Psoriatic arthritis (PsA) is often described as a chronic, inflammatory arthropathy affecting the distal interphalangeal joints (DIP) of the hands, metatarsophalangeal joints (MTP) of the feet, and spine in association with psoriasis. One to three percent of the world population has been diagnosed with psoriasis . with usually a negative serological test for rheumatoid factor and the absence of rheumatoid nodules .
However, more recent, large questionnaire-based studies have indicated that the real prevalence may be much higher. Thus, a Scandinavian study revealed arthritis in 30% of psoriatics and in the USA, 23% . In general, it appears that there is no direct relationship between the extent and severity of psoriasis and of psoriatic arthritis Further, nail disease is more frequent in cases with arthritis. A review of population-based studies estimated the population prevalence of psoriatic arthritis at 0.02–0.1% . There appears to be a stronger association with generalized pustular psoriasis or erythrodermic psoriasis and arthritis. Overall, men and women are affected equally by psoriatic arthritis. However, a male predominance occurs in the spondylitic form and a female predominance occurs in the rheumatoid form. Psoriatic arthritis usually develops in the fourth to sixth decades of life, but it can occur at almost any age.
Characteristic features of psoriatic arthritis include: swelling, erythema, warmth, and inflammation of the affected joint. PsA can present with asymmetrical joint distribution, involving more joints over time and progressing as an oligoarticular/polyarticular disease. Almost any joint can be involved including peripheral (e.g., the DIPs) and/or axial joints (e.g., spine and sacroiliac joints). PsA can also manifest with involvement of periarticular structures such as tenosynovitis (inflammation of the tendon sheath), dactylitis or "sausage digit" (inflammation of entire digit), and enthesitis (insertion of the tendon). These features/Extra-articular features may include inflammation of the eye (Systemic symptoms are usually limited to ocular involvement, which affects 30% of patients with psoriatic arthritis, mucousmembranes, urinary system, and cardiovascular system (i.e., iritis, conjunctivitis, aortic dilation, and urethritis) .
Scaly, erythematous plaques; guttate lesions; lakes of pus; and erythroderma are all types of psoriatic skin lesions that may be seen in the context of psoriatic arthritis. Nail pitting, Beau lines, leukonychia, onycholysis (the nail plate is becoming detached from the nail bed), oil spots, subungual hyperkeratosis, splinter hemorrhages, spotted lunulae, and cracking of the free edge of the nail all support the diagnosis of psoriatic arthritis, especially of the distal interphalangeal (DIP) joint type. In fact, psoriatic nail changes may be a solitary finding in patients with psoriatic arthritis.
Due to the broad spectrum of PsA there has been a need to create subgroups like
1- Pain in joints on both sides of your body Predominantly peripheral mono- or asymmetrical oligoarthritis is the most common form, and often overlooked. 4 large joints are affected, often with acute scattered involvement of the metatarsophalangeal, proximal interphalangeal, and DIP joints. Sausage digits due to inflammation of the flexor tendons and synovium and pitting edema of the distal extremities may be observed.
2- Pain in your finger joints Predominantly distal interphalangeal arthritis, the well recognized classical form, but less common than previously emphasized, occurs in approximately 5-10% of patients with psoriatic arthritis. One or several DIP joints may be involved. Periarticular swelling and acute inflammation with warmth and rubor may occur. DIP joint involvement and concomitant nail involvement with acute paronychia is a characteristic picture.
3- Predominantly symmetrical, rheumatoid-like, rheumatoid factor-negative polyarthritis, usually less severe than rheumatoid arthritis. Predominantly symmetrical, rheumatoid-like, rheumatoid factor-negative polyarthritis, usually less severe than rheumatoid arthritis, occur within the small joints of the hands and the feet, the knees, and the elbows and This form affects as many as 25% of patients .
4- Destructive arthritis ‘Arthritis mutilans’, a relatively uncommon, occurring in 5% of patients with psoriatic arthritis severely deforming arthritis involving fingers and toes predominantly. causes a telescoping motion of the digits, noted as opera-glass deformity or pencil-in-cup radiographic findings. Fever may accompany arthritis mutilans
5- Pain in your spine. Predominantly axial arthritis: psoriatic spondylitis and/or sacroiliitis, with or without variable peripheral arthropathy. Spinal involvement may be clinically silent, but radiological examination suggests that it may affect about one-third of all cases of psoriatic arthritis. Clinically, this form may involve: (i) both spine and sacroiliac joints, as in idiopathic ankylosing spondylitis; (ii) sacroiliac joints alone; and (iii) spine alone. It may be less disabling than the idiopathic form . Male patients are more frequently affected than female patients.
