Background Pustulotic arthro‐osteitis (PAO) is a major comorbidity of palmoplantar pustulosis (PPP), which is frequently seen in Japanese patients. To determine the characteristics of Japanese patients with PAO, we conducted a multicenter, retrospective epidemiologic survey at four university hospitals. Methods Clinical features including age, gender, duration of disease, extrapalmoplantar lesion, smoking habit, focal infection, site of joint pain, bone scintigraphy with Technetium99, and therapies were retrospectively evaluated. Results In total, 165 patients with PAO were identified among 576 patients with PPP (28.6%). The male to female ratio was 1 : 3.7, and the mean age was 50.2 years. The mean disease duration of PAO was 6.0 years. Smoking habit was observed in 104 patients. Focal infection was detected in 74 patients, who developed tonsillar infection (n = 41), sinusitis (8), odontogenic infection (40), and others (2). Fifteen patients had multifocal infection. Technetium bone scintigraphy was performed in 97 cases. Increased uptake was most frequently observed in the sternocostoclavicular regions, followed by wrist and ankle, sacroiliac joint, knee and elbow, finger and toe, lumbar spine, thoracic spine, scapula, and thigh. Patients were mainly treated with nonsteroidal anti‐inflammatory drugs, methotrexate, cyclosporine, antibiotics, and biologics, as well as tonsillectomy and dental treatment. Conclusion PAO frequently involves the anterior chest wall of middle‐aged women with smoking habit and is closely associated with focal infection.

Palmoplantar pustulosis (PPP) and pompholyx are both chronic and relapsing diseases occurring on the palms and soles. Although these two diseases have been considered completely different from each other, it is sometimes very difficult even for dermatologists to differentiate them from each other because of their similarities in clinical presentation. In this study, we aimed to analyze the histopathological features of PPP and pompholyx and find out “clues” to differentiate between PPP and pompholyx by their histopathological features. The histopathology of 11 PPP and six pompholyx patients, who were diagnosed with typical clinical history and histopathology, were carefully observed. PPP cases were divided into three phases (vesicle, pustulovesicule and pustule) and pompholyx cases were divided into two phases (vesicle and pustule), and histopathological findings and a 4‐point checklist to distinguish between PPP and pompholyx were preliminarily established. To confirm whether the checklist establishes the clues for diagnosis, biopsy samples from 43 patients (32 PPP and 11 pompholyx) who had been already diagnosed at five hospitals were examined according to our checklist without any additional clinical information. According to our 4‐point checklist, 31 of 32 PPP patients and all 11 pompholyx patients were diagnosed histopathologically consistent with their clinical diagnosis. In conclusion, histopathological findings of “vesicles without spongiosis” and “microabscess on the edges of vesicles” would be impact points for the differential diagnosis between PPP and pompholyx. The 4‐point checklist was trustworthy to distinguish between PPP and pompholyx.

The skin microbiome influences skin pathophysiology. Palmoplantar pustulosis (PPP) is a chronic skin disease characterized by infectious‐like pustules on the palms and soles. These pustules are thought to be sterile because bacterial cultures obtained from the pustules are negative. However, culture methods are limited in their ability to identify all bacteria on the skin. We hypothesized that the “sterile” pustules of PPP do not lack bacteria, but rather contain a microbiome. To test this hypothesis, we identified bacteria in “sterile” pustules using non‐culture methods. We conducted Sanger and 16S rRNA sequencing using primers specific to the V1‐V2 region in PPP‐pustulovesicles (PVs) (n = 43) and pompholyx vesicle fluids (n = 15). Sanger sequencing identified some Staphylococcus, Propionibacterium, Streptococcus and Pyrinomonas species in PPP‐PVs but failed to identify any bacteria in most of the pompholyx vesicles. 16S rRNA sequencing of PPP‐PVs indicated the presence of a microbiome that included various phyla, including Firmicutes, Proteobacteria, Actinobacteria and Bacteroidetes. At the genus level, smokers had higher levels of Staphylococcus in PPP‐PVs compared with non‐smokers. These results indicate that a microbiome exists in “sterile” pustules of PPP and that PPP smokers had higher levels of Staphylococcus in pustules. It is therefore necessary to reconsider the pathogenesis of PPP from the perspective of the microbiome.

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