Regarding rigor mortis, all of the following statements are correct EXCEPT:

Question

Accepted Answer

C. Rigor mortis typically appears within 2–3 hours of death and is completely resolved by 48–72 hours in all environmental conditions. ## Rigor Mortis: Onset, Progression, and Resolution

### Definition and Mechanism
**Key Point:** Rigor mortis is a post-mortem stiffening of muscles caused by depletion of adenosine triphosphate (ATP) and accumulation of lactic acid, leading to permanent cross-linking of actin and myosin filaments.

### Onset and Progression
**High-Yield:** Rigor mortis typically begins in the eyelids, muscles of mastication, and neck, then progresses in a cephalocaudal (downward) direction to the trunk and limbs. This pattern is consistent and predictable.

### Timeline and Factors Affecting Onset
| Factor | Effect on Rigor Mortis |
| --- | --- |
| Normal conditions | Appears 2–3 hours post-mortem |
| Heat/high temperature | Accelerates onset (heat accelerates enzyme activity) |
| Cold/low temperature | Delays onset |
| Prolonged illness/starvation | Delayed onset (reduced muscle glycogen) |
| Cachexia | Delayed or absent rigor |
| Muscular exertion before death | May appear earlier |

### Resolution Timeline
**Warning:** The statement that rigor mortis is "completely resolved by 48–72 hours in all environmental conditions" is **INCORRECT**. Resolution depends heavily on environmental factors:
- In cool environments: rigor may persist for 8–10 days or longer
- In warm/hot environments: rigor resolves faster (3–5 days) due to bacterial decomposition and muscle autolysis
- In cold storage (refrigeration): rigor may persist indefinitely until thawing occurs

**Clinical Pearl:** The absence of rigor mortis does not mean death occurred recently — it may indicate advanced decomposition, extreme environmental conditions, or conditions that prevent rigor formation (cachexia, prolonged illness).

### Why Each Statement Is Evaluated
1. **Cephalocaudal progression** — TRUE; this is the classic pattern taught in all forensic medicine texts
2. **Delayed onset in illness/starvation** — TRUE; reduced muscle glycogen delays rigor formation
3. **ATP depletion and actin-myosin cross-linking** — TRUE; this is the biochemical mechanism
4. **Complete resolution by 48–72 hours in all conditions** — FALSE; resolution is highly variable and depends on temperature, humidity, and decomposition rate

Answer

A. The onset of rigor mortis is delayed in cases of prolonged illness, starvation, and cachexia

Answer

B. Rigor mortis begins in the eyelids and muscles of mastication and progresses downward in a cephalocaudal direction

Answer

D. Rigor mortis is caused by cross-linking of actin and myosin filaments due to depletion of ATP and accumulation of lactic acid

Regarding rigor mortis, all of the following statements are correct EXCEPT:

Explanation

Rigor Mortis: Onset, Progression, and Resolution

Definition and Mechanism

Onset and Progression

Timeline and Factors Affecting Onset

Resolution Timeline

Why Each Statement Is Evaluated

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Factor	Effect on Rigor Mortis
Normal conditions	Appears 2–3 hours post-mortem
Heat/high temperature	Accelerates onset (heat accelerates enzyme activity)
Cold/low temperature	Delays onset
Prolonged illness/starvation	Delayed onset (reduced muscle glycogen)
Cachexia	Delayed or absent rigor
Muscular exertion before death	May appear earlier