It is recognized that patients with JPsA may be a heterogeneous group of patients who may present with features of similar to the other JIA subtypes. Two different classification systems of JPsA have been proposed, with the ILAR classification gaining increasing usage [1, 2]. Our findings are consistent with previous studies that suggested patients with JPsA comprise distinct populations that can be differentiated by the age of onset and clinical features [6, 11, 17, 18]. These results are similar to studies of adult patients with PsA that demonstrated subsets based on number of and/or location of joint involvement, symmetry and features of spondylitis [19–23].
The diagnosis of JPsA frequently occurs in patients who had been previously diagnosed with other forms of JIA with development of the diagnostic rash month to years later. We found that 1/3 of patients were diagnosed with another JIA sub-type prior to the diagnosis of JPsA after a mean of 4.2 years. In most of these patients a diagnosis of JPsA was not suspected based on clinic findings although some had a family history of psoriasis. In addition 3 patients with systemic JIA and psoriasis (data not shown), and 4 with RF+ polyarticular JIA and psoriasis could not be clinically differentiated from others with systemic or RF+ polyarticular JIA.
The most common course of arthritis found in the cohort was polyarticular course, present in 52% of patients which is similar to our incidence of polyarticular-course JIA in patients without psoriatic arthritis  but slightly lower than previous studies of JPsA [5, 6, 10]. Patients with polyarticular course could be distinguished from the other subtypes as they had a worse outcome, more severe clinical course, had more contractures, and longest mean time to first inactive disease. The pattern of arthritis differed as they were most likely to have involvement of the small joints of the hands and feet, to have symmetric disease, to require methotrexate and least likely to have hip and SI joint involvement. These findings would suggest that patients with polyarticular course JPsA form a distinct subset of JPsA patients that closely resemble patients with polyarticular course JIA without psoriasis.
The most common onset type was oligoarticular arthritis, present in 55% of cases with extension in approximately 1/3 of cases; an extension rate that is similar to that seen non-psoriatic oligoarticular onset patients [24–27]. Similarly, the clinical course of patients with both persistent oligoarthritis and extended oligoarthritis more closely resembled JIA clinical sub-types without psoriasis rather than other JPsA as a whole. At presentation found the frequency of wrist involvement of olgioarticular patients was closer to the frequency reported in oligoarticular JIA patients than the reported frequency of JPsA patients not subdivided [16, 28, 29]. These findings suggest that the clinical course of patients with oligoarticular onset JPsA more closely resembles that of oligoarticular JIA rather than an unsubseted JPsA cohort.
A previous study had suggested that there were 2 distinct groups of patients with JPsA based on age of onset of disease with the older patients resembling ERA patients without psoriasis . These older patients generally resembled the patients in our study with ERA and psoriasis in the pattern of joint involvement. Acute uveitis was only found in this group. Taken together these findings suggest that these patients older onset male patients more resemble patients with ERA without psoriasis than patients with other courses of JPsA. The prevalence of HLA-B27 was similar to previous reports in both ERA and JPsA with ERA features [5, 27, 30]. We suggest that this subgroup of patients should be classified and treated in the same manner as patients with ERA without psoriasis rather the ILAR current classification of undifferentiated. However, long-term studies are required to confirm this.
The overall outcome of patients in our study was excellent as during the course of disease 88% achieved inactive disease on therapy and 50% inactive disease off therapy. These rates are similar to previously reported remission rates depending on the definition of remission and the duration of the follow-up period . The majority of our patients did not have arthritis at last follow-up, 30% of patients were without active arthritis off all medication and only 10% had a contracture. We found that our patients tended to have linear growth along the predicted percentiles but that weight percentiles significantly increased. The significance of this finding is unknown but there have been reports that adults with psoriasis tend to be obese .