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Prominent features in psoriatic arthritis are synovitis, enthesitis, erosions and
new bone formation. Biopsies of the joint tissue revealed increased white blood
cells and prominent blood vessels, and 47 % patients develop erosions in bones
within 2 years of diagnosis [
53
]. Enthesitis and bone marrow edema on MRI
demonstrate its similarity with other seronegative spondyloarthritis.
Psoriatic arthritis develops in 4
30 % patients with psoriasis [
52
,
54
], with a
-
prevalence of 0.1
0.2 % of the general population [
54
]. It affects men and women
equally, most commonly developing in people aged 30
-
55 years.
-
3.2.2 Clinical Manifestations
Five clinical patterns have been described in psoriatic arthritis: asymmetric olig-
oarthritis, symmetric polyarthritis, distal interphalangeal (DIP) arthropathy, arthritis
mutilans, and spondylitis with or without sacroiliitis [
55
]. Patients may have fea-
tures of more than one pattern, and their presentations may change during the
course of the disease.
Asymmetric oligoarthritis is the most common pattern, and involves in
am-
mation in fewer than 5 joints. Large joints, such as knees or hips, are affected most
often. The symmetric polyarticular pattern resembles rheumatoid arthritis, and
mainly involves small joints such as fingers, hands and wrists. DIP arthropathy,
affecting the
fl
finger joints closest to the nails, is a characteristic of psoriatic arthritis,
being rarely seen in rheumatoid arthritis. Patients with peripheral joint involvement
often complain pain and swelling of these joints, associated with morning stiffness.
Synovitis, or in
ammation of lining of the joint, is the underlying pathology.
Arthritis mutilans is a rare destructive condition caused by absorption of the
fl
nger
bones, and is also characteristic of psoriatic arthritis.
Spine involvement is less common than limb arthritis in psoriatic arthritis. Back
pain, buttock pain, stiffness, and fatigue are the main complaints in these patients.
Involvement of the sacroiliac joints is not always present in psoriatic arthritis, or
may only affect the right or left side, as opposed to both sacroiliac joints in AS.
Another commonly affected site is the cervical spine. As seen in rheumatoid
arthritis, in
fl
ammation and erosions can cause atlantoaxial (C1
C2) subluxation,
-
which can lead to cervical myelopathy.
Enthesitis is often present in patients with psoriatic arthritis. Patients may report
pain and sometimes swelling at the heel or the bottom of the foot. A few features
help to distinguish psoriatic arthritis from AS. Psoriatic skin and nail changes are
seen in most patients, providing the major diagnostic clue. Sausage-shaped swelling
of a
finger or toe is a characteristic manifestation of psoriatic arthritis [
56
]. Ultra-
sound and MRI studies show that in
fl
ammation of the tendon sheath (tenosynovitis)
is the cause of this type of
finger or toe swelling.
Laboratory tests are non-diagnostic. Elevated blood markers of in
ammation
may be present [
57
]. As one of the seronegative spondyloarthritis, rheumatoid
factor and anti-CCP antibody are often absent. HLA-B27 is present
fl
in some
