You are in: eMedicine Specialties > Radiology > MUSCULOSKELETAL Psoriatic ArthritisArticle Last Updated: Apr 13, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 11
  Author: Noah S Scheinfeld, MD, JD, FAAD, Assistant Professor, Department of Dermatology, Columbia University; Consulting Staff, Department of Dermatology, New York Medical College-Metropolitan Hospital; Private Practice Noah S Scheinfeld is a member of the following medical societies: American Academy of Dermatology Coauthor(s): Ann M Johnson, MD, Pediatric Radiology Fellow, Department of Radiology, The Children's Hospital of Philadelphia; Christopher G Filippi, MD, Assistant Professor, Department of Radiology, Division of Neuroradiology, New York Presbyterian Hospital, Weill Medical College of Cornell University Editors: Amilcare Gentili, MD, Clinical Professor of Radiology, University of California at San Diego; Consulting Staff, Department of Radiology, Thornton Hospital; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Lynne S Steinbach, MD, Chief of Musculoskeletal Radiology, Professor, Department of Radiology, University of California at San Francisco; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Felix S Chew, MD, EdM, MBA, Professor, Department of Radiology, Section Head of Musculoskeletal Radiology, Vice Chairman for Radiology Informatics, University of Washington Author and Editor Disclosure Synonyms and related keywords: PA, psoriasis, psoriatic arthritis mutilans, arthritis mutilans, asymmetric oligoarthritis, asymmetric arthritis, symmetrical polyarthritis, psoriatic spondylitis, seronegative spondyloarthropathy, rheumatoid arthritis, RA, PPP, palmaris et plantaris, palmoplantar pustulosis, pustulotic arthro-osteitis, pustulotic arthrosteitis, PAO INTRODUCTIONSection 2 of 11
  BackgroundAccording to the National Psoriasis Foundation's 2001 Benchmark Survey,1 psoriatic arthritis (PA) is a specific type of arthritis that has been diagnosed in approximately 23% of those who have psoriasis. PA can begin in any age group; however, in most patients, it manifests from age 30-50 years. On average, this condition appears about 10 years after the first signs of psoriasis occur, but in about 1 of 7 people with PA, arthritis symptoms occur before any skin lesions appear. Most patients with PA also have psoriasis; patients rarely have PA without psoriasis. Five types of PA have been defined that can coexist but tend to occur separately in most cases:
Classic, but not wholly pathognomonic, associations of PA include the following:
A haplotype epidemiologic association with PA involves the expression of both class I and class II human leukocyte antigen (HLA) alleles, including HLA-B13, HLA-B17, HLA-B27, HLA-B38, HLA-B39, HLA-Cw6, HLA-DR4, and HLA-DR7. HLA-27 is present in 60% of individuals with the disease, as compared with 8% of the general population. Factors that portend a worse prognosis for PA include the following:
Systemic involvement can occur with ocular changes (30%), conjunctivitis, episcleritis, and keratoconjunctivitis sicca. Aortic valve disease has also been described. Because of the high skin turnover, hyperuricemia and gout can occur, coinciding with the psoriasis. An association with human immunodeficiency virus (HIV) infection is also identified; in such cases, both the psoriatic eruption and psoriatic arthritis can be severe. Celiac disease is also reported. For excellent patient education resources, visit eMedicine's Psoriasis Center. Also, see eMedicine's patient education articles Types of Psoriasis, Psoriatic Arthritis, and Understanding Psoriasis Medications. PathophysiologyGenetic, environmental, and immune factors play a role in the pathophysiology of PA. PA belongs to the disease group known as seronegative spondyloarthropathies, and the proximate cause of PA is activated macrophages that release enzymes and chemicals into the joint space to destroy bone, tendons, and cartilage. Approximately 40% of people who develop PA have a family member with either psoriasis or arthritis. FrequencyUnited StatesPA affects at least 5-25% of the 3-6 million people (1-3% of the population) with psoriasis in the United States. InternationalLike psoriasis, PA is more common in countries situated in northern latitudes. Mortality/MorbidityMorbidity is minimal in the mild forms of asymmetrical small-joint oligoarthritis; however, the severe form of arthritis mutilans can result in the loss of fingers. RacePA is more common in whites than in blacks. SexMen and women are equally affected. AgeThe average age at onset of PA is 