Psoriatic Arthritis (PSA) - An Analysis of 220 Patients

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1 Quarterly Journal of Medicine, New Series 62, No. 238, pp , February 198 Psoriatic Arthritis (PSA) - An Analysis of 22 Patients D. D. GLADMAN, R. SHUCKETT, M. L. RUSSELL, J. C. THORNE, and R. K. SCHACHTER From the University of Toronto Rheumatic Disease Unit, Women's College Hospital, and the Psoriasis Education and Research Center, Women's College Hospital, Toronto, Ontario Accepted 11 September 1986 SUMMARY Since 198,22 patients with psoriatic arthritis have undergone detailed study at the Women's College Hospital In Toronto, Canada. Clinical, radiological and biochemical data were subjected to computer analysis in order to determine clinical-biochemical correlations within subsets of patients with psoriatic arthritis. Our findings indicate a spectrum of disease patterns and severity. Overall, we found a 4 per cent incidence of deforming, erosive arthropathy, with 1 per cent of patients having five or more deformed joints. ARA stage 3 and 4 radiological joint change occurred in 28 and 14 per cent respectively, and 11 per cent of patients had ARA Class HI or IV functional impairment. The asymmetric ollgoarthritis previously reported to account for the majority of cases of psoriatic arthritis was not a dominant pattern in our own experience, occurring In only 28 per cent of the series. Polyarthritis was the most common joint pattern, present in 61 per cent with symmetric and asymmetric patterns occurring equally. Our experience suggests that polyarthritis, symmetric or asymmetric, is a more common presentation of the disease than is generally acknowledged. Furthermore, the frequency of deforming destructive arthropathy challenges the concept of psoriatic arthritis as a benign arthropathy. INTRODUCTION The concept of psoriatic arthritis as an entity distinct from rheumatoid arthritis has evolved over the past three to four decades. Epidemiological studies have shown an increased frequency of psoriasis among arthritis patients, and conversely, an increased prevalence of arthritis among patients with psoriasis [ 1]. Clinically, it has been noted that unlike rheumatoid arthritis, there is no female preponderance in the arthritis associated with psoriasis. The description of rheumatoid factor and its association with rheumatoid arthritis further supported the concept that psoriatic arthritis was a separate entity, since it tended to occur in patients who were seronegative. The emergence of the clinical patterns unique to this form of arthritis resulted from the Address correspondence to Dr Dafna D. Oladman, Women's College Hospital, Burton Hall, 6 Grosvenor Street, Suite 423, Toronto, Ontario, M5S IBS, Canada. Supported In part by the Canadian Arthritis Society, and by Women's College Hospital Research Fund. Oxford University Press 198

