Psoriatic Arthritis and Psoriatic Spondyloarthropathy

Psoriatic arthritis (synonym: psoriatic osteoarthropathy) is an autoimmune response disorder that belongs to the seronegative spondarthropathies. It is strongly associated with dermatologic psoriasis.

Psoriatic spondylarthropathy (synonym: psoriatic spondyloarthritis) refers to the involvement of the axial skeleton in patients who suffer from psoriatic arthritis. A special feature of psoriasis is pustulosis palmoplantaris (PPP) that may be associated with destructive and proliferative changes at the anterior chest wall (sternocostoclavicular hyperostosis), spine, and appendicular skeleton (PEO, pustulotic enthesio-osteitis; or PAO, pustulotic arthro-osteitis; or SAPHO—synovitis, acne, pustolosis, hyperostosis, osteitis). Actually we prefer the acronym PEO, because it best describes the essential features of the disease.

Etiology

The etiology of all clinical manifestations of psoriasis, psoriatic arthritis, and psoriatic spondylarthropathy seems to be a T-cell–dependent and tumor necrosis factor–mediated, multifactorial (genetic, environmental) autoimmune disorder.

Prevalence and Epidemiology

Psoriasis has no known sex predilection. Its peak incidence is between 30 and 50 years of age. It has been estimated that between 2% and 4% of the population in Western countries have some clinical degree of psoriasis vulgaris. Up to 15% of these patients develop clinically and radiographically variable degrees of a generalized enthesitis including psoriatic arthritis and spondyloarthritis, periostitis, and tendonitis. Psoriatic spondyloarthritis accounts for almost 20% of the seronegative spondylarthropathies. A genetic association via the HLA-B27 antigen has been identified. Among HIV-infected patients, psoriatic arthropathy is 40 times more likely than in the normal population.

Clinical Presentation

Psoriasis principally is a systemic disease with a high rate of comorbidity (hypertension, coronary heart disease, etc.). Dermatologic changes include erythematous macules with a silvery-white scale ( Fig. 49-1 ); nail changes (oil spots, pitting, crumbling) ( Fig. 49-2 ); and pseudosterile pustules ( eFigs. 49-1 and 49-2 ). The changes can be very subtle: For instance, on the head. PPP ( eFig. 49-3 )—an inverse form of psoriasis—often is misdiagnosed as dyshydrotic eczema or fungal infection. PPP is observed in smokers more often than in nonsmokers.

FIGURE 49–1, Typical periosteal ossification at the proximal aspects of the left tibia and fibula ( A and B ), where this 34-year-old patient had complaints of swelling and erythema. CT ( C ) suggests that the periosteal changes predominate and are not the result of a process in the marrow space. Inspection of the patient's skin revealed a typical psoriatic lesion on the right lower leg ( D ).

FIGURE 49–2, Psoriatic spondyloarthritis in the mid-thoracic spine. MR imaging signs of spondylodiskitis and spondylitis with edema-like increased T2 signal are present in the involved vertebral bodies ( A ) with simultaneous erosions and sclerosis as well as syndesmophytes on CT ( B and C ). Note the paravertebral soft tissue swelling. In ( D ) there are classic signs of psoriasis at the great toe.

eFIGURE 49–1, A 39-year-old woman with severe anterior chest wall disease and pustulosis palmoplantaris (PPP). Massive swelling at the anterior chest wall ( A ) was interpreted as Tietze syndrome. Plantar ( B ) and palmar PPP ( J ) was present. Active sternocostoclavicular hyperostosis was noted with destruction and new bone formation; note massive soft tissue swelling, especially behind the manubrium ( C-E ). The patient also suffered from low back pain. A radiograph of the lumbar spine ( F ) revealed a “white” third vertebral body with classic syndesmophytes at the corners. A bone scan ( G-I ) shows the bullhead sign ( G ) and increased tracer uptake in the third vertebral body ( H , I ), indicating that both skeletal manifestations of pustulotic enthesio-osteitis were active.

eFIGURE 49–2, Late stage of sternocostoclavicular hyperostosis with platelike enthesitic ossification ( A-C ). In the same patient a bone scan shows the bullhead sign ( D ); a picture of his palmar pustulosis palmoplantaris ( E ).

