There are various extracutaneous manifestations of psoriasis. Of these, psoriatic arthritis (PsA), a seronegative spondyloarthropathy (SpA), is one. This entity was first recognized more than 100 years ago, but its clinical manifestations and pathogenesis are still being delineated to this date [2]. The prevalence of arthritis in patients with psoriasis varies. Studies have shown that PsA affects from 5 to 25 % of patients with psoriasis and can vary not just by degree of skin involvement but also by geographic area [1, 3, 4]. The clinical spectrum of the disease can be influenced by diet, climate, and microorganisms which differ by geographic locations [5].

PsA is defined as a SpA with characteristic skin and nail findings. There are a variety of articular features that can occur in patients with PsA. The most common is polyarthritis, a symmetric arthritis involving more than 5 joints. Other clinical subsets are spondylitis with or without peripheral arthritis, distal interphalangeal arthritis (see Fig. 32.2), asymmetric mono-oligoarthritis, and arthritis mutilans [2]. It may also be grouped into patients that show peripheral articular disease or axial disease with radiologic sacroiliitis. The peripheral pattern occurs more commonly than the axial pattern. Of patients with axial disease, nearly half of the patients are HLA-B27 positive [2]. Patients who are HLA-B27 positive have earlier disease and have been noted to have a shorter interval between onset of skin manifestations and joint disease [6, 7]. Given these distinct subsets, the clinical course of PsA may vary. Some studies, however, have shown that men show less disease progression than women [8]. In addition, the relationship between skin manifestations and severity of joint disease is still unclear. Most patients develop skin lesions prior to joint disease. Some studies have found that patients with active arthritis tend to have milder skin disease but others have found an inverse relationship [9, 10]. Other studies have found no relationship between skin disease and severity of joint disease [11].

The correlation between severity of extra-articular manifestations and joint inflammation has been evaluated. Nail involvement can be seen in all forms of psoriasis but is more common in patients with psoriatic arthritis occurring in 50–90 % of patients with the disease [10, 12, 13]. The nail findings most commonly consist of pitting and yellow discoloration of the fingernails. In more severe cases there may be onycholysis. As opposed to skin disease, it has been noted that the severity of a patients’ nail findings correlates with their joint disease [14].

Uveitis is reported to be the most common extra-articular manifestation of the SpAs [15]. The association between PsA and uveitis has been well documented. The likelihood of a patient with acute anterior uveitis to have PsA is reported to be less than 1 %, however the occurrence of uveitis is up to 25 % in patients with PsA (Table 32.1 and 32.2) [16, 17]. The prevalence of uveitis has been reported to be higher in women however this is variable [20–22]. Joint disease generally precedes eye manifestations but some reports have shown ocular inflammation as the initial presentation of PsA [18].

The first report of the association between eye manifestations and PsA was in the 1970s [19]. Lambert and Wright described the eye manifestations of 112 patients with PsA. The authors noted 31 % of patients had some form of ocular inflammation. Conjunctivitis was the most common followed by iritis, episcleritis, and keratoconjunctivitis sicca (Table 32.3). Of the patients found to have iritis, 43 % had sacroiliitis and 28.5 % had spondylitis. There was a higher prevalence of iritis in patients with axial disease when compared to other patients. The authors were the first to conclude that eye inflammation was a frequent complication of psoriatic arthritis, and this was the first study to address the concept of PsA as a seronegative SpA.

Most of the literature since has evaluated PsA associated uveitis in comparison to the uveitis found in other seronegative SpAs which includes ankylosing spondylitis (AS), reactive arthritis (formerly known as Reiters syndrome), arthritis associated with inflammatory bowel disease (IBD), PsA and undifferentiated SpA [17, 20]. These studies have shown that the prevalence and clinical characteristics of uveitis associated with each type of SpA can vary significantly (Table 32.2).

Patients with PsA predominantly have uveitis that is insidious in onset, continuous and bilateral with a high rate of recurrence (Table 32.2). [20, 21] In addition, this patient population is more likely to have posterior involvement than seen in other types of SpAs. Uveitis is equally represented among patients with axial and peripheral joint disease with half of patient cohorts having peripheral joint disease alone and the other half having a combination of axial disease alone or both [22]. However, other authors have found variable risk factors such as extensive axial involvement, specifically sacroiliitis, and dactylitis [21, 22]. It has been noted that patients with axial disease and uveitis tend to have a distinct clinical picture from the more common presentation and is clinically more similar to the uveitis seen in patients with AS. [21] This presentation is more often of acute onset with predominantly anterior chamber inflammation.

Given the unique features that are associated with pediatric uveitis, special attention should be given to PsA associated uveitis in children. Juvenile psoriatic arthritis (JPsA) is a distinct clinical entity, defined as a chronic inflammatory arthritis associated with psoriasis. It is considered a distinct subtype of juvenile idiopathic arthritis (JIA) based on observations that patients with JPsA have a form of juvenile idiopathic arthritis that differs both in its clinical manifestations and in its outcome than that noted in adults [23]. JPsA represents up to 10 % of all JIA subtypes and has a predilection for females. Anti-nuclear antibodies (ANAs) are positive in more than 50 % of affected patients [24]. Uveitis has been reported to occur in 10–15 % of JPsA patients. Other series have reported a much higher prevalence (Table 32.4). In addition, it has been reported that up to 13 % of children with chronic uveitis will have JPsA [28].

Heiligenhaus et al. [35] looked at the prevalence and complication rates of uveitis in the different subtypes of JIA. The authors noted 75 % of patients with early-onset JPsA had asymptomatic uveitis and inflammation present on routine screening. This was the same in both oligoarticular and polyarticular arthritis patients. This was in contrast to JIA patients with HLAB27 associated eye inflammation and late onset JPsA (>6 years) that was typically symptomatic. The authors also noted a low rate of complications compared to the other subtypes of JIA patients with only 25 % developing ocular complications [25].

Butbal et al. [26] compared the clinical features of patients with JPsA and JIA. The authors divided each group into patients with oligoarticular disease and polyarticular disease. They found that in patients with oligoarticular disease there was no difference in the rate of uveitis between the two groups, at 19 %. However in patients with polyarticular disease, the prevalence of uveitis in patients with JPsA was 23.8 % compared to 0 % of the JIA patients. However, the authors noted that this low prevalence of uveitis in their polyarticular JIA cohort had not been previously reported and was likely due to small sample size. Otherwise there was no statistical difference between ANA positivity, type of uveitis (acute versus chronic), or rates of complications between the two groups.

In summary, the uveitis in JPsA patients tends to be more similar to that seen in JIA patients and different than adult PsA associated uveitis. Additionally, pediatric patients should be monitored closely for asymptomatic ocular inflammation as they may have a worse visual prognosis.

The association between psoriasis without arthritis and uveitis is not as well established but will be briefly discussed. The first report that associated psoriasis with uveitis was in 1979. Knox reported 10 patients with uveitis diagnosed with psoriasis [27]. They concluded that there was a rare but important correlation between eye inflammation and skin disease. Following this, more comprehensive studies found that most patients with uveitis and psoriasis also have arthritis at presentation [28, 29]. Given this correlation, some feel the prevalence of uveitis in patients with psoriasis without arthritis is not significant. However, more recent studies have shown evidence that an entity of psoriatic uveitis without arthritis does exist.