2 128 D. D. Gladman and others descriptive studies of Wright [2-4] and Moll and Wright [5,6], and the radiological studies of Avila el al. [] and Baker [8]. These were recently summarized by Moll [9]. At present, psoriatic arthritis is defined as an inflammatory arthritis, usually rheumatoid factor negative, associated with psoriasis [6,1]. Moll and Wright described five clinical patterns: (i) arthritis of the distal joints; (ii) arthritis mutilans); (iii) symmetric polyarthritis, indistinguishable from rheumatoid arthritis; (iv) asymmetric oligoarthritis; and (v) spondylo-arthropathy. There have been several studies supporting this concept of psoriatic arthritis and its clinical patterns [1-16]. However, in a number of studies groups were 'lumped' together and the true incidence of each pattern became obscure [11,14,15]. Moreover, in some patients more than one pattern was recognized and it is unclear in what group they were placed. The predominant clinical pattern in the current literature appears to be an asymmetric oligoarthritis, although the exact number of affected joints varies [6, 1-16]. In order to characterize psoriatic arthritis further we have initiated a long-term study of a large group of patients fulfilling its current definition, with a study period of up to six years. This report details clinical, biochemical and radiological findings at the time of initial assessment of the first 22 patients. PATIENTS AND METHODS All patients had an inflammatory arthropathy, associated with psoriasis and most were seronegative. In accordance with recent studies of psoriatic arthritis and the known presence of rheumatoid factor in up to 2 per cent of the general population [15, 1], seropositivity alone was not an exclusion criterion to the diagnosis. However patients with rheumatoid nodules, classical rheumatoid arthritis, crystal-induced arthritis (proven by synovial fluid analysis), grade IV osteoarthritis, Reiter's syndrome and obvious inflammatory bowel disease were excluded. All patients were seen by a rheumatologist at the psoriatic arthritis clinic at Women's College Hospital, a University-based center. The majority of the patients were referred by dermatologists, either directly (4 per cent), or through the Psoriasis Education and Research Center of Women's College Hospital (19 per cent). Other rheumatologists referred 15 per cent, family practitioners 14 per cent, and the remaining 5 per cent were sent to the clinic by other physicians. Patients were evaluated on admission to the study and at six-month intervals thereafter, Assessments included detailed history, physical examination and biochemical and radiological evaluation according to a standard data retrieval protocol, Information was obtained regarding age of onset for both skin and joint disease, pattern of joint disease at onset, relationship between skin and joint manifestations, family history, nail lesions and other extra-articular features including eye disease, cardiac disease and inflammatory bowel symptoms, Inquiry was also made into the presence and duration of morning stiffness, constitutional symptoms, symptoms of inflammatory spinal disease, previous medication, ARA functional level [18] and general medical history. Physical examination consisted of a general medical examination with particular attention to skin, nails, ocular, cardiac and most important, peripheral and axial joints. Both ARA [19] and Lansbury {2] joint counts were used to assess inflammatory activity. The number of deformed joints (ankylosis, subluxation or decreased range of motion attributable to joint damage rather than activity) was recorded. Spinal disease was evaluated by testing for sacro-iliac stress pain, using at least three techniques [21], The Gaenslen's maneuver, performed with the patient supine, with one leg flexed and the other allowed to drop over the edge of the examining table, was considered positive if pain was elicited in the sacroiliac area. The Patrick-FABERE test, performed by applying pressure to the flexed knee, as well as to the opposite anterior superior iliac spine, with the hip in extreme flexion, abduction and external rotation, was considered positive if pain was elicited in the sacro-iliac area.

3 Psoriatic Arthritis (PSA) - An Analysis of 22 Patients 129 Compression and direct palpation of sacro-iliac joints was also carried out. Spinal mobility was assessed by measurement of 1 cm segments [22] and by the finger-to-floor distance for flexionextension. Finger-fibula distances for lateral flexion, direct measurement of thoracic rotation, and cervical spine range of movement were recorded. Radiological evaluation included radiographs of hands, feet, cervical, thoracic, and lumbar spine and sacro-iliac joints. ARA criteria [18] were used to identify the radiological stage of peripheral joints. Sacro-iliac radiographs were graded according to the New York criteria [23]. The presence of both classic and paramarginal syndesmophytes was recorded. The latter were defined as large, bulky ossifications extending between vertebral bodies, usually asymmetrically distributed. Originally described by Bywaters and Dixon [24], they are considered typical of psoriatic arthritis [25]. All radiographs were reported by at least two rheumatologists, without knowledge of patient identity. As a test of inter-observer variation, 4 radiographs were reported without knowledge of patient identity by a third rheumatologist with complete agreement. Based on the clinical and radiological features, patients were classified into one of the following patterns: (i) distal (distal interphalangeal joints only affected); (ii) oligoarthritis (s4 joints); (iii) polyarthritis (2:5 joints); (iv) back (radiological evidence of sacro-iliitis and/or classical syndesmophytes and inflammatory back pain, but without any peripheral joint disease); (v) distal with back; (vi) oligoarthritis with back; (vii) polyarthritis with affected back. Arthritis was divided further into symmetric (identical joints affected on both sides of the body) and asymmetric distribution. Laboratory evaluation included complete blood counts and differential counts and erythrocyte sedimentation rate (ESR) by the Westergren method. Biochemical tests of kidney and liver function, serum uric acid and serum protein electrophoresis were also performed. Serological tests included latex fixation test for rheumatoid factor, fluorescent antibody test for antinuclear antibody (using Hep 2 substrate, titer above 1:4 considered positive), and serum complement levels. All information was entered on an IBM 36 computer. Statistical analysis was carried out using the SAS (Statistical Analysis System) program, and included Student's t test for continuous variables and the^2 test or Fisher's exact test for comparing frequencies between the various patient groups. TABLE 1. Clinical features in 2 patients with psoriatic arthritis Number of females (%) Number of males (%) Mean age at presentation (range) Mean age at onset of skin lesions (range) Mean age at onset of joint disease (range) Duration of psoriasis (range) Duration of psorjatic arthritis Family history of psoriasis/psoriatic arthritis Skin and joints flaring simultaneously Iritis Psoriasis pattern Vulgaris Guttate Nail lesions 116 (53) 14 (4) 46(14-89) 29 (-5) 3 (1-8) 16.6 (-6) 9(-48) 4% 35% % 94% 4% 83%

