although psa was once described as a variant of rheumatoid arthritis ( ra ) , it has been included in the group of spondyloarthropathies .
psa was first defined by moll and wright in 1973 in patients who were seronegative for rheumatoid factor ( rf ) with positive history of psoriasis , current skin or nail psoriasis , and inflammatory joints of axial disease .
the exact estimation of psa prevalence among psoriasis patients is difficult because several epidemiologic studies on psa have not used validated criteria .
psa incidence has increased from 5% to 40% among patients with psoriasis [ 25 ] . because psa might be as common as psoriasis
approximately 40% to 60% of psa patients develop erosive arthropathy , and 17% have five or more deformed joints . a delay in diagnosis and treatment
dermatologists who lack expertise in psa might miss an opportunity for early treatment that could prevent functional joint disability .
unfortunately , many dermatologists are indifferent to psoriatic arthritis with any degree of severity and instead search for signs of hidden arthritis or skin disorders .
the association between arthritis and psoriasis was first described by alibert in 1818 and was designated psoriasis arthritique by bazin in 1860 . at that point , distinctive arthritis associated with psoriasis became widely accepted . however , in the 1950s , psa was grouped with ra as a  rheumatoid variant  or  rheumatoid spondylitis  .
subsequently , the distinct nature of psa was emphasized using clinical criteria . in 1973 ,
moll and wright defined psa and classified it into five subsets of distal interphalangeal arthritis , asymmetrical oligoarthritis , symmetrical polyarthritis , spondylitis , and arthritis mutilans .
although several diagnostic and classification criteria have been developed , they have not been commonly accepted .
physicians usually make a diagnosis of psa based on characteristic arthritis patterns together with the absence of rheumatoid factor and the presence of psoriasis skin and nail lesions
. since there are no specific serologic tests to confirm psa diagnosis , radiographs can be helpful . in 2006 ,
these criteria , called the classification criteria for psoriatic arthritis ( caspar ) , provide better sensitivity ( 91.4% ) than all previous criteria while maintaining high specificity ( 98.7% ) . to diagnose psa according to caspar , patients should have inflammatory joint disease ( peripheral , axial , or enthesitis ) with at least three points from the five categories .
caspar criteria can be modified for dermatologists who screen for psa among patients with skin psoriasis , as shown in table 1 .
the detection of psa requires detailed joint examination , which in not usually performed in a routine dermatologic clinic .
every psoriasis patient with musculoskeletal symptoms should ideally be referred to a rheumatologist , but this is impractical . a simple screening tool that identifies psoriasis patients who are more likely to have psa would be tremendously valuable to dermatologists and other healthcare providers
. a screening tool would also raise awareness in patients with psoriasis who are unaware of the relationship between psoriasis and musculoskeletal symptoms .
several appropriate psa screening tools have been developed and are used worldwide , including pest ( psoriasis epidemiology project ) , topas ( toronto psoriatic arthritis screening tool ) , and pase ( psoriatic arthritis screening and evaluation tool ) [ 1012 ] .
psa is a polygenic autoimmune disorder of unknown etiology in which genetic susceptibility , environmental factors , and immune mechanisms play crucial roles .
human leukocyte antigen ( hla)-c within the major histocompatibility complex ( mhc ) region is the strongest genetic association for psa .
other class i hla antigens associated with psa include hla - b13 , b27 , b38 , b39 , and b57 .
hla - b27 is present in 20% to 60% of psa patients , with increased incidence in the axial or spondylitic forms .
regarding hla class ii molecules , dr4 is more commonly found in the erosive form , while dr7 is more commonly found in peripheral involvement .
hla - b27 prevalence is much lower in axial psa than in ankylosing spondylitis ( as ) , and it is strongly influenced by ethnicity .
regarding immunopathogenesis , there is prominent lymphocytic infiltrate in both the skin and joints that is localized to dermal papillae in the skin and the sublining layer stroma in joint and inflammatory entheses .
t lymphocytes , particularly cd4 + cells , are the most common inflammatory cells , with a cd4+/cd8 + ratio of 2:1 in the synovial fluid and peripheral blood .
the inflammatory mechanism of psa involves autoproliferation of t cells as well as production of cytokines from type 1 helper t cells ( th1 ) and type 17 helper t cells ( th17 ) .
these include tumor necrosis factor ( tnf)- , interferon ( ifn)- , interleukin ( il)-1 , il-6 , il-8 , il-17 , il-22 , il-23 , and intercellular adhesion molecule ( icam)-1 .
high levels of tnf- , il-6 , il-8 , il-10 , and matrix metalloproteinases ( mmp ) are present in the joint fluid , psoriatic plaque , and serum of patients with early psa .
psa onset age is in the range of 30 to 50 years , and the condition affects men and women almost equally . in approximately 70% of cases , psoriasis precedes the development of psa by an average of 10 years . in approximately 15% of cases
, psa precedes the onset of psoriasis by more than 1 year , and in approximately 15% of cases the two conditions occur within 12 months of each other .
there are two major patterns of arthritis with psa : peripheral joint disease , which can be oligoarticular ( 4 involved joints ) or polyarticular ( 5 involved joint ) , and skeletal or axial disease with or without peripheral arthritis .
approximately 95% of patients with psa have involvement of the peripheral joints , predominantly the polyarticular form , while a minority has the oligoarticular form .
