skeleton, and digits (dactylitis), often in asymmetric patterns.

Epidemiology

Develops in 20-30% of patients with psoriasis. Skin disease usually precedes joint disease by years, but arthritis can appear first in 10-15%. Onset peaks 30-50; men and women affected roughly equally (axial disease more common in men).

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Question 1MusculoskeletalMedium
A 42-year-old man presents with a 4-month history of pain and stiffness in the distal interphalangeal joints of both hands and the right knee. He reports morning stiffness lasting about 90 minutes. PMH is significant for plaque psoriasis affecting his elbows and scalp for 10 years. Exam shows dactylitis of the right second toe, pitting of several fingernails, and scaly erythematous plaques on the extensor surfaces. ESR is elevated; rheumatoid factor and anti-CCP are negative. Hand radiographs show erosive changes at the DIP joints. Which of the following is the most appropriate first-line pharmacologic therapy?
  • AAdalimumab
  • BPrednisone
  • CHydroxychloroquine
  • DMethotrexate
Reveal answer & full explanation
Correct answer: D — Methotrexate
  • AAdalimumab
  • BPrednisone
  • CHydroxychloroquine
  • DMethotrexate✓

Why methotrexate is correct

  • This patient has psoriatic arthritis (PsA) with peripheral joint involvement, dactylitis, nail pitting, and concurrent plaque psoriasis.
  • For peripheral PsA with moderate-to-severe disease activity, conventional synthetic DMARDs (csDMARDs) are first-line.
  • Methotrexate is the most commonly used initial agent because it treats both the joint disease and the cutaneous psoriasis, is oral, and is inexpensive.
  • Typically dosed at 15–25 mg weekly with folic acid supplementation.
  • GRAPPA and EULAR guidelines support methotrexate as a preferred initial conventional synthetic DMARD in peripheral PsA with clinically relevant skin involvement, with a biologic escalated to after inadequate response to a csDMARD.

Why the others are wrong

  • A) Adalimumab — a TNF inhibitor that is highly effective in PsA but is generally reserved for patients who fail or cannot tolerate a conventional DMARD, or for those with axial disease, severe enthesitis, or rapidly erosive disease; not first-line here.
  • B) Prednisone — systemic glucocorticoids are generally avoided in PsA because tapering can precipitate a severe pustular or erythrodermic psoriasis flare; used only sparingly for short bridging.
  • C) Hydroxychloroquine — used in rheumatoid arthritis and lupus but is relatively contraindicated in psoriasis because it can trigger psoriatic flares and erythroderma.
Question 2MusculoskeletalMedium
A 55-year-old man with a long history of plaque psoriasis develops pain and swelling in several finger and toe joints. Examination shows an asymmetric oligoarthritis with involvement of the distal interphalangeal joints and a diffusely swollen 'sausage' digit. Radiographs of the hands demonstrate a pencil-in-cup deformity, and rheumatoid factor is negative. Which of the following is the most likely diagnosis?
  • APsoriatic arthritis
  • BGouty arthropathy
  • CRheumatoid arthritis
  • DReactive arthritis
Reveal answer & full explanation
Correct answer: A — Psoriatic arthritis
  • APsoriatic arthritis✓
  • BGouty arthropathy
  • CRheumatoid arthritis
  • DReactive arthritis

Why Psoriatic arthritis is correct

  • Psoriatic arthritis classically occurs in a patient with cutaneous psoriasis and produces an asymmetric oligoarthritis with distal interphalangeal (DIP) involvement, dactylitis (the 'sausage' digit), and enthesitis.
  • The pencil-in-cup deformity is its characteristic erosive radiographic finding, and rheumatoid factor is typically negative (a seronegative spondyloarthropathy).
  • The combination of psoriasis, DIP disease, dactylitis, pencil-in-cup change, and negative rheumatoid factor distinguishes it from the other inflammatory arthritides.

Why the others are wrong

  • Gouty arthropathy — gout produces 'rat-bite' or overhanging erosions and tophi rather than the pencil-in-cup deformity, and typically begins as acute monoarticular podagra (confused-with erosive pattern).
  • Rheumatoid arthritis — RA is symmetric, characteristically spares the DIP joints, and is usually rheumatoid factor positive, the opposite of this asymmetric, DIP-predominant, seronegative picture (premature closure on the most common inflammatory arthritis).
  • Reactive arthritis — reactive arthritis follows a genitourinary or gastrointestinal infection and lacks psoriasis and the pencil-in-cup deformity (buzzword-matching on oligoarthritis).
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Risk factors

  • Cutaneous psoriasis (especially severe or with nail involvement)
  • Family history of psoriasis or psoriatic arthritis
  • HLA-B27 (axial PsA)
  • Obesity (worsens disease and reduces drug response)
  • Smoking
  • Trauma (Koebner phenomenon in joints — deep Koebner)

Pathophysiology

Combined synovitis and enthesitis driven by TNF-alpha, IL-17, and IL-23 pathways. Genetic susceptibility (HLA-B27, HLA-Cw6, IL-23R variants) plus environmental triggers produce inflammation at synovium, entheses, nails, and skin.

