A child with recurrent pyogenic arthritis with the PSTPIP1 mutation.

Pyogenic arthritis, pyoderma gangrenosum, and acne syndrome is a rare disease, linked to an auto-inflammatory pathway. We report a 7-year-old boy with recurrent suppurative knee arthritis without signs of suppurative skin infection or ulcer; his younger brother had the same symptom. Genetic testing indicated the presence of proline-serine-threonine phosphatase interacting protein 1 gene mutation in both boys. Our patient's grandfather had a history of recurrent pyoderma, and his father though a genetic carrier had no symptoms. Interestingly, our patient displayed markedly high levels of interleukin-6, while interleukin-1 and other cytokines were not elevated. These lab findings led to the treatment of pyogenic arthritis, pyoderma gangrenosum, and acne syndrome with tocilizumab. Previously reported cases of similar phenotypes of the syndrome have not presented in this fashion, nor have there been reported cases of pyogenic arthritis, pyoderma gangrenosum, and acne syndrome with a positive family history and an elevation in interleukin-6. The mutation site of proline-serine-threonine phosphatase interacting protein 1 in this incomplete pyogenic arthritis, pyoderma gangrenosum, and acne syndrome has not been reported before. It is possible that there are other pathogenic ways to trigger these auto-inflammatory disorders. Tocilizumab, which specifically targets interleukin-6, was effective in this case.