about 5% of patients have exclusively axial involvement , whereas 20% to 50% of patients have involvement of both the spine and peripheral joints , with peripheral joint involvement having predominance .
several other recent studies confirm that asymmetric oligoarthritis is the most common pattern in early phase psa .
involved joints in psa are usually less tender , less swollen , and less symmetric than in ra . as mentioned above , there might be ethnic differences in the pattern of joint involvement . in a korean study ,
patients with oligoarticular peripheral psa seem to have a shorter disease duration than patients with polyarthritis . dip arthritis and arthritis mutilans represent distinctive features of psa . in the largest clinical series , dip arthritis was reported in 1% to 59% of patients with psa . in this series ,
dystrophic nail changes , including pitting , subungal hyperkeratosis , and transverse grooves , are more frequent in psa than psoriasis . in roughly 5% of patients with longstanding disease ,
this leads to characteristic clinical features of  falling joints or  opera glass fingers , which is termed arthritis mutilans .
classical psa affects the distal interphalangeal ( dip ) joints , whereas ra affects the proximal interphalangeal ( pip ) joint more frequently .
another important differential diagnosis to consider in patients with psa is osteoarthritis ( oa ) .
however , the classic heberden s nodules in oa are bony spurs whereas the dip involvement in psa is merely joint inflammation .
morning stiffness and stiffness after prolonged inactivity are common in psa whereas stiffness tends to occur with joint activity in oa .
although psa occurs equally in males and females , oa of the hands and feet is more frequent in females .
dactylitis , enthesitis , and sacroiliitis are common in psa but are generally not present in ra and oa .
there are a wide variety of clinical manifestations and peripheral arthritic symptoms in axial psa that may overshadow those related to spinal inflammatory involvement .
however , asymptomatic involvement of the spine and sacroiliac joints may occur more often in psa than as .
furthermore , patients with axial psa have asymmetric disease that tends to be less severe . while the radiologic features vary , they can be helpful in detecting asymptomatic disease and differentiating axial psa from as .
however , bilateral fusion of the sacroiliac joint may occur with disease progression . in axial psa
, spondylitis may affect any spinal level in a skip fashion or it may affect only the cervical spine while sparing other tracts of the axial skeleton .
axial psa is characterized by a better prognosis than as , and patients with psa seldom progress to ankylosis .
enthesitis is usually defined by the presence of tenderness and swelling on palpation or pressure in the insertion sites of tendons , ligaments , or capsules .
enthesitis represents a hallmark of the clinical features of psa and is now regarded as the primary lesion .
achilles tendon enthesitis usually coexists with tenosynovitis and contributes to the  bomb - shaped tendon .
1 ) . it may occur in one or more digits concomitantly with the typical signs of inflammation , such as swelling , redness , pain , warmth , and limited range of motion .
it is an expression of active psa and will respond well to anti - tnf- therapy .
skin lesions such as psoriasis can be localized , diffuse , guttate , or pustular ( fig 2 ) .
thus , patients with any pattern and degree of arthritis can develop psoriasis vulgaris , severe generalized pustular psoriasis , or erythrodermic psoriasis .
iridocyclitis represents the most frequent extra - articular feature , with an estimated prevalence of 2% to 25% of cases .
iridocyclitis is characterized by an acute onset over 12 days , eye pain , redness , miosis , photophobia , and vision blurring .
what is the role of dermatologists in the field of psa  screening , diagnosis , or management ? some assert that if the primary problem is skin psoriasis , psa can be managed by a dermatologist .
if the chief complaint is a joint symptom , rheumatologists should primarily manage the patient with dermatologists assisting in the diagnosis of skin psoriasis .
dermatologists can conduct a full screening and confirm psa in psoriasis patients who are visiting a dermatologic department .
when managing psa , oligo- and dip arthritis can be managed by dermatologists , whereas polyarthritis , spondylitis , and arthritis multilans should be referred to rheumatologists ( fig .
more physicians have become aware of the relationship between psa , artherosclerosis , and increased cardiovascular risk in patients with psa .
psoriasis and psa should no longer be regarded as diseases limited to joint or skin .
clinical dermatologists should be thoroughly aware of the nature of psa , and an interdisciplinary approach is needed .
 psoriatic arthritis is a chronic inflammatory arthropathy associated with skin psoriasis . 
 it is considered a unique arthropathy with distinct clinical and radiologic features . up to 40% of patients with psoriasis 
 may develop psoriatic arthritis . 
 psoriasis usually precedes psoriatic arthritis , so dermatologists are in a critical position for screening patients of psoriatic arthritis early in the disease course . 
 psoriatic arthritis may be challenging to diagnose , especially for dermatologists , because it has an insidious disease course , non - specific symptoms , and no specific biomarkers . 
 psoriatic arthritis is a polygenic autoimmune disorder of unknown etiology , but immunologic roles have recently been validated . in recent years , treatment modalities have rapidly advanced in the fields of psoriasis and psoriatic arthritis . 
 biologic agents , including tnf- inhibitors and anti - il12/23 agents , have shown dramatic improvement . 
INTRODUCTION
CLASSIFICATION AND DIAGNOSIS
PATHOGENESIS
CLINICAL ASPECTS AND DIFFERENTIATION OF PSORIATIC ARTHRITIS
CONCLUSION