• Sheng-Chieh Chou, Ching-Yeh Lin, Ching-Tzu Yen, Han-Ni Hsieh, Ying-Chih Huang, Ko-Jen Li, Shu-Wha Lin, and Ming-Ching Shen.
• Department of Internal Medicine, Division of Hematology, National Taiwan University Hospital, Taipei, Taiwan. Electronic address: choushengchieh@ntuh.gov.tw.
• J Formos Med Assoc. 2021 Jan 1; 120 (1 Pt 2): 411-414.

IntroductionAcquired factor XIII (FXIII) inhibitor is a rare but possibly underdiagnosed bleeding disorder. To date, less than one hundred cases have been reported, but the number has increased rapidly in recent years, especially in Japan. Because of the rarity of this disorder, no treatment guidelines are available. In some reports, physicians treated the bleeding with cryoprecipitate or factor XIII concentrate and eradicated the inhibitor with various immune suppressants.MethodsFrom January 2015 to December 2018, we collected consecutive patients diagnosed as having acquired FXIII inhibitor. FXIII activity and inhibitor were measured by a fluorescent factor XIII assay using isopeptidase reaction catalyzed by activated factor XIII and the Bethesda method, respectively. Factor XIII antigen was measured by latex-enhanced immunoassay.ResultsWe found five adult patients with detectable FXIII inhibitor. Four of them were older than 70. Two had systemic lupus erythematosus. All the patients presented with ecchymosis and intramuscular hematoma. No life-threatening bleeding was observed. Delayed diagnosis was common with varied time periods needed to achieve a correct diagnosis. All bleedings were treated and improved by cryoprecipitate. Steroids were given to all patients and cyclophosphamide, rituximab, and other immune suppressants were also used. FXIII inhibitor was totally resolved in three, partially resolved in one, and persisted in one patient.ConclusionWe documented five patients with acquired FXIII inhibitor, found over 4 years. The most common presentations were ecchymosis and intramuscular hematomas. Cryoprecipitate was effective in controlling most bleeds. Steroid, cyclophosphamide and rituximab were effective in eradicating inhibitor in some patients.Copyright © 2020 Formosan Medical Association. Published by Elsevier B.V. All rights reserved.

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