Which feature best distinguishes rigor mortis from cadaveric spasm in a body recovered from a fire scene?

## Distinguishing Rigor Mortis from Cadaveric Spasm ### Timing: The Critical Discriminator **Key Point:** Cadaveric spasm occurs **instantaneously at the moment of death** (or within seconds), whereas rigor mortis is a **post-mortem phenomenon** that develops **2–6 hours after death** and progresses over 24–48 hours. ### Pathophysiology | Feature | Rigor Mortis | Cadaveric Spasm | |---------|-------------|----------------| | **Onset** | 2–6 hours post-mortem | Instantaneous (at/before death) | | **Mechanism** | ATP depletion → actin-myosin cross-link rigidity | Intense muscle contraction from CNS discharge (violent death, electrocution, fire) | | **Distribution** | Generalized (all muscles) | Localized (single muscle groups) | | **Reversibility with heat** | Reversible (muscle proteins denature at 65°C) | Irreversible (already contracted before heating) | | **Appearance** | Gradual stiffening | Sudden flexion/extension posture | | **Forensic significance** | Helps estimate time of death | Indicates violent circumstances; NOT evidence of antemortem struggle | ### Clinical Pearl **High-Yield:** In fire deaths, cadaveric spasm can mimic a "pugilistic attitude" (boxer's stance), but this is **not** evidence the victim was conscious or fighting — it is a post-mortem artifact from heat-induced muscle contraction. True rigor mortis would develop *after* this spasm. ### Why Timing Matters in Forensics **Mnemonic: RIGOR-T** — **R**igidity **I**s **G**radual **O**nset **R**elated to **T**ime (hours post-mortem) Cadaveric spasm is instantaneous; rigor mortis is delayed. This distinction is crucial for: - Differentiating antemortem (before death) from post-mortem phenomena - Excluding cadaveric spasm as evidence of struggle - Estimating post-mortem interval **Warning:** Do not confuse cadaveric spasm with rigor mortis. Cadaveric spasm is a **single, violent contraction** at death; rigor mortis is a **progressive stiffening** hours later.