Thrombotic microangiopathy (TMA) with microangiopathic haemolytic anaemia (MAHA), thrombocytopenia and severe renal impairment has been described in a case report of an Australian snake handler bitten on the hand by a tiger snake.
The Geelong case, published in Nephrology [link here], represents only the fourth known documented case of TMA associated with tiger snake envenomation in Australia.
The report said rapid administration of antivenom, ideally within two hours of the bite, is key to minimising severe systemic envenomation and organ dysfunction.
However in this case, the time from bite to receipt of anti-venom was 3.5 hours. The delay was partly due to a medical decision to wait for laboratory evidence of coagulopathy to confirm systemic envenomation.
Initial tests found established venom-induced consumptive coagulopathy (VICC) with prothrombin time 27.5 s (normal range 9–13), activated partial thromboplastin time (apTT) 45 s (normal 23-35), international normalised ratio (INR) 1.8 (normal 0.8–1.2), fibrinogen 0.7 g/L (normal 2.0–4.0) and platelets 136 x 109/L (normal 150–400).
Renal and liver function were within normal limits.
However, eight hours post-envenomation the patient showed signs of TMA with MAHA and acute severe renal impairment.
Laboratory findings included platelets 103 x 109/L, LDH 9270 U/L (normal 50–280), haptoglobin 0.12 g/L (normal 0.4–2.4), creatinine 318 mol/L, eGFR 18 mL/min/1.73 m2, urinary protein excretion 1223 mg/mmol (normal <21) and numerous schistocytes on blood film.
The patient was admitted to the intensive care unit and commenced renal replacement therapy with continuous venovenous haemofiltration.
Laboratory features of TMA steadily worsened and there was no improvement in his renal function.
“A renal perfusion study showed reduced tracer uptake and perfusion with poor clearance, consistent with acute tubular necrosis…” the case report said.
The patient remained on haemofiltration with a nadir haemoglobin of 63 g/dL and platelet count of 12 x 10 9/L on day 6 of admission.
“Due to persistent severe renal failure, daily plasma exchanges (of 1.3 times total plasma volume using 1.5 L of thawed fresh frozen plasma) were undertaken from day 6 to day 10 inclusive and ceased when ADAMTS13 activity was shown to be normal at 98%, and the platelet count and LDH had normalised.”
The patients was transferred to a ward on day six and switched from continuous venovenous haemofiltration to intermittent haemodialysis administered for 4 hours, three times a week.
“Despite heparin anticoagulation during dialysis sessions, frequent thrombi were seen in the dialysis circuitry suggesting an ongoing prothrombotic state, though no systemic thrombosis was clinically evident.”
The patients was discharged after 2 weeks in hospital with ongoing outpatient haemodialysis 3 days a week.
“Haemodialysis was ceased 8 weeks after the snakebite due to improvement in renal function with creatinine 92 μmol/L and eGFR 83 mL/min/1.73 m2 at this time.”
The patient was followed up through the renal outpatient clinic and at last review, three years post snakebite, his renal function had returned to baseline.
The authors of the case report said antivenom should be given as soon as possible for any patient with signs of systemic envenomation.
“Traditionally, a desire to avoid unnecessary administration of antivenom, with attendant risk of anaphylaxis, has led to the practice of waiting for demonstrated coagulopathy before administering antivenom,” they said.
However the case showed unnecessary delays can lead to an increased risk of complications.
“On review there were already other, albeit less specific, signs of systemic envenomation (nausea, abdominal pain) on arrival at hospital and faster administration of antivenom may have mitigated the severity of his renal injury.”