During a medicolegal autopsy, the pathologist observes that rigor mortis is completely absent despite the body being found 24 hours after death. Which of the following is the most common cause of absent rigor mortis in this scenario?

Explanation

## Absent Rigor Mortis: Causes and Forensic Significance **Key Point:** Rigor mortis is a temporary phenomenon that eventually disappears. The most common cause of absent rigor mortis at 24 hours is **advanced decomposition**, which masks or destroys the rigor through bacterial putrefaction and tissue breakdown. ### Why Rigor Mortis Disappears 1. **Decomposition timeline:** Rigor typically lasts 24–48 hours in normal conditions. 2. **Putrefaction:** Bacterial enzymes break down muscle proteins and myosin-actin complexes. 3. **Tissue disintegration:** Advanced decomposition physically disrupts muscle structure. 4. **Masking:** Bloating and tissue gas accumulation obscure the stiffness. **High-Yield:** At 24 hours postmortem, if rigor is absent, decomposition is the **most common cause** in typical environmental conditions (room temperature, normal humidity). ### Conditions Affecting Rigor Mortis Presence | Condition | Effect on Rigor | Mechanism | |-----------|-----------------|----------| | **Advanced decomposition** | Absent (masked/destroyed) | Bacterial putrefaction breaks down muscle proteins | | **Extreme cold** | Preserved (delayed onset) | Low temperature slows ATP depletion and decomposition | | **Cachexia/starvation** | Delayed/weak | Minimal muscle mass, slow ATP depletion | | **Septicemia/fever** | Accelerated onset | Rapid metabolism and muscle exertion | **Clinical Pearl:** In forensic pathology, **absence of rigor at 24 hours is NOT suspicious** — it is the expected natural progression. Rigor is temporary and is replaced by decomposition changes. **Mnemonic:** **"Rigor Comes and Goes"** — rigor mortis is a transient sign, present 2–48 hours, then masked by putrefaction. ### Forensic Interpretation - **Rigor present at 24 hours:** Suggests cold environment or delayed decomposition. - **Rigor absent at 24 hours:** Normal progression; indicates decomposition has begun. - **Never use rigor alone for time-of-death estimation** — combine with algor mortis, livor mortis, and decomposition stage.