Several aspects of psoriatic arthritis make it hard to answer questions about its treatment succinctly.
First, there are at least three forms of psoriatic arthritis: in some patients it looks very much like rheumatoid arthritis, in others like ankylosing spondylitis, and in still others only the end joints of the fingers (and, usually, the fingernails) are involved. What may work for one type of psoriatic arthritis may not for another.
Second, although most doctors think all inflammatory rheumatic diseases are autoimmune, it has been very hard to identify specific problems with the immune system in patients with psoriasis or psoriatic arthritis. Since most treatments for autoimmune disease change the function of specific parts of the immune system, it is hard to know which function to identify as a potential target when you are not even certain that the immune system has gone awry.
Third, compared to rheumatoid arthritis, psoriatic arthritis is fairly uncommon. It is an 'orphan' disease, and most treatments that are tried have been borrowed from another disease rather than specifically developed for psoriatic arthritis.
That said, much has happened in the last few years. For at least the past two decades, the standard treatment for psoriatic arthritis has included nonsteroidal anti-inflammatory drugs, sulfasalazine and, in more severe cases, methotrexate or cyclosporin. Corticosteroid drugs such as prednisone have not been very effective. Methotrexate, the most effective, has the added advantage that it treats the skin condition as well as the joints, but even with it many patients failed to respond well. Drugs useful in treating the skin disease, such as acitretin (Soriatane), sometimes work in refractory cases but are often toxic.
About 5 years ago the dramatic success in rheumatoid arthritis of the new class of drugs called biologics, specifically inhibitors of a small chemical called tumor necrosis factor alpha led to trials of these drugs in psoriatic arthritis. In brief, TNF alpha inhibitors -- etanercept (Enbrel) and infliximab (Remicade) - work extremely well in many patients with psoriatic arthritis of all three types,,. Adalimumab (Humira) is a very recently released similar drug that may be expected to work as well. These drugs may work by inhibiting TNF alpha or by breaking the inflammatory cycle in a different way. TNF alpha inhibitors also appear to protect bone from being eaten away. In clinical trials, these drugs reduce inflammation and prevent deterioration over several years, and they improve skin disease as well.
As a result of success with TNF alpha inhibitors, other biologics, which have different effects on the immune system, are now under trial,,. The down side is that all of these drugs are extremely expensive, that they are injectable rather than available in pill form, and that their major side effect is that they make recipients susceptible to certain kinds of infections. Otherwise they are not particularly difficult to take. Specific information about these drugs can be found elsewhere on this website.
The details of how these biologics affect the immune system is less important than the fact that they do work in psoriatic arthritis. In doing so, they teach us that the immune system is abnormal in psoriatic arthritis, that very specific abnormalities can be corrected, and that the development of treatments based on an immunological theory of this disease is valid. Thus, in the next several years, we can expect to see many more immunologically active drugs - largely biologics - developed for and tried in psoriatic arthritis. With luck, one or more of the new drugs will be inexpensive, orally administered, side-effect free, and possibly even curative.
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