Acquired haemophilia B in Kyasanur Forest disease: a case series of isolated prolonged activated partial thromboplastin time.
Nitin Gupta, Sushma Belurkar, Muralidhar Varma et al.
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Case in brief
Nine patients with confirmed acute Kyasanur Forest disease had prolonged activated partial thromboplastin time (APTT) with normal prothrombin time. Ages ranged from 29 to 78 years; one patient had epistaxis, while the others had no evident bleeding. APTT ranged from 37.0 to 74.8 s. Mixing studies and factor assays indicated reduced factor IX activity (24.0% to 48.4%) with preserved or elevated factor VIII. Inhibitor screening was negative in the two patients tested. APTT normalized in all patients on follow-up; factor IX activity returned to the reference range in seven of the eight patients retested.
What made this case unusual
The isolated APTT prolongation was associated with transient acquired factor IX deficiency, rather than a generalized coagulation abnormality; most patients had no clinically evident bleeding.
Diagnostic / clinical pearl
In acute Kyasanur Forest disease, isolated prolonged APTT with normal PT should prompt consideration of factor IX deficiency; mixing studies and factor assays can help identify this pattern.
Why it matters
Recognizing selective intrinsic pathway dysfunction may help distinguish this pattern from disseminated intravascular coagulation and inform coagulation support in severe disease.