Psoriatic Arthritis: A Look Back at Moll & Wright’s Landmark 1973 Paper

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Psoriatic arthritis came to be viewed as a distinct disease entity with specific clinical features, genetics and pathophysiology only gradually. One important historic development in this transition was a 1973 paper written by a pair of researchers out of Leeds, England: John M. Moll, BSc, DM, and Verna Wright, MD, FRCP.¹ Here we discuss the contributions of their paper and how it affected clinical judgments about the disease.

Early Studies in Psoriasis

In the 19th century, several French physicians wrote of the association of psoriasis with arthritis.² This included the first detailed description of psoriatic arthritis written by Charles Bourdillon in 1888.³ But interest in the disease lagged for several decades. Through case studies and small series, the first half of the 20th century saw a building pile of evidence concerning the association between psoriasis and arthritis.² The two were largely seen as separate diseases occurring coincidentally, although it was sometimes speculated that psoriasis might be one possible trigger of rheumatoid arthritis.^1,4

“There had been recognition that there was this association between psoriasis and arthritis back in the 19th century,” says Christopher Ritchlin, MD, MPH, a professor of medicine and chief of immunology and rheumatology at University of Rochester Medical Center, N.Y., “but this concept didn’t seem to be high in people’s minds after the initial descriptions. Basically, psoriatic arthritis was considered a form of rheumatoid arthritis.”

This view began to slowly change with the work of several titans of rheumatology. Dr. Wright, Harvey Baker, MB, Walter Bauer, MD, and others began writing of the relationship between psoriasis and arthritis in more detail, including its epidemiological, clinical, serological and histological characteristics.¹ Partly based on this work, the American Rheumatism Association (which later became the ACR) first included psoriatic arthritis in its classification of rheumatic diseases in 1964.⁵

Dr. Wright was a leader in the area, and he and his colleagues, working out of Leeds, performed much painstaking research on this topic. For several years, he worked closely with an associate, Dr. Moll. Together, the two published what came to be a critically influential paper, synthesizing and adding to our knowledge of the disease. Simply named “Psoriatic Arthritis,” the paper was published in Seminars in Arthritis & Rheumatism in 1973.¹ Since then, the 24-page paper has been cited almost 1,700 times.

The Paper

Dr. Ritchlin

“It was this manuscript from the Leeds group that really showed that psoriatic arthritis was a distinct form of arthropathy,” says Dr. Ritchlin. He notes that Dr. Wright was an astute clinical observer who kept copious notes on his patients. “He drew conclusions from what he saw in the clinic. He used these observations to test hypotheses and design studies to carry out the kind of work that led to the seminal findings in this manuscript.”

Luis Espinoza, MD, chief of rheumatology and a professor of medicine at the LSU School of Medicine, New Orleans, agrees the 1973 Moll and Wright manuscript marked an important milestone. “It defined the characteristics and distinctiveness of psoriatic arthritis and provided the basis for considering it distinct from rheumatoid arthritis,” he says.

Dr. Ritchlin adds, “This manuscript went into detail as to why that was the case—in really specific detail.”

In their paper, Moll and Wright provided historical background, discussed terminology and definitions, and reviewed in great detail the existing evidence surrounding psoriatic arthritis. They reviewed epidemiologic, clinical, radiological, laboratory and pathological evidence for psoriatic arthritis as a distinct disease entity. The team also discussed diagnostic problems, genetic and other possible etiological factors, as well as treatment and prognosis.¹

Notes Dr. Ritchlin, “There were people who were writing about this earlier, but no one had put everything together in the way this paper did.”

Definitions & Disease Subtypes
One of the paper’s most important and enduring contributions was the elucidation of disease definitions and detailed disease subtypes. In their paper, Moll and Wright pointed out there was no good existing definition of psoriatic arthritis in the medical literature. They discussed the wide spectrum of definitions being used, all of which they considered too specific. Instead, Moll and Wright adopted a broad definition of psoriatic arthritis: Psoriasis associated with inflammatory arthritis (peripheral and/or sacroiliitis or spondylitis), “usually with a negative serological test for rheumatoid factor.”¹

This was not just an academic exercise. “In order to define a disease, you really need a case definition,” says Dr. Ritchlin. “In this paper, they put together the case definition of what it is to have psoriatic arthritis.”

In addition to this, the team provided a detailed description of the various clinical presentations of the disease, which included some more specific features, such as dactylitis. They wrote, “The classical picture of psoriatic arthritis having a predilection for the [distal interphalangeal joints] should be revised. It is clear from more extensive clinical surveys that a variety of presentations ranging from single ‘sausage’ digits to arthritis mutilans may be observed.”¹

In 1959, in an earlier publication, Dr. Wright had proposed three subcategories: predominant distal interphalangeal disease, severely deforming arthritis (which included those with axial disease) and rheumatoid-like disease.⁶ In this paper, the team revised this earlier characterization to describe five broad clinical groups of psoriatic arthritis: predominant distal interphalangeal joint disease, asymmetrical oligoarthritis, symmetrical polyarthritis (which might resemble rheumatoid arthritis in appearance), spondylitis and arthritis mutilans.¹

In so doing, the team acknowledged that “There is often no clear division between one type of presentation and another.” They also noted that peripheral joints may also be involved in a case of predominant spondylitis and that patients with arthritis mutilans also often had sacroiliitis. In other words, a degree of fluidity between these presentations often existed.¹

“They really took all of these earlier reports and distilled them into these subgroups. Those were really helpful for clinicians in thinking about diagnosis, and in some cases really helping [us] understand clear differences between other forms of arthritis—[such as] rheumatoid arthritis,” says Dr. Ritchlin. “They were able to [give] a case definition and go into great detail on the heterogeneity and the characteristics of those subsets.”

Some later researchers have proposed modifications to these subtypes in terms of disease classification, although Dr. Ritchlin believes these subtype descriptions have held up fairly well over time.⁷ “What we do see is a lot less arthritis mutilans than we did, and we don’t know why,” he adds.

Whether these subcategories represent distinct, but overlapping, pathophysiologies is unknown. It does appear the association of the B27 human leukocyte antigen (HLA) haplotype may be stronger for the predominantly spondylitis form than for other subtypes.⁸ But in terms of current treatment guidelines, distinctions between severe and/or treatment-resistant disease compared with less severe disease are much more important than the particular subtype presentation.⁹