The key difference between rigor mortis and cadaveric spasm is that rigor mortis occurs in all types of muscles gradually while cadaveric spasm occurs only in the group of voluntary muscles which were in a state of contraction at the time of death.
There are certain changes occurring in the body after death. Some changes are related to somatic death, while some are related to molecular death. There are certain changes that occur immediately at the moment of death; for example, the stopping of the nervous system, respiration and circulation, etc. Some changes occur as early as possible while some take place later. Cooling of the body, change in the eye colour, loss of the elasticity of the skin, and facial pallor are some of the early changes after death.
Rigor mortis and cadaveric spasm are two post mortem changes. Rigor mortis is the postmortem stiffening of the body muscles. It begins 2 to 3 hours after death and goes up to 24 hours. Cadaveric spasm is a rare form of muscle stiffening that occurs at the moment of death. Cadaveric spasm is often associated with extreme nervous stimulation or violent death.
CONTENTS
1. Overview and Key Difference
2. What is Rigor Mortis
3. What is Cadaveric Spasm
4. Similarities Between Rigor Mortis and Cadaveric Spasm
5. Side by Side Comparison – Rigor Mortis vs Cadaveric Spasm in Tabular Form
6. Summary
What is Rigor Mortis?
Rigor mortis is the stiffening of the body muscles after death. It is also known as cadaveric rigidity. In rigor mortis, muscles become stiff or rigid with some degree of shortening. All types of muscles are affected gradually. Rigor mortis begins after 1 to 2 hours of death. It persists for up to 24 hours. It is a type of physiochemical process. It takes place as a result of the breakdown of ATP below a critical level (depletion of body energy). Muscle fibers need ATP for contraction and relaxation.
Figure 01: Skeletal Muscle Contraction
When ATP is not there, actin and myosin protein remain compressed, resulting in muscle stiffness. Rigor mortis develops in heart muscles initially. Then it appears in the muscles of the eyelid, face, neck, jaw, thorax, abdomen, lower limb, etc. Finally, it occurs in the small muscles of fingers.
Rigor mortis is a sign of death. Moreover, it reveals the time since death. In addition, it is important to determine the position of the body and whether it has been moved after the development of rigor mortis.
What is Cadaveric Spasm?
Cadaveric spasm, also known as instantaneous rigor, is a condition of muscles continuing to be more contracted at the moment of death and after death without undergoing primary relaxation. Therefore, it takes place in a selected group of muscles, especially a group of voluntary muscles which were in a state of contraction at the time of death. It is a rare form of rigor. Cadaveric spasm begins at the moment of death and continues until it is replaced by rigor mortis.
The reason for cadaveric spasm is unknown. However, it is usually associated with a violent death happening with intense emotions due to extreme nervous stimulation. Cadaveric spasm is seen in dead bodies of victims of drowning. Generally, the dead body demonstrates the last activity that person did prior to death. Hence, cadaveric spasm is useful information in forensic investigations.
What are the Similarities Between Rigor Mortis and Cadaveric Spasm?
- Rigor mortis and cadaveric spasm are two differential diagnoses of stiffening of a dead body.
- Both are postmortem changes that reveal important information regarding the death.
- Cadaveric spasm is replaced by rigor mortis.
- Cadaveric spasm can be mistaken as rigor mortis.
- In both cases, stiffening of muscles takes place.
What is the Difference Between Rigor Mortis and Cadaveric Spasm?
Rigor mortis is the stiffening of all types of muscles after 2 to 3 hours of death while cadaveric spasm is a rare form of rigor that occurs at the time of death due to extreme nervous stimulation. So, this is the key difference between rigor mortis and cadaveric spasm. Rigor mortis occurs after 2 to 3 hours of death while cadaveric spasm occurs at the time of death. Both rigor mortis and cadaveric spasm are important information for forensic investigations. Rigor mortis reveals the time since death and position of the dead body while cadaveric spasm demonstrates the last activity prior to death.
The below infographic tabulates more comparisons related to the difference between rigor mortis and cadaveric spasm.
Summary – Rigor Mortis vs Cadaveric Spasm
Rigor mortis and cadaveric spasm are two types of postmortem changes. Rigor mortis is the stiffening of body muscles due to chemical changes in their myofibrils. Cadaveric spasm, on the other hand, is a rare form of rigor that happens due to extreme nervous stimulation at the time of death. Generally, cadaveric spasm occurs at death and continues until it is replaced by rigor mortis. Rigor mortis begins after 2 to 3 hours of death and lasts for up to 24 hours. Moreover, rigor mortis happens in all types of muscles, while cadaveric spasm occurs only in a selected group of muscles. Thus, this summarizes the difference between rigor mortis and cadaveric spasm.
Reference:
1. “Death & Changes After Death”. Slideshare.Net, 2020, Available here.
2. “Cadaveric Spasm”. En.Wikipedia.Org, 2020, Available here.
Image Courtesy:
1. “1008 Skeletal Muscle Contraction” By OpenStax – (CC BY 4.0) via Commons Wikimedia