4 13 D. D. Gladman and others RESULTS General features Among the first 22 patients entered into the psoriatic arthritis clinic there were 116 females and 14 males (female to male ratio of 1.1:1.). Two hundred and seventeen of these patients were Caucasian and three were black. The demographic data of these patients at presentation are outlined in Table 1. There were no significant differences in any of the variables between males and females. Sixty-eight per cent of the patients developed arthritis an average of 12.8 years after the onset of psoriasis; 15 per cent had a simultaneous onset of skin and joint disease (within one year), while in 1 per.cent the arthritis preceded psoriasis by a mean of.4 years (range 1-33 years). Ninety-four per cent of the patients had psoriasis vulgaris at the time of first assessment and 4 per cefft had guttate psoriasis. In 2 per cent of the patients no skin lesions were detected at initial assessment, but they had nail lesions (including nail pits and/or onycholysis) and had had psoriasis vulgaris in the past. Clinical features of psoriatic arthritis On initial visit to the clinic the majority of the patients had evidence of inflammatory joint disease, based on history and physical examination. These features are outlined in Table 2, and in part (a) of Figs Eleven per cent of the patients reported marked restriction of daily activities because of arthritis (ARA functional class III/IV). Indeed, at least one deformity was detected in 43 per cent of the patients, while in 16 per cent, more than five deformed joints were detected, with either significant restriction of movement and/or ankylosis, and/or telescoping of the fingers, the last being classified as arthritis mutilans. Over a quarter of the patients had clinical evidence of either sacro-iliitis or spondylitis. Treatment The majority of patients were treated with non-steroidal anti-inflammatory drugs. However, disease-remittive drugs were used in some patients. Gold was used in 16 per cent of the patients, and it is of note that patients treated with gold were more likely to have evidence of damage, possibly because physicians tended to treat more aggressively those patients with more severe disease. Antimalarials were used in 5 per cent, and azathioprine in 4 per cent of the patients. Weekly methotrexate was used in 24 per cent, and oral corticosteroids by 19 per cent of the patients. Five patients were taking retinoic acid while seven patients were treated with PUVA. TABLE 2. Clinical features of psoriatic arthritis Morning stiffness ARA functional class III/IV Inflammatory neck pain and stiffness Inflammatory back pain and stiffness Actively inflamed joints Deformities 2:1 2:5 Dactylitis Distal interphalangeal joint disease SacToiliac stress pain 52% 11% 23% 18.6% 9% 43% 16% 33% 54% 1%

5 Psoriatic Arthritis (PSA) - An Analysis of 22 Patients 131 FIG. 1. (a) The hands of a patient with asymmetric polyarthritis showing shortening of third left digit, swelling of second left metacarpophalangeal and right fifth metacarpophalangeal joints, (b) The radiographs of the same patient's hands show 'pencil and cup' changes in third left distal interphalangeal, fifth right proximal interphalangeal and erosive changes in several metacarpophangeal joints and both wrists.

6 132 D. D. Gladman and others (a) FIG. 2. (a) The hands of a patient with psoriatic arthritis show significant distal interphalangeal joint disease as well as skin and nail changes. Based on clinical features he might have been included in the distal group, (b) Radiographs of both hands and wrists show significant damage in distal interphalangeal joints, but in addition, erosive changes are noted in several metacarpophalangeal joints as well as in the right wrists, where the ulnar styloid is tapered.

7 Psoriatic Arthritis (PSA) - An Analysis of 22 Patients 133 (a) (b) FIG. 3. (a) The hands of a patient with distal involvement only, (b) Matching radiographs confirming the distal distribution.

