Seronegative Spondyloarthropathies

Psoriatic Arthritis

Definition

Inflammatory arthropathy associated with Psoriasis

Epidemiology

Occurs in 7% of patients with psoriasis
M = F

Classification

Classic

Involvement of DIPJ joints of hands

Deforming
- With Ankylosis & Arthritis Mutilans
RA Like

Similar to RA but without RF

Monoarthritis
Ankylosing Spondylitis Like

Pathology

Joint changes similar to RA
Spine & SIJ changes similar to AS

Clinical Features

Joints
- Usually mild asymptomatic polyarthritis
  - Of IPJ of hands & toes

Condition usually progresses slowly
Severe cases have deformity of hands & feet
- Classically Dactylitis
  - Fusiform swelling of digit
1/3 have Spondylitis & Sacroiliitis

Skin
- Typical skin lesions of Psoriasis
  - Scaling Erythematous Papules
  - On scalp & extensor aspects of limbs (esp elbows & knees)

Usually precedes arthritis

Nails
- 80% have nail changes
  - Cf. 30% with Psoriasis alone

Changes include
- Pitting
- Subungual Keratosis
- Transverse ridging
- General discoloration

Investigations

Laboratory Tests

HLA B27 positive in 60% with sacroiliitis

XR

Changes seen with chronic disease
- Hands
  - Periarticular phalangeal erosions
    - Along phalangeal shaft with scalloping
    - At insertion of ligaments (enesopathy)

Periosteal new bone formation
- Along metacarpal & metatarsal shafts
Distal phalanx
- Whittling of ends of the phalanges
- Tuft resorption
Typical 'Pencil in cup' deformity of DIPJ

Large Joints
- Similar to RA
SIJ
- Indistinguishable from AS
Spine
- Changes similar to AS but tend to be less-defined bamboo appearance
  - Heaped up anterior bone

Tends to develop from cephalad & caudal & advance centrally (cf. AS which tends to arise in TL spine & advance cephalad & caudal)

Differential Diagnosis

Reiter's disease
Gout
Heberden's Osteoarthritis

Differentiating from seronegative RA
- Asymmetrical
- DIPJ involved
- Sacroiliitis

Treatment

Similar to RA