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Yusho is recognized as a poisoning by a mixture of polychlorinated biphenyls (PCBs), dioxins and related compounds. We have continued a follow-up of skin symptoms in patients not only for supporting patients' health but also for understanding the possible prolonged effects of exposure to PCBs and dioxins in humans. We evaluated the severity grades and the skin severity scores of the symptoms who visited the annual examinations of Fukuoka prefecture from 2005 to 2007. Forty years have passed since the Yusho incident, and about 70% of the patients currently present no skin symptoms. In contrast, in about 30% of the patients, characteristic skin symptoms of Yusho, such as pigmentation of skin, black comedones and acneform eruptions, could still be observed. We analyzed statistical correlations between blood levels of PCBs or dioxin and skin severity grades.

We evaluated the severity grades and the skin severity scores of the skin symptoms who visited the annual examinations of Fukuoka prefecture in 2003 and 2004. The severity of skin symptoms improved significantly in the first 20 years; nowadays, however, further improvement can hardly be observed. More than 36 years have passed since the Yusho incident, and about 60% of the patients currently present no skin symptoms. In contrast, in about 40% of the patients, characteristic skin symptoms of Yusho, such as pigmentation of skin, black comedones and acneform eruptions, could still be observed. Using Peason's correlation coefficient test and Spearman's correlation coefficient test, we analyzed correlation between "PCB pattern" and the blood PCB concentration, the skin severity grade and the skin severity scores. However, we could not find out any obvious correlation.

We evaluated the severity grades and the skin severity scores of the skin symptoms of Yusho patients who visited the annual examinations in 2001 and 2002. The patients who participated in the examinations had been decreased gradually. However, because of enhancement of social interest, the number of the patients who visited the examination increased. The pattern of the severity grades and the severity scores was different from that of the past. A careful follow-up and analysis is required.

We analyzed the severity grades of the skin symptoms of Yusho patients who visited the annual examinations in 1999 and 2000. The severity grades of the skin symptoms clearly improved. The patients graded as 0 increased and those graded as II.III-III or III.IV-IV decreased as compared to the data in 1993. The pattern of the skin severity scores did not change much, although the patients who showed 0.1 reached 68% in 2000. The blood PCB concentration of Yusho patients also clearly decreased, especially in the patients who showed "A" pattern. Furthermore, the skin changes of the aged patients should be analyzed in detail in the future.

We analyzed the severity grades of the skin symptoms of Yusho patients who visited the annual examinations in 1997 and 1998. The severity grades of the skin symptoms clearly improved. The patients graded as 0 I-II increased and those graded as II III-III decreased as compared to the data in 1993 and 1994. The skin severity scores did not change much, although the patients who showed 0 or 1 reached more than 60% in both 1997 and 1998. The blood PCB concentration of Yusho patients also clearly decreased, especially in the patients who showed "A" pattern.

We reported the grades of severity of skin symptoms and the blood PCB patterns and concentrations in Yusho patients who had the annual examinations in 1995 and 1996. The skin severity grades and the skin severity scores showed the same tendency as recorded in the last 10 years. Yusho patients who were scored as more than 6.7 were around 8% of the total patients both in 1995 and 1996. The correlation between the blood PCB patterns and the severity grades of skin symptoms was clear. Thus, the mean skin severity scores in patients showing A pattern were higher than those in patients showing either B or C pattern. The same results were obtained when the correlation between the blood PCB patterns and the skin severity grades was analyzed. Patients whose ages were 50-70 years old were found to show the highest blood PCB concentrations and the skin severity scores.

We reported the grades of severity of skin symptoms and the blood PCB patterns and concentrations in Yusho patients who were examined in the annual examinations in 1993 and 1994. The skin severity grades and skin severity scores showed the same tendency as recorded in the last 15 years. Approximately 20% of the patients, however, claimed the tendency of recurrence of skin infections and/or infected epidermal cysts, and still approximately 30% of the patients exhibited acneiform eruptions. Ten patients recorded with more than 6 points of skin severity scoring in these examinations were further investigated their initial skin severity grades and blood PCB patterns and concentrations. It was found that most of their blood PCB patterns showed the A pattern, and the level of the blood PCB in one patient was 55.5 ppb in the initial stage. Five patients out of 10 patients still have more than 10 ppb of blood PCB concentration. Thus, it is concluded that small populations of Yusho patients still have active skin symptoms with considerable blood PCB levels even at present.

The occurrence and progress of Yusho (PCB mass poisoning) is briefly described. Various investigative studies on Yusho are also briefly reviewed. Yusho occurred in the northern district of Kyushu Island in 1968. A specific product of rice oil used for food was accidentally contaminated with PCB during its manufacturing process and consequently, the customers who ate it showed severe intoxication symptoms. Major clinical symptoms of Yusho were acneiform eruptions and circumscribed pigmentation. These skin and mucous membrane eruptions, because of their appearance, caused severe mental suffering for the patients. The government-authorized patients amounted to 1,860. These symptoms have gradually declined with the passing of years and presently the principal clinical problems are only various subjective complaints. At first, it was naturally thought that the causative agent of Yusho was PCB (Kanechlor 400) itself. However, it was found later that the causative rice oil contained PCDF (polychlorodibenzofuran) and PCQ (polychloroquaterphenyl) which were proved to be formed during the heating process used in the deodorization of the oil. PCDFs show, in animal studies, a high toxicity and therefore its role for the pathogenesis of Yusho is seriously evaluated in spite of its rather small contaminating amount. On the other hand, PCQs are recognized as the specific marker of Yusho, since almost no PCQ is a general environmental pollution substance.

We reported on the skin symptoms of the patients with yusho in the 1987 and 1988 annual examinations. We also studied the alteration of the skin symptoms in the patients followed up for 20 years. These patients showed obvious improvement in their skin symptoms during these 20 years. However, about a half of the patients still had comedones and/or acneiform eruptions, although the number of eruptions had decreased. The cases with blood PCB pattern A (typical yusho pattern) demonstrated higher skin severity grading points than those of the other groups (patterns B and C), but even in these cases the skin eruptions had improved.

Skin symptoms of "yusho" and their change thereafter are described. In the early stage, skin eruptions were the most prominent and impressive features of yusho. Acneiform eruptions and pigmentation were most conspicuous. With the passage of time, there is some improvement and most patients now have few eruptions, except for the severely intoxicated group. As for blood PCB analysis, the severely intoxicated group who showed intensive skin symptoms showed "pattern A"--a typical specific yusho pattern. The blood PCB patterns of each patient were stable with no alteration after many years and, on the other hand, the blood PCB concentrations have diminished year by year.