8 134 D. D. Gladman and others FIG. 4. (a) Symmetric polyarthritis, rheumatoid arthritis-like, with significant clinical deformity and damage. (b) The radiographs demonstrate that the damage is seen not only in the wrists, metacarpophalangeal and proximal interphalangeal joints but also in the distal interphalangeal joints bilaterally.

9 Psoriatic Arthritis (PSA) - An Analysis of 22 Patients 135 The last four drugs were prescribed primarily for skin disease, and there was no correlation between the severity of the arthritis and their use. We cannot comment on the effect of treatment on the course of the disease at this time. Laboratory features Results of the laboratory investigation are shown in Table 3. Anemia and leukocytosis are commonly associated with psoriasis and psoriatic arthritis. The elevated sedimentation rate noted in almost half of the patients represented both active arthritis and active skin disease. The frequency of positive rheumatoid factor was similar to the incidence of 13 per cent found in a group of 11 patients with psoriasis uncomplicated by arthritis [26], The highest titer of rheumatoid factor (1:64) was seen in a patient with spondylo-arthropathy, and another with distal joint disease and arthritis mutilans; neither had features of rheumatoid arthritis. Antinuclear factor was detected in 1 per cent of the patients, again a frequency similar to that seen in patients with uncomplicated psoriasis [26]. The highest titer of antinuclear factor was 1:16, Hypergammaglobulinemia which was observed in 11 per cent of the patients, was always nonspecifically polyclonal. Radiological manifestations Radiographs revealed erosive disease in 6 per cent of the patients, with stage 4 changes (ankylosis and/or joint destruction) occurring in 3 per cent (Figs. l-4(b)). Sixteen per cent of patients had more than five joints at stage 4. Sacro-iliitis of grade 2 or more was detected in 59 (2 per cent). Eleven per cent of the patients had classic syndesmophytes (Fig. 5 panel a) while 33 patients (15 per cent) had paramarginal syndesmophytes (Fig. 5 panel b). Psoriatic arthritis subsets Grading the pattern of arthritis at onset was based on patient history, and where available, previous records, The assignment of psoriatic arthritis pattern at initial assessment was based on both clinical and radiological findings at the first visit to the clinic. Table 4 compares the frequency of the various patterns at onset to that found at first assessment. Polyarthritis TABLE 3. Laboratory and radiological features in psoriatic arthritis Anemia (Hb<11 females, <125 males) Leukocytosis (WBO1 ) 14% 1% Elevated sedimentation rate (>25 mm/h) Hyperuricemia (>45//mol/l) 41% Females 14% Males 32% Rheumatoid factor (> 1:16) 9% Antinuclear factor (>l:4) 1% Hypergammaglobulinemia (> 16 g/1) 11% Erosive changes on radiographs 6% Stage IV changes (>5 joints) 16% Sacroiliitis (grade 2 or greater) Syndesmophytes 2% Classic Paramarginal 11% 15%

10 116 D. D. Gladman and others c c a ca Q. - O x: a.

11 Psoriatic Arthritis (PSA) - An Analysis of 22 Patients 13 TABLE 4. Psoriatic arthritis pattern in 22 patients Pattern Distal Oligoarthritis Polyarthritis Back alone Back+distal Back-1-oligoarthritis Back+polyarthritis At onset First assessment Total A ' S* * A=asymmetric distribution; S=symmetric distribution (occurring in identical joints in both sides of the body). Figures are percentages. comprised the largest group both at onset and at initial assessment, occurring in more than 4 per cent of the patients. Fewer patients were grouped in the distal and oligoarthritis pattern at initial visit than at onset. This may, however, reflect the patient's inability to remember the type of onset, as in many cases there was a delay in referral to the clinic. More patients in the back+polyarthritis group were found at initial assessment compared with onset. This may represent an actual change in the pattern of arthritis, or, alternatively, it may signify asymptomatic back disease which was only diagnosed after radiological assessment. The patients were divided further into those with symmetric and those with asymmetric distribution. Patients with oligoarthritis with or without back disease, and patients with distal joint disease with an affected back tended to have asymmetric arthritis, while among patients with polyarthritis symmetry and asymmetry were almost equally distributed (Table 4). TABLE 5. Psoriatic arthritis subsets No. of patients F/M Age onset (skin) (years) Age onset (joints) (years) Skin first (%) Joints first (%) Simultaneous onset (%) Family history (%) Simultaneous flares (%) FC m/iv (%) Iritis (%) Nail lesions (%) Sacroiliac pain (%) Back pain (%) Neck and back (%) Distal interphalangeal joints affected (%) Dactylitis (%) Distal 2 9/ / Oligoarthritis Polyarthritis 89 6/ Back disease 5 / Back+ distal 8 3/ Back+ oligo 15 / Back+ poly 45 23/

