Post mortem changes

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Post Mortem Changes

Post mortem changes are the physical, chemical and biological changes that occur in a body after death. They are used in forensic medicine to estimate the post mortem interval (PMI) and to determine circumstances of death. They are divided into early (primary) and late (secondary) changes.

Classification

Category	Changes
Early / Primary	Algor mortis, Livor mortis (PM hypostasis), Rigor mortis, Autolysis
Late / Secondary	Putrefaction, Adipocere, Mummification, Maceration, Skeletonization

I. ALGOR MORTIS (Cooling of the Body)

After death, metabolic heat production ceases. The body loses heat by conduction, convection, radiation, and evaporation until it reaches ambient temperature. This is also called dead body chill.

Cooling Pattern

For the first ~30 min to 1 hour, temperature falls little or not at all - this is the isothermic phase (postmortem temperature plateau)
Then falls in a sigmoid (S-shaped) curve - initial slow fall, rapid fall, then slow approach to ambient
Rule of thumb (temperate): ~1°C per hour in the rectum; in tropical climates 0.4-0.6°C per hour
Rectal temperature is the most reliable site for measurement

Factors Affecting Rate of Cooling

Factor	Faster Cooling	Slower Cooling
Body build	Thin, children, elderly	Fat, obese
Clothing	Absent	Heavy clothing
Environment	Well-ventilated, humid, cold	Enclosed, dry, warm
Medium	Flowing water (~3x air)	Still air
Cause of death	Blood loss, dehydration	Septicemia, convulsions (higher temp at death)

Henssge Nomogram

A nomogram using body weight and ambient temperature is used to calculate PMI from the rectal temperature.

The Essentials of Forensic Medicine and Toxicology, 36th edition (2026), p. 159-160

II. LIVOR MORTIS (Postmortem Hypostasis / Hypostasis)

After circulation stops, blood settles by gravity into the dependent vessels and capillaries, producing a purplish-red discoloration of the skin in the dependent areas of the body.

Time Course

Phase	Time	Feature
Onset	30 min - 2 hours	Faint pink patches
Becomes obvious	3-4 hours	Well-defined staining
Fully established	6-12 hours	Complete staining
Fixation (non-blanchable)	6-12 hours	Vessel walls become permeable; blood diffuses into tissues

Distribution

Supine position: Neck, back, flanks - sparing bony prominences (shoulder blades, buttocks, heels - contact pallor/blanching)
Prone position: Face, chest, anterior abdomen - Tardieu spots common, more intense
Hanging: Hands, feet, lower legs (glove-and-stocking distribution)
Areas under pressure (belt, waistband, tight clothing) remain pale - called vibices

Color Variations (Forensically Important)

Color	Cause
Bluish-purple	Normal
Cherry-red / bright red	CO poisoning, cyanide, refrigeration
Chocolate brown	Methaemoglobinaemia (nitrites, chlorates)
Pink	CN poisoning

Fig: Cherry-red PM hypostasis in CO poisoning

Medicolegal Significance

Confirms death
Helps estimate time of death (unreliable due to variability)
Indicates posture at time of death
Indicates if the body was moved after death (double lividity / redistribution)
Color may indicate cause of death
Distribution pattern may suggest manner of death

The Essentials of Forensic Medicine and Toxicology, 36th edition (2026), p. 160-162
DiMaio's Forensic Pathology, 3rd Edition, p. 33

III. RIGOR MORTIS (Cadaveric Rigidity)

Stiffening of muscles after death, due to depletion of ATP. Without ATP, actin-myosin cross-bridges cannot be broken, becoming permanently linked - forming actomyosin, causing stiffness.

Three Stages of Muscular Changes

Primary flaccidity (lasts 1-2 hours) - all muscles relax, joints flexible, body flattens
Rigor mortis - progressive stiffening
Secondary flaccidity - caused by putrefactive alkaline liquids dissolving actomyosin

Time Course (at moderate temperature, ~21°C)

Event	Approximate Time
Onset	1-2 hours
Well-marked	6-12 hours
Complete (all muscles)	12-24 hours
Starts to pass off	24-36 hours
Complete resolution	48-72 hours

Important Features

Affects all muscles simultaneously but first evident in smaller muscles (face, jaw, hands)
Nysten's Law: Classically described as progressing downward (jaw → neck → trunk → limbs), but this is disputed; modern view is all muscles stiffen at the same rate - small muscles become apparent first
Can be broken by passive stretching, but will not return once broken
Can be fixed in a new posture if moved before fixation

Factors Affecting Rigor Mortis

Factor	Effect
High temperature	Speeds onset, shorter duration
Cold temperature	Delays onset, prolongs duration
Physical exertion before death	Accelerates onset (depletes ATP)
Emaciation	Weak or no rigor
Drowning	May develop within 2-3 hours
Excited delirium, convulsant poisons	Accelerate onset

Variants of Rigor

1. Heat Stiffening

Caused by coagulation of muscle proteins when body temperature >65°C (burns, lightning)
Produces pugilistic (boxer's) posture - flexion of arms and legs
Cannot be broken by extending limbs (unlike rigor)
Normal rigor does not occur afterward

2. Cold Stiffening

Freezing of body fluids and solidification of subcutaneous fat
At -5°C or below
When joints forcibly flexed, ice breaks in synovial fluid with a sharp sound
Normal rigor occurs after thawing, but passes off quickly

3. Cadaveric Spasm (Instantaneous Rigor)

Rare condition; group of muscles actively working at the moment of death immediately stiffen - no primary relaxation
Usually involves hands (e.g., victim grips weapon, weeds, etc.)
Mechanism: possibly neurogenic, failure of muscular relaxation due to adrenocortical exhaustion impairing ATP resynthesis
Predisposing factors: intense physical/emotional activity, cerebral hemorrhage, strychnine poisoning, drowning, firearm wound to head
Cannot be produced after death - hence great medicolegal significance (proves item was held at moment of death)
The Essentials of Forensic Medicine and Toxicology, 36th edition (2026), p. 162-178
DiMaio's Forensic Pathology, 3rd Edition, p. 34-38

IV. DECOMPOSITION

Decomposition involves two processes: autolysis and putrefaction.