6- Psoriatic nail lesions, soft tissue thickening above the terminal phalanx, and radiologic involvement of the phalanx with periosteal reaction and bone have been described under the term psoriatic onychopachydermoperiostitis (POPP). POPP must be differentiated from other forms of psoriatic arthritis, especially the DIP joint type. A periosteal reaction of the terminal phalanx in the absence of DIP joint involvement is characteristic of POPP. In addition, pain and soft tissue thickening is more common in POPP. Nail disease is common to both POPP and DIP psoriatic arthritis. The nails of the great toes are involved in most reported cases of POPP .
7- Juvenile psoriatic arthritis is usually mild and often monoarticular. Tenosynovitis and nail involvement are common. Sacroiliitis is associated with HLA-B27 positivity. When unfused epiphyses are inflamed, disordered bone growth and foreshortening can result. Children have a higher frequency of simultaneous onset of psoriasis and psoriatic arthritis.
Temporomandibular joint involvement. This may manifest as local pain, often aggravated by eating and may progress to ankylosis requiring surgical managementOrthopan-tomographical examination showed that 31% of patients with psoriatic arthritis had radiographical changes in the condyle of the temporomandibular joint, as compared with 13% of controls . Computed tomography may reveal changes not visible on conventional radiography. Sternal joint involvement. This is becoming increasingly recognized but is unusual as an initial manifestation .
Causes/ etiology and pathogenesis :
Although the exact cause of psoriatic arthritis is unknown, genetic, environmental, immunologic, and vascular factors contribute to one's predisposition .
Genetic factors
Approximately 40% of patients with psoriasis or psoriatic arthritis have first-degree relatives who are affected. The sibling occurrence risk is approximately 8%. Although concordance rates of psoriatic arthritis in twins are not yet known, a 65-72% concordance rate of psoriasis exists between monozygotic twins, compared with a 15-30% concordance for dizygotic twins. A 65-72% concordance exists between monozygotic twins compared with a 15-30% concordance for dizygotic twins .In general, results concur with studies of cutaneous disease, with genetic susceptibility loci such as HLA Cw6, B13, B17,B7, B27, B57,B39,HLA-DR4, HLA-38, HLA-DR7 and DR3 occurring most frequently.
The following associated gene polymorphisms are also thought to be associated with psoriasis and psoriatic arthritis such as TNF-alpha promoter, MHC class I-chained related gene A (MICA), Caspase-activating recruitment domain (CARD) 15, Interleukin (IL)–12/IL-23p40 and IL-23 receptor .
Caspase-activating recruitment domain (CARD) 15, a molecule involved in macrophage–monocyte cell signalling, has been implicated as a candidate gene, at least in some patients . This molecule has also been implicated in Crohn’s disease but not in cutaneous psoriasis.
Environmental factors: Studies of families in which psoriatic arthritis aggregates suggest an important environmental component to disease pathogenesis. Increased immunoreactivity to streptococcal antigens has been reported in sera of patients, but establishing a pathogenic link has proved elusive and appears much more tenuous than for the skin disease. An increased prevalence of psoriatic arthritis has been reported in HIV and hepatitis C infection, and antibodies to enterobacterial antigens are also recorded .
Trauma as a precipitating event has also been noted. Interestingly, trauma appears to be more important in psoriatic compared to rheumatoid and other inflammatory forms of arthritis . Neuropeptides and the nervous system have been implicated in these events .
Immunologic factors: Much evidence suggests that a T-cell–mediated process drives the pathophysiology of psoriasis and psoriatic arthritis. Activated T cells may contribute to the enhanced production of cytokines found in synovial fluid. Th1 cytokines (eg, TNF-alpha, IL-1beta, IL-10) are more prevalent in psoriatic arthritis than in rheumatoid arthritis. Monocytes also play a role in psoriatic arthritis and are responsible for the production of matrix metalloproteinases, which may mediate the destructive changes in the joints of patients with psoriatic arthritis .
Vascular factors: Slight differences exist in the vascular patterns of joints in psoriatic arthritis compared with those of rheumatoid arthritis, suggesting possible different pathogenic mechanisms of these diseases.
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