12 138 D. D. Gladman and others A comparison was carried out among the patients assigned to the seven different patterns of psoriatic arthritis (Table 5). There was a male preponderance only among patients with distal disease and back disease only, while in the other groups, the sex ratio was close to 1. Patients with back disease were older at the time of onset of their arthritis than those without (4 versus 35 years, p=.2), and had a longer disease duration (12 versus 8 years, p=.1). ARA functional class III or IV occurred only in patients with polyarthritis, probably representing the extent of disease. As has been previously noted, dactylitis was more common in patients with distal interphalangeal joint disease (p=.1) than in the other categories. Distal interphalangeal joint disease, however, occurred just as frequently among patients with polyarthritis as it did in the other groups. Grade 4 radiological changes were observed more commonly in patients with distal disease and those with symmetric polyarthritis, suggesting that these forms were more likely to be associated with severe disease. DISCUSSION The concept of psoriatic arthritis as a separate disease, first proposed by Alibert in 1822, received further support by the classic studies of Wright, who established much of the groundwork of our current understanding of the disease. In 1956, Wright described 42 patients with psoriasis and erosive arthritis, and compared them to patients with classical rheumatoid arthritis and patients with psoriasis without joint disease [2]. This study provided evidence that psoriatic arthritis was a specific entity. In contrast to rheumatoid arthritis, psoriatic arthritis occurred as frequently in males as in females, was less often polyarticular at onset, and tended to be less severe than rheumatoid arthritis. In general there were fewer affected joints, fewer deformities such as ulnar deviation and only the rare occurrence of mutilating disease. This paper was followed by a description in 1958 of 118 patients with psoriasis and an erosive arthritis [3]. The majority of patients were found to have an arthritis indistinguishable from rheumatoid arthritis. Although no attempt had been made to exclude rheumatoid arthritis patients from this group, only 1 per cent of them were seropositive compared to 8 per cent of patients with definite rheumatoid arthritis. In this study, it was noted that deforming arthritis as well as arthritis mutilans was associated with an earlier age of onset of joint disease, and with sacroiliitis. In 196 a second study of this group of patients was reported [15]. Again, the majority of patients (9 per cent) belonged to the group that was indistinguishable from rheumatoid arthritis, while 16 per cent belonged to the distal group, and 5 per cent constituted the 'deforming' group with spinal abnormalities and severe deforming peripheral joint disease. They concluded that only a small proportion of patients with psoriatic arthritis developed severe arthropathy, in spite of the frequency of polyarthritis 'indistinguishable from rheumatoid arthritis'. In a review paper in 193 [5], Moll and Wright summarized their concept of psoriatic arthritis as an inflammatory arthritis associated with psoriasis, usually seronegative, and described the five clinical patterns. It is of note that while in previous studies by Wright, the group indistinguishable from rheumatoid arthritis was the most common, the 193 paper described the 'symmetric polyarthritis' in 15 per cent of the patients while an 'asymmetric' group emerged as the most common, occurring in per cent of their patients. Although initially noted by Wright, Little et al. [11] and Leonard et al. [12] also point out the association of arthritis with severe psoriasis. Both studies reported a much higher frequency of arthritis among patients with psoriasis than had been previously described. In his analysis of 3 patients, Leonard confirmed the distribution into five clinical patterns, while Little did not describe the clinical features in his patients.