Clinical presentation

Symptoms

  • 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
  • Heel pain, low back pain (inflammatory pattern)
  • Skin and nail findings — plaque psoriasis (look for hidden sites: scalp, umbilicus, gluteal cleft, behind ears) and nail pitting, onycholysis, oil drop sign

Signs / physical exam

  • Asymmetric synovitis often involving DIPs
  • Dactylitis — entire digit swollen, tender
  • Enthesitis at Achilles insertion, plantar fascia, patellar insertion
  • Nail changes: pitting, onycholysis, subungual hyperkeratosis
  • Skin plaques
  • Reduced spinal mobility if axial involvement

Differential diagnosis

  • Rheumatoid arthritis — Symmetric MCP/PIP/wrist synovitis, positive RF/CCP, no DIP unless OA also present; no enthesitis or dactylitis
  • Osteoarthritis (especially erosive hand OA) — DIP involvement with Heberden nodes, mechanical pattern, normal CRP
  • Gout — Acute monoarticular flares, MSU crystals, can mimic PsA in feet
  • Reactive arthritis — Post-infectious oligoarthritis, conjunctivitis, urethritis; HLA-B27
  • Ankylosing spondylitis — Pure axial disease without psoriasis or skin findings
  • IBD-associated arthritis — Coexisting Crohn or UC; peripheral or axial pattern

Diagnostic workup

Diagnostic criteria

CASPAR classification criteria: inflammatory articular disease (joint, spine, or entheseal) plus ≥3 points from psoriasis, nail changes, RF-negative, dactylitis history, and juxta-articular new bone formation.

Labs

  • RF and anti-CCP — typically NEGATIVE (some patients have low-titer positivity)
  • ESR, CRP — variably elevated; can be normal in active disease
  • HLA-B27 — supportive in axial disease
  • Uric acid — exclude gout in monoarticular flare

Imaging

  • 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

Diagnostic algorithm

FeatureRAPsA
SymmetrySymmetricOften asymmetric
DIP involvementRareCommon
DactylitisNoYes (hallmark)
EnthesitisNoYes (hallmark)
RF / anti-CCPPositive 70-80%Typically negative
Nail changesNoPitting, onycholysis
RadiographMarginal erosions, periarticular osteopeniaPencil-in-cup, periostitis, new bone
Axial diseaseCervical only (C1-C2)Sacroiliitis (often asymmetric), syndesmophytes
Differentiating RA from PsA — the high-yield boards comparison.

Treatment

First-line

  • Mild peripheral disease: NSAIDs — naproxen, ibuprofen, meloxicam — plus intra-articular steroid injections
  • Conventional DMARDs for peripheral arthritis: methotrexate, sulfasalazine, leflunomide (also helps skin disease, especially MTX)
  • Treat skin disease in parallel with topical agents and phototherapy as needed

Second-line / adjunct

  • TNF inhibitors — etanercept, adalimumab, infliximab, golimumab, certolizumab — broadly effective for skin, joint, axial, and entheseal disease
  • IL-17 inhibitors — secukinumab, ixekizumab — particularly effective for skin and enthesitis (avoid in IBD)
  • IL-23 inhibitors — guselkumab, risankizumab — emerging first-line biologic for skin and joints
  • IL-12/23 inhibitor — ustekinumab
  • JAK inhibitors — tofacitinib, upadacitinib
  • PDE4 inhibitor — apremilast — modest efficacy, well-tolerated oral option
  • Avoid systemic corticosteroids when possible — withdrawal can trigger pustular psoriasis

Complications

  • Joint destruction, arthritis mutilans (telescoping digits)
  • Functional disability and reduced quality of life
  • Comorbidities: cardiovascular disease, metabolic syndrome, obesity, fatty liver, depression, uveitis, IBD
  • Increased cardiovascular mortality independent of traditional risk factors

PANCE pearls

  • Look for psoriasis in hidden sites — scalp, umbilicus, gluteal cleft, behind the ears — before excluding PsA in a patient with inflammatory arthritis.
  • Dactylitis and enthesitis are highly characteristic; DIP involvement with nail pitting strongly suggests PsA over RA.
  • Pencil-in-cup deformity is the classic radiographic finding.
  • Systemic steroid tapers can trigger pustular psoriasis flares — avoid when possible.
  • Treat-to-target with regular assessment of joint, skin, and patient-reported outcomes is now standard.

References

  • ACR/NPF 2018 — 2018 ACR/NPF Guideline for the Treatment of Psoriatic Arthritis (Singh et al., Arthritis Rheumatol 2019)
  • GRAPPA 2021 — GRAPPA Treatment Recommendations for Psoriatic Arthritis (Coates et al., Nat Rev Rheumatol 2022)
  • CASPAR — Classification Criteria for Psoriatic Arthritis (Taylor et al., Arthritis Rheum 2006)

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Commonly confused with

vs Rheumatoid Arthritisvs Osteoarthritis

Related Musculoskeletal diagnoses

Osteoarthritis (OA)Rheumatoid Arthritis (RA)GoutPseudogout (CPPD Disease)Systemic Lupus Erythematosus (SLE)Polymyalgia Rheumatica (PMR)Giant Cell Arteritis (GCA)FibromyalgiaAnkylosing Spondylitis (Axial Spondyloarthritis)Septic ArthritisOsteomyelitisOsteoporosisAcute Low Back Pain and Lumbar RadiculopathyLumbar Spinal Stenosis

Differentials & related conditions

Reactive Arthritis

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