Aiming for Remission in Psoriatic Arthritis

Anna R Moverley, Laura C Coates, Philip S Helliwell

Disclosures

Int J Clin Rheumatol. 2014;9(2):147-153. 

In This Article

Natural History of PsA

PsA is a heterogeneous disease. Clinical manifestations vary from a mild, slightly troublesome oligoarthritis to a severe, mutilating polyarticular form. At any one time, the severity of skin and joint manifestations may be quite different. Generally, when and whether the skin clears, long-term skin sequelae (scarring) does not occur. The same cannot be said about the joints as it is likely that repeated episodes of inflammation will cause damage that cannot be repaired. Ideally, in that case, treating early and aggressively to achieve early remission should prevent this long-term damage. It is also pertinent to note that there is evidence of increased cardiovascular morbidity and mortality in both psoriasis and PsA – and in the case of psoriasis, this risk increases with increasing severity of skin disease.[9] It is not yet clear that achieving disease remission in PsA will reduce this risk.

Most early work in PsA suggested that, on the whole, this was a less severe form of arthritis when compared with rheumatoid arthritis.[10,11] It was acknowledged, however, that in some people the disease followed a particularly aggressive and deforming course. The initial cohort of patients collected by Wright in Leeds[4] was later reviewed by Roberts and the largely benign nature of the condition restated: 78% of a group of 178 patients were classified as 'mild' with only 11% of this group deteriorating over a follow-up period of more than 10 years.[12]

Further clinical studies have challenged the notion that PsA is a benign disease compared with rheumatoid arthritis.[13] Methodological differences may have accounted for some of these inconsistencies. For example, in comparative studies, cases should be appropriately matched with comparator conditions, something that was not always apparent in earlier studies. Another example, in longitudinal studies, would be the importance of maximizing follow-up – milder cases may be more likely to default, thus skewing the results towards a more severe outcome.

One explanation for these discrepancies may be that PsA is a heterogeneous disease both clinically and prognostically. Clinical experience would suggest, and some publications would support, the contention that up to a third of patients with PsA either have a mild, minimally progressive disease that requires only symptomatic treatment, or an oligoarticular disease limited to a few affected joints. The former group include those with arthralgia and low-grade inflammation – sometimes only a 'cold' swollen knee is observed over many years with little progression to joint damage. Later studies, particularly those from Toronto, have also hinted at a milder nonprogressive, oligoarticular group. For example, the first complete series published by Gladman included a large nonerosive group.[14] Subsequent series have looked at progression of damage and identified a group of 33–36% of patients who had no evidence of damaged joints at either presentation or follow-up.[15,16] A similar proportion of patients – 28% – remained without disability over a 10-year period.[17] An earlier study, looking at remission in PsA, using rather exacting criteria of no inflamed joints over three consecutive visits, found 18% of 391 patients fulfilled these criteria in an 18-year period. It is important to note, however, just over half of these subsequently relapsed.[18]

Wright reported a group of patients who developed a severely deforming arthritis, termed arthritis mutilans, with osteolysis of the digits, polyarticular involvement and frequent spinal involvement.[19] Subsequent reports have also described this most severe form of PsA, which results in marked disability.[20,21] Affected individuals often have flail digits in both hands and feet resulting in the 'main en lorgnette' deformity described by Wright. Fortunately, this distinctive subgroup only represents a small proportion of affected people, rarely more than 5% of the total. Between the mild, nonprogressive forms, and the severe arthritis mutilans, there is a predominantly polyarticular group in which progressive deformity and damage is slow but persistent. These people slowly accrue damage to joints and become progressively more disabled, as demonstrated by several cross-sectional and longitudinal surveys, particularly from the Toronto group.[13,22] In Dublin, follow-up of a cohort of patients presenting to the early arthritis clinic with recent-onset disease showed that 40% developed erosions by the 2-year assessment, a figure often used to emphasize the progressive nature of the disease.[23] In addition, a cohort from Bath demonstrated progression from oligoarthritis to polyarthritis and increasing disability during follow-up.[24]

Given the disease is often less benign than first thought, a treatment approach to quell any signs of inflammation should now be recommended, as in rheumatoid arthritis, although things may not be as straightforward in PsA. A study from the Toronto group demonstrated radiological progression of spinal disease in the absence of clinical progression (as indicated by symptoms and spinal movements) over a mean follow-up period of 57 months. Therefore, in this cohort, symptomatic and disease-modifying treatment did not prevent progression of the disease.[25] We can conclude that spinal 'damage' can progress in the absence of symptoms and it has also been shown recently that peripheral bone anabolic changes can progress despite abrogation of peripheral inflammation with a TNF inhibitor.[26]

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