eFIGURE 49–3, A 64-year-old patient with back and anterior chest wall pain for several years. The radiologic changes were interpreted as multifocal chronic infectious osteomyelitis, according to a histologic report of a biopsy from the fifth lumbar vertebral body. The patient was treated with antibiotic drugs repeatedly, but there was no change. Inspection of the patient's hands and feet revealed classic pustulosis palmoplantaris, which had been treated in the past with antimycotic ointment but without any improvement. On these three reformatted CT images ( A-C ), all changes that are pathognomonic for the diagnosis pustulotic enthesio-osteitis (PEO, or SAPHO [synovitis, acne, pustolosis, hyperostosis, osteitis]) are documented: spondylitis and spondylodiskitis with syndesmophytes at C6, T7-9, L3, and L5, destructive and osteoproliferative changes in the manubrium, and synchondrosis manubriosternalis.

Clinical symptoms derive from inflammatory changes at the entheses of joints with secondary synovitis, of bones of the axial and appendicular skeleton and of tendons (e.g., the Achilles tendon). Patients may present with diffuse swelling of one or more digits (dactylitis). In the case of PPP, pain and swelling of the anterior chest wall are the dominating symptom.

According to the literature, in 20% to 30% of cases no psoriatic skin changes are present at the beginning of arthritic changes. However, we believe that this rate is too high, because many patients are not investigated by experienced dermatologists. After a sudden onset (pseudogouty arthritis), the course of the disease usually is in waves. Rarely, the course of the disease is primarily chronic. In our experience, in many patients, especially with PEO (SAPHO), clinical and radiologic symptoms will be misdiagnosed by the various involved specialties (dermatology, radiology, orthopedics, rheumatology, general medicine), and patients go through a long odyssey before a correct diagnosis is made.

Pathophysiology

The current concept of spondyloarthritides is based on the assumption of a generalized enthesitis. To entheses belong all transitions between soft tissue and bone, including periosteum, tendon insertions, joint capsules, discovertebral junctions, synchondroses, and syndesmoses.

Entheses often have a very sophisticated anatomy and usually are exposed to stress. It is their task to reduce mechanical stress on the bony structures beyond the enthesis. In the case of a tendon insertion, a complex fibrocartilage buffer reduces the strength of mechanical force. A special feature of these inflammatory changes is that inflammatory destruction and repair with reactive new bone formation takes place simultaneously and not metachronously as in bacterial processes. In contrast to rheumatoid arthritis, inflammation of the joints in psoriatic arthritis is considered to be a secondary synovitis following an enthesitic capsulitis.

Imaging Techniques

Techniques and Relevant Aspects

Early Changes

It is very important to detect early changes, because only in the early stages of disease are therapeutic strategies relevant.
Psoriatic arthritis: Early changes may best be detected with MRI using T2-weighted sequences. According to the pathomechanism, they present with increased signal at the various entheses of the hands and feet—that is, at the capsular insertions of the distal and proximal interphalangeal (DIP and PIP) joints and at their various ligament insertions. Increased T2 signal in the underlying bone is the result of osteitis. Early bony destruction presents as marginal erosions. Reactive new bone formation at the base of erosions is best visualized by radiographs or CT.
Periostitis: Early changes present with increased T2 signal in subperiosteal bony structures (osteitis), but early periosteal new bone formation with thickening of the cortex is best visualized by CT.
Spondyloarthritis: In early stages, targets of inflammatory attacks are the corners of the vertebral bodies (discovertebral junctions) and the end plates with development of spondylodiskitis, also called an inflammatory Anderson lesion. T2-weighted MR images reveal high signal at these sites. CT images present with the typical mixture of bony destruction and repair, which in our experience occurs in nearly all cases at the same time as early findings on MRI.
Sacroiliitis: Sacroiliitis can be observed in about 50% of patients with psoriatic skeletal changes, especially in combination with spondyloarthritis. In early cases, synovitis and subchondral bone marrow inflammation (osteitis) are the most important MR features, but early bony repair and bony bridges are better visualized by CT.
Anterior chest wall disease in patients with PPP and pustulotic psoriasis: In early stages, edema-like increased T2 signal and soft tissue swelling around the sternocostoclavicular region can be visualized on MRI, but usually coincident bony destruction and new bone formation are better demonstrated with CT.

