Histopathologic Characterization of Cutaneous Oxalosis Mimicking Calciphylaxis: Diagnostic Pitfalls and Polarized Light Evaluation

Cutaneous oxalosis is an uncommon manifestation of primary hyperoxalosis, which can often resemble other cutaneous manifestations of end stage renal disease (ESRD), particularly calciphylaxis. We report the case of a 46 year old female with primary hyperoxaluria type one (PH1) believed to be well‐controlled on lumasiran, a small interfering ribonucleic acid therapy, which targets the mRNA responsible for producing hydroxyacid oxidase 1 (HAO1) and through reduction of this enzyme, decreases the hepatic overproduction of oxalate. The patient presented for dermatologic evaluation of presumed calciphylaxis. Repeated skin biopsies, however, confirmed cutaneous oxalosis despite perceived stable metabolic control with lumasiran. This case highlights the complexities and challenges in the diagnosis of cutaneous manifestations of chronic kidney disease and emphasizes the importance of histopathologic evaluation, even if the patient's primary hyperoxaluria is believed to be well‐controlled.