30-50 years, but the disease can start at any time in patients with psoriasis. AnatomyThe process of PA most commonly involves the small joints of the hands and feet, especially the distal interphalangeal (DIP) joints. At times, the spine is involved as well. Clinical DetailsPsoriasis is mostly a disease of the skin wherein some stimulus leads to a hyperproliferation of skin cells, which then results in an increased turnover of such cells. Patients develop papules and plaques with micalike scales; such plaques have a predilection for the sacrum, elbows, and scalp. PA can lead to joint swelling and, in the most severe case, sausagelike digits. Synovitis can manifest as edema, joint effusion, or tendinitis. Preferred ExaminationPA is diagnosed and assessed with radiography, which is the cornerstone in assessing and monitoring inflammatory arthritides such as PA. Radiographic findings are reproducible and allow for the serial monitoring of patients. Although magnetic resonance imaging (MRI) is more sensitive, the cost of this modality makes it a second-line means for monitoring patients with PA. Limitations of TechniquesIn some cases, it is hard to distinguish PA from other types of arthritis, such as RA. PA is often asymmetrical, whereas RA is not. DIFFERENTIALSSection 3 of 11
[Reiter Syndrome, Musculoskeletal] Ankylosing Spondylitis Rheumatoid Arthritis, Hands Rheumatoid Arthritis, Spine Other Problems to Be ConsideredEnteropathic arthritis (arthritis of inflammatory bowel disease) RADIOGRAPHSection 4 of 11
FindingsPlain radiography is the main imaging modality for assessing PA, although early PA may have no radiographic findings. Soft-tissue swelling often precedes osseous findings. Radiologic findings of PA, with distinctions from other conditions, are as follows: Fingers Fournie et al prospectively compared power Doppler ultrasound findings in 25 fingers that had RA with findings in 25 fingers that had PA.2 Both RA and PA patients had erosive synovitis and tenosynovitis. PA extrasynovial changes occurred in 21 of 25 patients (84%), whereas no patients with RA had extrasynovial changes. Of the 21 patients with PA who had fingers showing extrasynovial changes, 60% of them also had synovial changes. The extrasynovial changes in patients with PA reflected the following:
The main patterns of the extrasynovial changes were the following:
Pseudotenosynovitis, which is marked by diffuse inflammation of the digital soft tissues, occurred rarely. Hands and feet
Spine
Sacroiliac joints
Other sites
The radiographic appearance of PA can be similar to that of RA. The distinguishing features of PA include the following:
A pattern of predominant DIP involvement can also distinguish PA from RA. In the axial skeleton, cervical spinal involvement can be prominent in RA, but thoracic and lumbar changes are unusual. Sacroiliac involvement is a minor feature of RA, but large joints are more involved in RA than in PA. The distinction between PA and other seronegative spondyloarthropathies is largely based on distribution. PA involves both the upper and lower extremities, whereas Reiter syndrome predominantly involves the lower extremities. Ankylosing spondylitis causes changes mainly in the axial skeleton, with bilateral and symmetrical changes being the rule. The spinal bony excrescences of PA and Reiter syndrome are larger and broader than the typical thin, linear syndesmophytes of ankylosing spondylitis. An entity often grouped with psoriasis is pustulosis palmaris et plantaris, or PPP. In 1996, Mejjad et al reported that palmaris et plantaris and PA can be distinguished by their radiologic findings. The anterior chest wall, especially the sternocostoclavicular joints, is more frequently involved in pustulotic arthritis than in psoriasis, both clinically and radiologically. Sternocostoclavicular joints generally appear with erosive lesions in psoriasis but with large ossifications in palmaris et plantaris. Peripheral joint involvement is monoarticular or oligoarticular and affects the proximal joints in palmaris et plantaris (74% vs 21%), or it may be polyarticular and involve small distal joints in psoriasis (60% vs 0%).5 In PA, peripheral joint involvement is more often erosive (43% vs 8%). The frequency rates of sacroiliitis and spinal involvement are similar in palmaris et plantaris and psoriasis. Biologic features and bone scans do not help in distinguishing these 2 conditions. Achilles tendon
Degree of ConfidenceDifferentiating PA from RA can be difficult; however, the following may aid in the diagnostic effort:
The Fournie et al study2 is promising in that it will help distinguish PA from RA. False Positives/NegativesNormal variants do not commonly mimic PA, but other types of inflammatory arthritis can. CT SCANSection 5 of 11
FindingsAlthough plain radiography is the primary modality in assessing PA, computed tomography (CT) scan studies can provide further information about the extent and severity of disease. This is particularly true in areas that are difficult to evaluate with radiographs, which include the sacroiliac joint, the temporomandibular joint, and the sternum/manubrium. In particular, CT scanning is useful in identifying inflammatory lesions, even when preexisting degenerative disease is present; in demonstrating the articular surfaces of bone in an exact fashion; and, in some cases of sacroiliitis, in clearly demonstrating erosive changes that can appear equivocal or negative with radiography. Furthermore, CT scans can demonstrate a variety of findings in PA, including right sternal bone sclerosis with surrounding subchondral erosion and a clavicular bone sclerosis, and can show bilateral clavicular osteophytes and discrete surrounding subchondral cysts and erosions. Degree of ConfidenceCT scanning is not the most sensitive or most specific test for assessing PA, but this modality is useful in the identification of inflammatory lesions, even when preexisting degenerative disease is present. CT scanning is also useful in assessing the extent and nature of the erosive process that is at the heart of PA. False Positives/NegativesCT scanning is not helpful in distinguishing PA from the diseases that mimic this condition. However, once a diagnosis is established, CT scanning is useful in assessing disease extent and nature. MRISection 6 of 11
FindingsFindings on magnetic resonance imaging (MRI) are the most sensitive and specific for sacroiliitis and for other changes in the axial skeleton and in the hands and feet. With MRI, it is possible to identify the early inflammatory phase of enthesitis before the development of erosion, as seen on radiographs. MRI can depict early cortical erosion, inflammatory granulation tissue, and bone marrow edema. In patients with PA, MRIs of the temporomandibular joint can show slight anterior displacement of the disk as well as large condylar erosions and joint effusion, without or with the use of contrast agent. In 2001, Morrison et al summarized psoriatic findings in the ankle and foot.7 The sausage digit is a typical clinical finding in PA and can be seen as diffuse soft-tissue edema of the digits. On MRIs, tenosynovitis with increased fluid in the tendon sheath and enhancement related to synovial proliferation can be seen. The terminal tuft can show edema and enhancement with psoriatic involvement of the nail bed. The bursae can demonstrate fluid and enhancing synovial tissue; this is true for the anatomic bursae—in particular, the retrocalcaneal bursa and the adventitial bursa—as a result of friction. Enthesis inflammation manifests as plantar fasciitis, with edema and enhancement of the proximal plantar fascia and the adjacent calcaneus. Reactive edema in the adjacent tissue beneath the tendon is linked to involvement of the tendon sheath. Effusions and synovial proliferation can be seen as a result of joint involvement. Synovial proliferation within joints is seen as "dirty fluid" on T2-weighted images. Inflamed synovial tissue is strongly enhancing on gadolinium-enhanced images. Chronic synovial proliferation can demonstrate a high T1 signal, representing hyperplasia of subsynovial fibrofatty connective tissue without a pannus. Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of theeyes;jointstiffnesswithtrouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape. Thickened nails with low signal intensity on T1-weighted MRIs are typical findings of nail involvement. MRI can show the underlying histopathologic changes of edematous and/or fibrotic synovial tissue, which can cause erosions of cortical bone and eventually lead to complete destruction of the joint. In 1998, Offidani et al found 68% of patients with PA had positive findings with at least 1 arthritic sign on MRIs, whereas only 32% of the same patients had positive findings with the standard x-ray procedure.8 Abnormal signal intensity in the subchondral focal areas was seen in 9 patients but in none of the control subjects. A high percentage of psoriatic patients without apparent arthritic signs and symptoms had hand articular involvement, particularly distention of the capsule and periarticular edema on MRIs.
