ORIGINAL ARTICLE Pyoderma gangrenosum and underlying diseases in Japanese patients: A regional long-term study Sae INOUE, 1 Jun-ichi FURUTA, 1 Yasuhiro FUJISAWA, 1 Saori ONIZAWA, 1 Shusaku ITO, 2 Masayuki SAKIYAMA, 3 Keiko KOBAYASHI, 4 Toshiyuki KANOU, 5 Shigeruko IIJIMA, 6 Tsunao OHI, 7 Chimaki OKUBO, 8 Yoshihiro MORIYAMA, 9 Naoko OKIYAMA, 1 Manabu FUJIMOTO 1 1 Department of Dermatology, Faculty of Medicine, University of Tsukuba, 2 Hitachi General Hospital, Ibaraki, 3 National Defense Medical College Hospital, Saitama, 4 Mito Red Cross Hospital, 5 Ibaraki Prefectural Central Hospital, 6 Mito Saiseikai General Hospital, 7 Tokyo Medical University Ibaraki Medical Center, 8 Mito Medical Center, 9 Tsuchiura Kyodo General Hospital, Ibaraki, Japan ABSTRACT Pyoderma gangrenosum (PG) is a chronic inflammatory disease of unknown cause that presents as an inflamma- tory and ulcerative disorder of the skin. PG is often associated with an underlying systemic disease. However, the frequencies of the underlying diseases are unclear in Japanese patients. In this retrospective, observational study, all patients diagnosed with PG who visited dermatology departments of nine regional hospitals in and around Ibaraki Prefecture were collected from 1982 to 2011 or 2014. The diagnoses of PG were based on the characteris- tic clinical and histological appearances and ruling out of infection. Sixty-two PG patients, including 29 males and 33 females, were identified. The ages of onset were 16–89 years, and the mean age was 50.2 years. Fifty (80%) of the 62 patients presented with an ulcerative PG, and the lower leg was the most common site (74%). Forty-six (74%) PG patients had underlying diseases. The most frequent was ulcerative colitis (32%), followed by myelodys- plastic syndrome (11%), rheumatoid arthritis (6%) and aortitis syndrome (5%). For treatment, 54 cases (87%) received systemic corticosteroids and 10 received additional treatment with cyclosporin. There was no significant correlation between underlying diseases and response to the initial treatment. Multivariate analysis revealed that the number of affected sites negatively correlated with successful initial treatment. Fifteen (24%) of the 62 cases relapsed. In conclusion, ulcerative colitis and hematological disorders were frequently associated with PG while approximately a quarter of the cases were idiopathic. Key words: epidemiology, hematological disease, pyoderma gangrenosum, treatment, ulcerative colitis. INTRODUCTION Pyoderma gangrenosum (PG), first described by Brunsting et al. in 1930, 1 is a chronic inflammatory disease of unknown cause that presents as an inflammation and ulceration of the skin. PG is characterized histopathologically by the accumula- tion of neutrophils in the skin, most commonly presenting as a rapid development of one or more painful, purulent ulcers with undefined borders on sites of normal or traumatized skin. PG is often associated with an underlying systemic disease. Among the strongest associations with PG are inflammatory bowel disease, hematological disorders and arthritis. 2–5 How- ever, the frequencies of the underlying diseases have not yet been documented in Japanese patients. The purpose of this study was to investigate the characteristics of the underlying diseases in Japanese PG patients and their corresponding treatments. METHODS In this retrospective, observational study, the medical records of all patients diagnosed with PG who visited the dermatology departments of nine regional hospitals mainly in Ibaraki Prefec- ture, Japan, were reviewed. The diagnosis of PG was based on characteristic clinical and histological appearances and the confirmed absence of infection. The reviewed periods were between 1982 and 2014 in two hospitals (The University of Tsukuba Hospital and Hitachi General Hospital) and between 1982 and 2011 in seven hospitals (National Defense Medical College Hospital, Mito Red Cross Hospital, Ibaraki Prefectural Correspondence: Yasuhiro Fujisawa, M.D., Ph.D., Department of Dermatology, Faculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan. Email: fujisan@md.tsukuba.ac.jp Received 26 March 2017; accepted 10 May 2017. 1 © 2017 Japanese Dermatological Association doi: 10.1111/1346-8138.13937 Journal of Dermatology 2017; : 1–4