13 Psoriatic Arthritis (PSA) -An Analysis of 22 Patients 139 In a large study of 1 patients by Kammer et al. [14], the clinical description unfortunately did not adhere to the patterns described by Moll and Wright. Rather they divided the patients into those with an asymmetric oligoarthritis, those with symmetric polyarthritis, and patients with back disease. The last group included patients with peripheral joint disease belonging to the other groups. Distal joint disease seemingly did not occur by itself. They commented that half of their patients had destructive forms of arthritis. More recently, Scarpa et al. [16], described the clinical features of arthritis in 62 patients with psoriasis, and confirmed the classes described by Moll and Wright, although in a slightly different frequency. These studies did not exclude patients with rheumatoid arthritis or any other known rheumatic disease. The aim of our study was to identify the clinical patterns of psoriatic arthritis among patients fulfilling the accepted definition of the disease, rather than merely having arthritis with psoriasis. We therefore excluded patients with other conditions from our clinic. We did not attempt to assess the frequency of psoriatic arthritis among patients with psoriasis. However, the Psoriasis Education Research Center, which serves as a referral center for patients with psoriasis, has 25 patients registered, whereas our series consists of 22 patients collected over the same period of time, thus giving a rough frequency of psoriatic arthritis of 1 per cent. Our patient population is similar to those previously reported. Table 6 compares the demographic data of our patients to the studies described above. The slight female preponderance was noted in previous studies [2,14]. However, comparing the subsets of patients with psoriatic arthritis shows a male predominance for those with the back disease and distal pattern (Table 5). Age of onset of both skin and joint disease are similar in all series. However, patients who have back disease tend to be older at onset of joint disease. Nail lesions occurred with a high frequency in all reported series. The onset of joint disease relative to skin disease is similar in all studies, with the majority of patients presenting with psoriasis either before the onset of arthritis or at the same time. There is, however a 1 to 3 per cent frequency of patients TABLE 6. Comparison of reported series M/F Age (years) Age onset (skin) (years) Age onset (joints) (years) Family history (%) Nail lesions (%) Skin<joints (%) Simultaneous (%) Joints<skin (%) Asymmetric oligoarthritis (%) Symmetric polyarthritis (%) Distal (%) Back (%) Mutilans (%) Sacro-iliitis (%) Rheumatoid factor (%) Gladman (1985) 14/ (16*) 19 (31*) 12 2 (33t) Wright (1956) ot Little (195) Leonard (198) 16/ (5S.14A.1D) Kammer (199) 45/ D54 ±D Scarpa (1984) 33/ If patients with oligoarthritis or polyarthritis have back disease as well, t If all patients with back disease are included. % Patients were rheumatoid factor negative by definition

14 14 D. D. Gladman and others presenting with joint disease before the diagnosis of psoriasis is made. In these patients nail lesions should be sought. It is of interest that in the previous series there appear to be no patients who have polyarthritis with an asymmetric distribution, nor patients with symmetric oligoarthritis. This may have resulted from different definitions of polyarthritis and symmetry used by the various investigators. Polyarthritis (>5 joints) was the most common clinical type of psoriatic arthritis in our series, and patients were equally divided between symmetric and asymmetric patterns. We have noted previously the high frequency of HLA DR4 in patients with psoriatic arthritis who have a symmetric polyarthritis similar to rheumatoid arthritis, although they are seronegative [26]. While the difference between symmetric and asymmetric polyarthritis may not be clinically important, it appears that polyarthritis in general denotes more severe disease. Deformity and damage, seen both clinically and radiologically, were observed in a significant number of patients. In fact, the frequency of severe disease is similar to that reported for rheumatoid arthritis [2]. Functional limitation to class III or IV was seen in 11 per cent of our group, again attesting to the fact that psoriatic arthritis may not be as benign as has been suggested. The patients described in this study were referred to a University-based clinic, and may not therefore be representative. However, as stressed, the majority of our patients were referred by dermatologists, a common pattern for referral in general. Also, the demographic data are similar to the other reported series. It would appear, therefore, that our patients are not a biased selection of unusually severe disease. If psoriatic arthritis is not as mild a disease as previously thought, more attention should perhaps be paid to earlier, more aggressive treatment. It is of interest in this regard that in our study patients treated with one disease-remittive agent (gold) had more damaged joints than those not treated, or treated wtih other disease-remittive agents. This may simply reflect the reluctance to use such an agent until definite evidence of damage appears. Although evidence of the efficacy of these drugs in treatment of psoriatic arthritis awaits confirmation, we should perhaps be considering their introduction more often and earlier, particularly in those with persistent polyarticular disease. ACKNOWLEDGEMENTS The authors wish to thank Mr John Hendrix for computer analysis, Mrs Betty Scheid for secretarial help, Drs Walter Silecky, Sherita Fox, Arthur Karasik, and Michael Sugai for their participation in the psoriatic arthritis clinic, and Dr M. B. Urowitz for confirming the radiological evaluation. REFERENCES 1. Wright V. Psoriasis and arthritis. Ann Rheum Dis 1956: 15: Wright V. Rheumatism and psoriasis. A Reevaluation. Am J Med 1959; 2: Wright V. Psoriatic arthritis: a comparative study of rheumatoid arthritis and arthritis associated with psoriasis. Ann Rheum Dis 1961; 2: Wright V, Moll JMH. Psoriatic arthritis. Bull Rheum Dis 191; 21: Moll JMH, Wright V. Psoriatic arthritis. Semin Arthritis Rheum 193; 3: Wright V, Moll JMH. Psoriatic arthritis in seronegative polyarthritis. Amsterdam: North Holland Publishing Co, 196: Avila R, Pugh DG, Slocumb CH, Winkelmann RK. Psoriatic arthritis: a roentgenographic study. Radiology 196; 5: Baker H. The relationship between psoriasis, psoriatic arthritis and rheumatoid arthritis. An epidemiological, clinical and serologica] study. MD thesis, University of Leeds, Moll JMH. Psoriatic arthritis (editorial). Br J Rheumatol 1984; 23:

