Msk Dermatology · Year 2 · from Msk Dermatology

Case 3: Psoriasis with Psoriatic Arthritis

Patient Presentation

Demographics: 42-year-old male

Chief Complaint: Scaly skin plaques and new joint pain

History of Present Illness: The patient has had psoriasis since his late 20s, primarily controlled with topical corticosteroids. Over the past 6 months, he has developed pain and swelling in multiple finger joints and his right knee. He reports morning stiffness lasting over an hour. He also noticed his fingernails have become pitted and are separating from the nail bed.

Past Medical History:

  • Psoriasis vulgaris (plaque psoriasis) x 15 years
  • Obesity (BMI 32)
  • Hyperlipidemia

Physical Examination:

  • Skin:
  • Well-demarcated erythematous plaques with silvery scale
  • Distribution: Elbows, knees, scalp, lower back
  • Koebner phenomenon (plaques at sites of old scars)
  • Auspitz sign present (pinpoint bleeding with scale removal)
  • Nails: Pitting, onycholysis, oil spots
  • Joints:
  • Dactylitis of right third finger ("sausage digit")
  • DIP joint swelling and tenderness
  • Right knee effusion
  • Enthesitis at Achilles insertion

Workup and Results

Laboratory Studies:

  • ESR: 42 mm/hr (elevated)
  • CRP: 2.8 mg/dL (elevated)
  • RF: Negative
  • Anti-CCP: Negative
  • HLA-B27: Positive

X-rays:

  • Hands: Erosive changes at DIP joints
  • "Pencil-in-cup" deformity of distal phalanx

Skin Biopsy (prior):

  • Parakeratosis, acanthosis, elongated rete ridges
  • Munro microabscesses

Clinical Image

Clinical photograph demonstrating classic plaque psoriasis with well-demarcated erythematous plaques covered by thick silvery scale on the elbow, a common location for psoriatic lesions.

Diagnosis

Psoriasis Vulgaris with Psoriatic Arthritis

Features:

  • Classic plaque psoriasis (80-90% of psoriasis cases)
  • Psoriatic arthritis with DIP predominant pattern, dactylitis, and enthesitis
  • Nail involvement (pitting, onycholysis)

Discussion

This case illustrates psoriasis and psoriatic arthritis:

  • Th17/IL-17 Pathway: The lecture identifies the IL-17 pathway as central to psoriasis pathogenesis. Th17 cells and IL-17/IL-23 drive keratinocyte hyperproliferation.
  • Accelerated Turnover: The lecture notes that keratinocyte turnover is accelerated to 3-5 days (normal is 28 days), causing the characteristic thick scale.
  • Auspitz Sign: The lecture describes pinpoint bleeding when scale is removed (Auspitz sign) as characteristic of psoriasis.
  • Psoriatic Arthritis: The lecture states that approximately 30% of psoriasis patients develop psoriatic arthritis. Dactylitis ("sausage digit") is highly characteristic.
  • Nail Findings: The lecture identifies nail pitting as characteristic of psoriasis.

Treatment Plan

  1. For Joint Disease (Primary Concern):
  • TNF-alpha inhibitor OR IL-17 inhibitor (secukinumab, ixekizumab)
  • Treats both skin and joints
  • NSAIDs for symptom relief
  1. For Skin Disease:
  • Biologic therapy (same agent treats both)
  • Topical therapy for localized plaques (adjunct)
  • Narrowband UVB phototherapy if needed
  1. Comorbidity Management:
  • Cardiovascular risk assessment (psoriasis increases CV risk)
  • Weight management (obesity worsens psoriasis)
  • Lipid management
  1. Monitoring:
  • Joint exams every 3-6 months
  • PASI score for skin disease
  • Screen for TB before biologics

Teaching Points

  1. IL-17 and IL-23 are key cytokines in psoriasis (Th17 pathway)
  2. Keratinocyte turnover accelerates to 3-5 days (normal 28 days)
  3. Auspitz sign = pinpoint bleeding with scale removal
  4. ~30% of psoriasis patients develop psoriatic arthritis
  5. Dactylitis and nail pitting are characteristic findings

Image Reference

For visual reference of common dermatologic conditions, see:

Learning Points

  1. Acne Pathogenesis: Four factors - sebum, hyperkeratinization, C. acnes, inflammation; isotretinoin addresses all
  1. Isotretinoin Requirements: iPLEDGE mandatory; monitor pregnancy tests, LFTs, lipids
  1. Atopic Dermatitis Features: Atopic triad; filaggrin mutations; IL-4/IL-13 targeted by dupilumab
  1. Eczema Herpeticum: Emergency requiring IV acyclovir
  1. Psoriasis/PsA: IL-17 pathway; 30% develop arthritis; dactylitis and nail pitting characteristic

All cases for this lecture as Markdown