Bee sting Factor V inhibition baffles haematologists

Haematologists in NSW have been puzzled by profound prolongation of clotting times seen in a young man with anaphylactic shock following a bee sting.

The incident, in which the man died, may be a rare case of a ‘perfect storm’ caused by an unidentified bee venom Factor V inhibitor and other contributing factors, according to haematologist Dr Emmanuel Favaloro and colleagues at Westmead Hospital.

In their report, published in the American Journal of Hematology, they describe how the 25 year old male developed anaphylaxis after being stung on the lip by a bee while gardening at home in Sydney.

In addition to the several symptoms of anaphylaxis, clinicians at the hospital ICU were surprised to find profound derangement of haemostasis tests including prothrombin time of (>120 seconds), activated partial thromboplastin time (>150s) and very low fibrinogen levels (<0.6g/L).

The patient developed haematuria and haematochezia and was also issued 4 units of fresh frozen plasma and 2 units of cryoprecipitate  for the management of presumptive disseminated intravascular coagulopathy (DIC). However further heparin and factor assays made it clear that the primary differential diagnosis of DIC was unlikely to be the sole cause of the prolonged clotting times.

An abnormal mix-APTT test and a global reduction in factor levels, with undetectable V, VIII, IX and XI made it probable that some sort of factor ‘inhibitor’ was at play.

Another unusual finding was that the Factor V-like inhibition was time dependent, with normalisation of haemostasis after about 20 hours. While further plasma product was given the patient was pronounced brain dead after 40 hours.

Dr Favaloro and pathologist Dr Elisabeth Farhat speculate that the coagulation abnormality may have been caused by some kind of Factor-V like inhibitor related to phospholipase A2 component of bee venom.

“Also with the benefit of informed hindsight, it is similarly possible that the released tryptase itself … may potentially have contributed to deranging haemostasis by direct effects on fibrinogenolysis and the fibrinolytic pathway,” they write.

“The derangement in haemostasis we observed was possibly further complicated by a DIC-like event, in particular given the positive D-dimer ,” they add.

The case highlights the need for further evaluation of the haemostatic abnormalities that occur with insect sting venoms, they conclude.

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