Viper envenoming — DTM&H MCQ

Correct answer: E — Viper envenoming with coagulopathy

A) Viper envenoming with coagulopathy is correct because the combination of painful local swelling, a whole blood clotting test that remains unclotted at 20 minutes, and spontaneous gum bleeding is the classic syndrome of venom-induced consumption coagulopathy (VICC) following Russell's viper (Daboia russelii) bite, the commonest cause of medically significant envenoming in Sri Lanka. WHO regional guidelines identify the 20 minute whole blood clotting test (20WBCT) as the key bedside tool for detecting incoagulable blood, and a positive test with systemic bleeding (gums, venepuncture sites) confirms systemic envenoming requiring urgent antivenom. Painful progressive local swelling at the bite site is typical of viperid (as opposed to elapid) venom, which contains procoagulant toxins that deplete fibrinogen and clotting factors. This clinical and laboratory picture is pathognomonic enough in this geography to make viper envenoming the most likely diagnosis without further testing. Why the other options are wrong: B) Krait bite: Kraits (elapids) cause descending flaccid paralysis (ptosis, bulbar weakness, respiratory failure) with minimal local swelling and no coagulopathy, so painful swelling plus incoagulable blood is inconsistent. C) Allergic urticaria: This causes itchy wheals and possible anaphylaxis but does not cause painful tissue swelling, prolonged whole blood clotting time, or spontaneous mucosal bleeding. A. Scorpion sting: Scorpion envenoming produces intense local pain, autonomic storm and occasionally cardiotoxicity, but does not derange the coagulation system or cause gum bleeding. D. Tetanus: Tetanus presents with trismus, muscle rigidity and spasms after a contaminated wound, days after injury, with normal clotting and no bleeding tendency. Key point: Painful local swelling plus a positive 20 minute whole blood clotting test with spontaneous bleeding after snakebite in Sri Lanka is diagnostic of viper (Russell's viper) venom-induced coagulopathy and mandates antivenom.

Reference: WHO Regional Office for South-East Asia, Guidelines for the Management of Snakebites, 2nd edition (2016), Section 4.5 Investigations/laboratory tests (20 minute whole blood clotting test)