A. Autolysis

Self-digestion of tissues by the body's own enzymes after cell membranes break down.

Lysosomal hydrolases cause autodigestion without bacterial involvement
Earliest in: intestinal lining, adrenal medulla, pancreas (within hours of death)
Brain of newborns/infants undergoes early softening and liquefaction
Increased by heat; stopped by freezing

B. Putrefaction

Decomposition by bacteria (mainly from the gut - Clostridium, Proteus, Bacteroides, etc.), producing gases and liquefaction of soft tissues.

Putrefactive Gases

Hydrogen sulphide (H2S), methane (CH4), ammonia, CO2, phosphine (PH3) - causing foul odor.

External Sequence of Changes

Timeframe (summer)	Changes
12-24 hours	Greenish discoloration of right iliac fossa (overlying cecum - greatest bacterial load); first external sign
24-48 hours	Discoloration spreads over abdomen, foul odor begins
2-3 days	Skin blisters (bullae) form, marbling (arborescent pattern over skin due to haemolysis in vessels), bloating begins
4-7 days	Face bloated, tongue protruding, eyes bulging, gaseous distension of abdomen
2-3 weeks	Epidermis separates, body cavities rupture
Months	Tissues liquefy, skeleton exposed

Marbling: Green-black branching/arborescent discoloration due to hemolysis in superficial veins - a distinctive sign
Postmortem purge: Bloodstained frothy fluid from mouth/nose due to gas pressure (not injury)

Internal Organ Order of Putrefaction

Larynx and trachea
Stomach, intestines, pancreas, spleen
Liver, lungs
Brain
Heart
Kidneys, bladder
Prostate, uterus
Skin, muscle, tendon
Bones

Conditions Affecting Rate of Putrefaction

Factor	Accelerates	Retards
Temperature	21-38°C optimal	<0°C, >48°C arrests it
Moisture	Moist environment	Dry environment
Air	Free air access	Closed/anaerobic environment
Clothing	Initially hastens	Later retards
Burial	Shallow, sandy soil	Deep burial (>2 m)

Casper's Dictum: A body decomposes in air twice as rapidly as in water, and eight times as rapidly as in earth.

The Essentials of Forensic Medicine and Toxicology, 36th edition (2026), p. 171-175

V. LATE CHANGES / SPECIAL FORMS OF DECOMPOSITION

1. Adipocere (Saponification)

Conversion of body fat into a waxy, soap-like substance (saponification) when the body is in a warm, moist, anaerobic environment.

Mechanism: Intrinsic lipases + bacterial enzymes (mainly Cl. perfringens lecithinase) hydrogenate and hydrolyze body fat into higher fatty acids (palmitic, stearic, hydroxystearic acids)
Onset: As early as 3-5 weeks in warm conditions; months in cold
Conditions favoring: Warm, moist, anaerobic environment; obesity; immersion in water; burial in wet soil
More common in: Females, obese individuals, well-nourished neonates
Odor: Distinctive offensive/sweetish smell; ammoniacal in early stages
Color: White/grey-white, later yellowish-brown; greasy texture
Medicolegal value: Preserves body contours and injury evidence for long periods (years); allows identification; may preserve poisons

Fig: Adipocere

2. Mummification

Desiccation and drying of the body, preventing putrefaction.

Conditions favoring: Hot, dry, well-ventilated environment; desert conditions; dry sandy soil
Time: Several months (complete mummification)
Features: Skin becomes brown, leathery, hard, and brittle; body weight greatly reduced; no putrefactive smell
Medicolegal value: Preserves features and injuries for identification; may survive for centuries

3. Maceration

Softening and disintegration of tissues in a sterile fluid environment without putrefaction.

Occurs mainly in a dead fetus in utero (amniotic fluid is sterile)
Features: Skin becomes red/brown, wrinkled, peels off; bones become soft; no offensive odor
Types by timing after fetal death:
- Early (<12 hours): Skin peeling, bullae formation
- Late (>48 hours): Brownish discoloration, overlapping skull bones, wrinkled skin

4. Skeletonization

Complete removal of soft tissues leaving only the skeleton.

In tropical, humid conditions with heavy insect/scavenger activity: days to weeks
In buried bodies: months to years
In water: Attacked by fish, crustaceans

Summary: Medicolegal Importance of PM Changes

Change	Use
Algor mortis	Estimate PMI (Henssge nomogram)
Livor mortis	Position at death, body movement, cause of death (color)
Rigor mortis	PMI estimation; cadaveric spasm = item held at moment of death
Putrefaction	PMI (broad estimate), conditions of death
Adipocere/mummification	Preserves evidence; long-term PMI estimate

Sources: The Essentials of Forensic Medicine and Toxicology, 36th edition (2026); DiMaio's Forensic Pathology, 3rd Edition; Parikh's Textbook of Medical Jurisprudence, Forensic Medicine and Toxicology.

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