Tacrolimus-induced asymptomatic thrombotic microangiopathy diagnosed by laboratory tests in pig-to-rhesus corneal xenotransplantation: A case report

: Tacrolimus-associated thrombotic microangiopathy (TA-TMA) is a rare complication. TA-TMA is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and organ damage due to thrombus. We report asymptomatic TA-TMA diagnosed by laboratory tests in pig-to-rhesus corneal xenotransplantation. Corneal transplantation had been conducted from a wild-type SNU miniature pig to a rhesus macaque. The veterinary records were retrospectively reviewed in this case. The immunosuppressive regimen consisted of rituximab, basiliximab, and IVIg as inductive therapies, and steroids with tacrolimus (0.1 mg/kg/day) as maintenance therapies. Although there were no clinical symptoms, increased levels of lactate dehydrogenase, total bilirubin, blood urea nitrogen, and creatinine and decreased levels of hemoglobin and platelet were observed in laboratory tests on Day (D) 61. Systemic TA-TMA was tentatively diagnosed. Tacrolimus was discontinued starting on D71. Dalteparin, clopidogrel bisulfate (D77-D99), and IVIg (D72) were administered as a conservative treatment. Abnormal laboratory results were reversed on D99. When low-dose tacrolimus (0.07 mg/kg/day) was re-administered on D131 to prevent rejection of the graft, TMA was detected again by laboratory tests on D161, confirming the initial diagnosis. Discontinuation of tacrolimus on D162 and re-administration of Dalteparin (D161-D196) corrected the laboratory values on D161. This report shows that in pig-to-rhesus corneal xenotransplantation, clinically asymptomatic TMA can be induced by tacrolimus, and the discontinuation of tacrolimus and administration of anticoagulant seems sufficient to correct the laboratory TMA.