15 Psoriatic Arthritis (PSA) - An Analysis of 22 Patients Wright, V. Psoriatic arthritis. In: Kelly EN, Harris ED, Ruddy S, Sledge CB, eds. Textbook of rheumatology. Philadelphia: W. B. Saunders Co, 1981: Little H, Harvie JN, Lester RS. Psoriatic arthritis in severe psoriasis. Can Med Assoc J 195; 112: Leonard DG, O'Duffy JD, Rogers RS. Prospective analysis of psoriatic arthritis in patients hospitalized for psoriasis. Mayo Clin Proc 198; 53: Molin J. Psoriatic arthritis. Ann Clin Res 198; 8: Kammer GM, Soter NA, Gibson DJ, Schur PH. Psoriatic arthritis: A clinical, immunologic and HLA study of 1 patients. Semin Arthritis Rheum 199; 9: Roberts MET, Wright V, Hill AGS, Mehra AC. Psoriatic arthritis, follow-up study. Ann Rheum Dis 196; 35: Scarpa R, Oriente P, Pulino A, et al. Psoriatic arthritis in psoriatic patients. Br J Rheumatol 1984; 23: Carson DA. Rheumatoid factor. In: Kelley WN, Harris ED, Ruddy S, Sledge CB, eds. Textbook of rheumatology. Philadelphia: W. B. Saunders Co, 1981: Steinbrocker O, Traeger CH, Batterman RC. Therapeutic criteria for rheumatoid arthritis. JAMA 1949; 14: Cooperating Clinics Committee of the American Rheumatism Association: A seven-day variability study of 499 patients with peripheral rheumatoid arthritis. Arthritis Rheum 1965; 8: Lansbury J. Report of a three-year study on the systemic and articular indexes in rheumatoid arthritis. Theoretic and clinical considerations. Arthritis Rheum 1958; 1: Hoppenfeld S. Physical examination of the spine and extremities. New York: Appleton- Century-Crofts, Miller MH, Lee P, Smythe HA, Goldsmith CH. Measurement of spinal mobility in the saggital plane: new skin contraction technique compared with established methods. J Rheumatol 1984; 11: Bennett PH, Burch TA. In: Bennett PH, Wood PHN, eds. The epidemiological diagnosis of ankylosing spondylitis. Proceedings of the 3rd international symposium of population studies of the rheumatic diseases, New York, New York: Excerpta Medica Foundation, 1968: Bywaters EG, Dixon AS: Paravertebral ossification in psoriatic arthritis. Ann Rheum Dis 1965; 24: Resnick D. Radiology of seronegative spondyloarthropathies. Clin Orthoped Rel Res 199; 143: Gladman DD, Anhorn KAB, Schachter RK, Mervart H. HLA antigens in psoriatic arthritis. J Rheumatol 1986; 13: Gordon DA, Stein JL, Broder I. The extra-articular features of rheumatoid arthritis. A systematic analysis of 12 cases. Am J Med 193; 55: