Spondyloarthritis in Japanese Patients

One of my favorite Japanese authors is Junichirô Tanizaki (1886 – 1985). He is one of the major writers of modern Japanese literature. Many parts of his stories are exploring the cultural identity of Japan, especially in the 20th century during which rapid changes occurred within the Japanese society, mainly because of an aggressive Westernization.

Japan is an island country and such geographic isolation (shortly) explains many of the differences observed in patients’ characteristics including genetics and co-morbidities whatever is the type of disease.

Spondyloarthritis (SPA) is a generic name regrouping several disorders as psoriatic arthritis, ankylosing spondylitis, reactive arthritis and enteropathic arthritis notably. It is to note that while gathered they are phenotypically distinct and categorized into axial or peripheral SPA, on the basis of primary symptom location.

It is usually considered as relatively rare in Japan. The estimated incidence rate is about 0.48/100,000 and the estimated prevalence 9.5 / 100,000 person-year in Japan. Which is less than 1/10 to 1/200, compared to Caucasians, respectively. (1-3)

Recent data extracted from the International ASAS COMOSPA database (Africa, America, Asia and Europe) and presented at the most recent EULAR congress in London are indeed showing by how much the clinical characteristics of spondyloarthritis in Japanese patients are looking different compared to the non-Asian patients and even to the other Asian patients.(4)

No surprise at all. In this database, most of the patients are presenting axial involvement but there is a great intercountry variability in various characteristics and co-morbidities.

Suspected reasons for such differences and low epidemiological numbers in Japan are environmental, late diagnosis or misdiagnosis, and genetics.

For example, HLA B27 is believed to be the strongest genetic factor associated with SPA but the incidence of HLA B27 is reportedly low as 0.4% in Japan. The frequency and the distribution of HLA B27 differ on ethnicity. HLA B27 as a diagnostic criterion may therefore not have much importance for Japanese patients. Instead, HLA B typing should be considered.(3)

That said the recent Westernization of the Japanese life style may increase such numbers and mitigate the differences with non-Asian. Indeed and interestingly, in the ASAS COMOSPA database, while globally different from others, Japan is likely never mentioned as extremes.(5)

The Westernization of the Japanese lifestyle has been shown to be associated with the increased prevalence of several risk factors for psoriasis, notably obesity and hyperlipidemia that are also risk factors for Psoriatic Arthritis. Hyperlipidemia is present in about 9.8% of men and 14.7% of women; both figures have been rising annually. In a recent study, the prevalence rate of Psoriatic Arthritis in patients with Psoriasis is very similar to rates reported in Western countries.(6)

I should confess that it would be unfair to only consider Westernization as the solo factor of increasing. Diagnostic methods improvement and increased awareness of PSA are surely contributing as well. No political matters here.

Additionally, and meanwhile different characteristics, innovative treatments have shown a similar favorable efficacy / safety balance in Japanese patients with SPA or Psoriasis patients with Psoriatic Arthritis and more results are expected soon. (7-11)

1. Ohara Y et al. Prevalence and clinical characteristics of psoriatic arthritis in Japan. J Rheumatol 2015; 42: 1439 – 42.
2. Kawada A. A survey of psoriasis in Japan from 1982 to 2001. J Dermatol Sci 2003; 31: 59 – 64.
3. Tam LA et al. Psoriatic Arthritis in Asia. Rheumatology 2009; 48: 1473 – 7.
4. Min C et al. Clinical characteristics of spondyloarthritis in Japanese Patients - EULAR 2016 - London - Abstract 1906.
5. Molto A et al. Prevalence and comorbidities and evaluation of their screening in spondyloarthritis: results of the international cross-sectional ASAS COMOSPA study. Ann Rheum Dis 2016; 75: 1016 – 23.
6. 2012 National Health and Nutrition Survey, Japan. Tokyo: Ministry of Health, Labor and Welfare; 2012.
7. Otsuka A et al. Clinical characteristics of Japanese patients with axial spondyloarthritis and short-term efficacy of adalimumab. J Orthop Sci 2015; 20: 1070 – 7.
8. Ohtsuki M et al. Secukinumab efficacy and safety in Japanese patients with moderate to severe plaque psoriasis: subanalysis from ERASURE, a randomized placebo-controlled phase 3 study. J Dermatol 2014; 41: 1039 – 46.
9. NCT01988103: Efficacy and Safety Study of Two Doses of Apremilast (CC-10004) In Japanese Subjects With Moderate-To-Severe Plaque-Type Psoriasis.
10. NCT02414633: Special Investigation in Patients With Psoriatic Arthritis (PsA) (Working Productivity and Activity Impairment (WPAI)).
11. NCT02750592: Study of Efficacy and Safety of Secukinumab in Japanese Patients With Active Ankylosing Spondylitis.