Late Changes

Bone changes in late stages of psoriatic arthritis, spondyloarthritis, tendonitis, periostitis and anterior chest wall disease are typical and diagnostic in most cases. They are sufficiently visualized on radiographs and CT

Pros and Cons

In most patients with a long history of pain and swelling of joints, especially the hand joints, and with obvious skin changes, radiographic exams are sufficient ( Figs. 49-3 and 49-4 ). In psoriatic patients with back pain and equivocal changes in the spine on radiographs, CT is indicated (see Fig. 49-2 ). In patients with a short history (<3 months), however, MRI is the indicated study. MRI is also useful for monitoring therapeutic response. It can also assist in differentiating psoriatic arthritis and rheumatoid arthritis. This statement is based on differing sites of edema-like changes (see later). Scintigraphic bone scans may help demonstrate the pattern of distribution of early enthesitic changes that indicate musculoskeletal involvement. The role of scintigraphic bone scans as well as PET-CT in monitoring patients under therapy (therapeutic response) has not been sufficiently investigated.

FIGURE 49–3, Transverse pattern of psoriatic arthritis at the hands and feet ( A and C ). Note the mixture of fine erosions and bone proliferation (protuberances) at the bases of the distal phalanges and the typical spiculated bone proliferation where the dorsal finger tendons insert. The bone scan ( B ) reflects the distribution of inflammatory changes.

FIGURE 49–4, Clinical “sausage” digit of the right ring finger of a patient with a family history of psoriasis ( A ). Note slight periarticular osteoporosis of the distal and middle phalanx with subtle periosteal ossification at the middle phalanx as well as delicate protuberances at the base of the distal phalanx. These signs are suspicious for but not proof of the axial type of psoriatic arthritis. However, a complementary radiograph of the asymptomatic foot ( B ) reveals classic signs of psoriatic polyarthritis, especially at the great toes.

Manifestations of the Disease

Peripheral Skeleton

General

Initial joint complaints are usually mono- or oligoarticular. Typical manifestations of skeletal disease are enthesitic capsulitis and secondary arthritis, especially involving the articulations of the hands and feet. A certain predilection for the great toe has been noted. Large joints are involved in fewer than 10% of cases.

In later stages the distribution changes to being oligo- or polyarticular. Polyarticular disease is characterized by the distribution among the small joints of the fingers and toes: transverse (DIP and/or PIP joints), axial (one or more fingers or toes), and symmetric or asymmetric.

The findings at the insertions of tendons (i.e., calcanei, trochanters, ischial tuberosities) are relatively specific—as in other seronegative spondyloarthropathies—with destruction and simultaneous polymorphic (i.e., spiculated) ossification and accompanying bursitis.

Massive swelling of the extra-articular soft tissues of a digit is termed psoriatic dactylitis. The affected fingers or toes have a sausage-shaped appearance (sausage digits).

Radiographic

According to Freyschmidt, survey examinations should include radiographs of both hands and feet, the lower thoracic spine, the lumbar spine, and other symptomatic regions or joints in two projections.

Relatively early changes that can be visualized are:

Erosions and/or osteoproliferation with spiculated or wooly sites at the bases of the distal phalanges (also called protuberances), sometimes visible only at high image magnification.
Acro-osteolysis (at the insertion of extensor tendons)
Layered periostitic ossification on the shafts of tubular bones.

Later signs in the appendicular skeleton are:

Nondelineation of the subchondral plate,
Increasing marginal joint and central erosion and destruction, in most cases associated with reactive new bone formation (see Fig. 49-3 ; eFig. 49-4 )
Increasing protuberances (see Figs. 49-3C and 49-4B )
Periosteal new bone formation with thickening of the involved long bone (see Fig. 49-1 )
Joint space narrowing
Ankylosis
Frank joint destruction (arthritis mutilans)

eFIGURE 49–4, Late stage of psoriatic spondyloarthritis in the dorsal and lumbar spine with advanced ankylosis caused by syndesmophytes and ossification of the long anterior intervertebral ligament in this 52-year-old patient ( A-D ). There is no involvement of the sacroiliac joints.

As for distribution, most often the DIP joints of the hands and feet are involved symmetrically. The distribution of the visible changes is of key importance in the radiographic assessment and classification of the disease. If all the joints of one finger or toe are involved, the pattern of involvement is called “axial” or “vertical” (see Fig. 49-4A ). If all the DIP joints of a hand or foot are affected, a “transverse” or “horizontal” pattern (see Fig. 49-3A ) is present. Axial and transverse involvements tend to occur asymmetrically; there are also asymmetric mixed patterns.

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here