A laboratory worker ingests oxalic acid in a suicide attempt. She develops oral burns, abdominal pain, and carpopedal spasm with positive Chvostek and Trousseau signs. Urinalysis shows abundant envelope-shaped crystals. The tetany results from:
- A Direct stimulation of peripheral nerves by absorbed oxalate
- B Fall in ionised serum calcium due to formation of insoluble calcium oxalate ✓
- C Renal tubular acidosis causing hypokalaemia
- D Oxalate-induced release of acetylcholine at the neuromuscular junction
Correct answer: B. Fall in ionised serum calcium due to formation of insoluble calcium oxalate
Explanation
Oxalic acid combines avidly with calcium to form insoluble calcium oxalate. This precipitates as envelope-shaped (dumbbell or octahedral) crystals in the urine and deposits in renal tubules, causing acute kidney injury, while the depletion of circulating ionised calcium produces tetany, carpopedal spasm, and positive Chvostek and Trousseau signs. Hypocalcaemia may be severe enough to cause cardiac arrest from systolic standstill.
Reference: Parikh's Textbook of Medical Jurisprudence, Forensic Medicine and Toxicology, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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