What is forensic dermatology?
- This can provide important insight in the medicolegal autopsy, particularly in cases where the death is violent, unexplained, suspicious, or unexpected.
- The dermatologist may also encounter classic presentations of abuse, neglect, or torture, in clinical practice.
The study of ridgeology or digital friction ridges (fingerprints) may also be important in the identification of bodies (or criminals).
What are the normal changes to skin after death?
A study of the skin is particularly important to determine the time of death, which can be estimated within the first 48 hours of death.
Algor mortis, which refers to cooling of the body, is one of the earliest changes observed and is confirmed by checking the skin temperature of the body. It is used to accurately estimate time of death.
Following death, there are some dermatological findings that are normal and distinct from traumatic injuries:
- Livor mortis, also called post-mortem hypostasis
- Cutis anserine (goose bumps)
- Decomposition of the body
Rigor mortis is stiffening of joints and muscles of a body a few hours after death, and lasts from one to four days.
Livor mortis refers to the staining of skin where blood has pooled in the vessels. Because blood remains as a fluid following death, the location of livor mortis can be a useful clue indicating if the body has been moved after death.
The colour of livor mortis can also be useful. Carbon monoxide poisoning may be associated with pink livor mortis, while brown and dark bluish-gray livor mortis may indicate methaemaglobinaemia due to carbon monoxide poisoning.
Six hours after death is the best moment to observe livor mortis1, and it is always absent in areas of mechanical compression on the body, such as at contact points in clothing.
Cutis anserina is caused by rigor of the pili erector muscles (attached to the body’s hair follicles), and is an early sign of rigor mortis.
Decomposition of the body
Decomposition of the body is a natural process that occurs due to postmortem increased bacterial activity and release of cellular enzymes. From 24 to 36 hours postmortem, a green discolouration of the abdominal skin over the right caecum becomes evident due to accelerated decomposition of the intestines. The colour is the product of the metabolism of haemoglobin by bacteria from the intestine.
‘Marbling’ over the trunk and limbs is another feature of postmortem skin decomposition, caused by the spread of bacteria through the venous system.
From 60 to 72 hours postmortem, the body exhibits generalised swelling and bloating from increased gas production by bacteria. Blister formation, with skin and hair breakdown, occurs at 3 to 5 days. From 3 to 4 weeks, hair and nails detach from the body.
Normal postmortem tissue changes noted on histopathology include focal dermal-epidermal separation (a split between the two layers of the skin), eccrine (sweat) duct necrosis, and dermal degeneration within 1 week of death.
What are patterns of injury seen in forensic dermatology?
The appearance of the wound can provide information on the shape of the penetrating weapon and the force exerted on the body. Cutaneous injuries are classified into three main categories:
- Blunt – including abrasions, contusions and lacerations
- Sharp – including incision, stabs, and chop injuries
- Non-kinetic – chemical, thermal, or electrical injuries
Specific dermatological patterns of injury include:
- Cigarette burns: circular lesions with a central depression and rolled edges
- Gunshot wounds
- Bite marks: circular or semi-circular, with bruising around each tooth mark
- Asphyxia (suffocation): facial swelling, cyanosis (blue discolouration), and conjunctival bleeding
Analysis of hair and nail samples often also provides information concerning anything that the victim may have ingested or been exposed to.
- Hair can be examined for exposure to dye or bleach.
- Hair and nails can be submitted for toxicology and drug screening.
- The DNA of the perpetrator may be isolated from under the fingernails of the victim.
What patterns of injury may a dermatologist encounter?
A dermatologists may note skin findings suspicious of abuse during a consultation. These must be carefully documented, measured, and photographed. The distribution and shape (morphology) of the markings are particularly important. It is important to distinguish dermatological disorders from true physical abuse.
The classic sign of child abuse is loop marks – which result from injury inflicted by ropes, cords, or belts.
Sexual abuse can present with characteristic markings found on the victim or perpetrator, such as bruising, bite marks, fingerprint marks, abrasions from ligatures, and petechiae (tiny bruises) from asphyxia (suffocation).
A normal examination does not rule out the possibility of abuse. Victims may present with nonspecific symptoms or sexually transmitted infections. Not all genital injuries are abuse-related. Skin conditions that may mimic sexual abuse include lichen sclerosus, allergic contact dermatitis, fixed drug eruptions, and infection. Excessive bruising may be due to a bleeding disorder such as haemophilia.