## Characteristic Features of Cyanide Poisoning **Key Point:** The **bitter almond odour** is the pathognomonic smell associated with cyanide poisoning, though it is not always detected and its absence does not rule out cyanide poisoning. ### Clinical and Forensic Features #### Odour Characteristics - **Bitter almond smell** — Caused by hydrogen cyanide (HCN) gas released during decomposition or from gastric contents - **Genetic variation** — Approximately 40–50% of the population can detect this odour; the remainder are anosmic to it - **Reliability** — Not a reliable diagnostic feature, as the odour may be absent or masked by other decomposition odours #### Other Characteristic Findings in Cyanide Poisoning | Feature | Mechanism | Clinical Significance | |---------|-----------|----------------------| | **Pink or cherry-red lividity** | Venous blood remains oxygenated due to inability of tissues to extract O₂ | Rare but characteristic | | **Rapid onset of death** | Histotoxic hypoxia affects high-demand organs (brain, heart) | Death within minutes | | **Absence of rigor mortis** | Rapid depletion of ATP prevents muscle contraction | Forensic clue | | **Convulsions** | Cerebral hypoxia from blocked aerobic metabolism | Perimortem sign | | **Bitter almond odour** | HCN gas release | Forensic clue (not always present) | **High-Yield:** The **pink or cherry-red discolouration** of tissues and blood is more specific than the odour, as it reflects the failure of tissues to extract oxygen from blood despite its presence. **Warning:** Do NOT rely solely on odour for diagnosis. Many decomposed bodies may not emit the characteristic smell, and the odour may be masked by putrefaction. Toxicological analysis is essential for confirmation. **Mnemonic:** **CHOP** — **C**yanide causes **H**istotoxic hypoxia, **O**dour (bitter almond), **P**ink/cherry-red lividity.
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