The results of McQueen et al's OMERACT MRI scoring system demonstrated the following:
Degree of ConfidenceIt can be hard to distinguish PA from diseases such as RA; in cases where enthesitis is present, this differentiation is less difficult. MRI is one part of the process in diagnosing PA; testing for RF and physical examination for the presence of the lesions of psoriasis are also useful. False Positives/NegativesWith MRI, normal variants should not mimic disease. Infectious arthritis caused by Staphylococcus aureus and Mycobacterium tuberculosis tends to have a more rapid course and a clinical picture not consistent with that of PA. ULTRASOUNDSection 7 of 11
FindingsIn PA, joint effusion and synovitis result in hypoechoic sonograms. In most cases, the joint space is widened and appears hypoechoic; in some cases, a pseudocystic image connected with the joint space can be observed. Increased thickness of the joint capsule can also be present, and the joint capsule is usually clearly distinct from the condylar head, which appears as a linear hyperechoic line with posterior shadowing. Today, ultrasonography is considered a highly specific technique, not only for demonstrating soft-tissue alterations but also for visualizing bone abnormalities, especially in the examination of the small joints. Thus, alterations of the condyle are observed more frequently with ultrasonography than with MRI. The ultrasonographic features of dactylitis in PA have been investigated, and flexor tenosynovitis was detected in more than 90% of the tested patients.11 Dactylitis and articular synovitis were associated in more than 50% of patients. Degree of ConfidenceUltrasonography is useful for assessing the extent of disease, but it is not the method of choice for monitoring bone involvement in PA.12 False Positives/NegativesNormal variants should not mimic the findings of PA; however, other inflammatory types of arthritis can do so. NUCLEAR MEDICINESection 8 of 11
FindingsBone scanning is a useful technique for assessing the inflammatory nature and extent of PA. Whole-body scintigraphy shows the distribution of active joint disease. Abnormal radiotracer uptake precedes findings on plain radiographs. Enthesopathies can be readily detected on bone scans and show hyperactive foci. This is the case when technetium-99m (99mTc) bisphosphonate bone scans are centered on the chest wall, where the jugular notch, costal notches, and xiphoid are most commonly involved. Enthesopathy manifests with a radiologic triad: hyperostosis, osteitis, and periostitis syndrome. Bone scans are also useful for assessing palmaris et plantaris and a related condition, pustulotic arthrosteitis, or PAO. The bone scan can show characteristic, bullheadlike, high tracer uptake in the sternocostoclavicular region; in the bullhead sign, the manubrium sterni represents the upper skull, and the inflamed sternoclavicular joints correspond to the horns.13 Degree of ConfidenceBone scanning is highly sensitive but not specific; bone scans may show that inflammation exists, but a positive finding is not diagnostic of PA and must be correlated to clinical findings. False Positives/NegativesOther types of inflammatory arthritis, as well as infection and trauma, can sometimes mimic PA when a bone scan is used. 99mTc phosphate scans show the location and distribution of active lesions. Scintigraphy enables the inexpensive and simple assessment of joints in the body, but the anatomic detail is poor and the specificity is low. INTERVENTIONSection 9 of 11
In a phase IV, 24-week, multicenter, open-label study of etanercept, Kimball et al demonstrated reductions in healthcare resource utilization in patients with active PA who received etanercept therapy.14 Medical/Legal Pitfalls
MULTIMEDIASection 10 of 11
REFERENCESSection 11 of 11
Article Last Updated: Apr 13, 2007 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
