Pseudoxanthomatous lesions with membranocystic changes of collagen fibers in an SLE patient receiving long-term steroid treatment

We report a 50-year-old Japanese woman with a 3-year history of systemic lupus erythematosus treated with prednisolone, who had diffuse plane yellowish macules mainly on the upper arm. The lesion was clinically diagnosed as diffuse plane xanthomatosis. However, the histopathological findings from both the yellowish macules and the normal-appearing skin revealed a heavy degeneration of collagen fibers with membranocystic structure throughout the entire dermis and the collagenous septum of the subcutaneous tissue. Ultrastructurally, the membranocystic structure was not due to the degenerative change of fat cells as seen in membranous lipodystrophy but was caused by the degenerative change of collagen fibers with fat deposit.