General description
Epidermolysis Bullosa Simplex manifests itself at birth or during early childhood. It is the most common and least severe form of EB (75% of cases). It is inherited from one parent presenting with the mutated gene.
All types of EB are characterised by the separation of the skin at the level of the keratinocytes (cells that make up a large part of the skin and that synthesise keratin, which makes the skin impermeable) in the basal layer of the epidermis, without altering the membrane itself.
The symptoms of this illness vary considerably amongst those affected. In benign cases, the blisters generally only affect the hands and feet and usually heal without scarring. It is possible to lead a normal life if affected by the disease at this level. Individuals with a more severe form display numerous blisters distributed all over the body, which can potentially lead to infection, dehydration and other medical problems. Severe cases may be life-threatening.
There are many variants of EBS; the three most common are inherited via a dominant autosome. Rarer forms include a recessive variant. All these types are characterised by secondary blisters caused by friction or minor trauma.
The exact prevalence of Epidermolysis Bullosa Simplex is unknown, but this condition is estimated to affect 1 in 30,000 to 50,000 people. The Weber-Cockayne type is the most common form of the condition.
Epidermolysis bullosa simplex may be divided into the following types
- Localized Epidermolysis Bullosa Simplex : Weber-Cockayne
- Generalized Epidermolysis Bullosa Simplex : Koebner
- Epidermolysis Bullosa Simplex with mottled pigmentation
- Epidermolysis Bullosa herpetiformis: Dowling-Meara
The most benign form of Epidermolysis Bullosa Simplex is known as Weber-Cockayne. It generally manifests itself as soon as the child begins to walk, sometimes a little later. The blisters are located on the feet and hands (palmoplantar). The skin displaying the blisters may become thicker and harder during the child’s life (hyperkeratosis) as the skin successively separates and scars.
In the Koebner form of the disease, the blisters are apparent from birth or at a very young age and are more widely distributed. Blistering may occur at friction points during labour. The affected areas will initially be limited to the hands, feet, elbows, knees and rear in the infant, and will only affect the feet and knees as the child begins to walk. The blisters are light in colour, vary in size, are formed in response to friction and trauma and appear more frequently in warm conditions. They heal without scarring, except for temporary pigmentation in some cases. The nails are not permanently affected and the teeth are normal. The illness becomes markedly less severe as the child approaches puberty, but the skin remains fragile throughout life.
Koebner EBS results from minimal modifications to the cytoskeleton of epidermal cells with reduction or condensation of the tonofilaments affecting the architectural cohesion of the epidermis.
The Simplex with spotted pigmentation is characterised by deeper abrasions on the torso, arms and legs, which wrinkle as the child becomes an adult. This form is associated with blisters which begin in early childhood, hyperkeratosis of the hands and soles of the feet and abnormal nail growth.
The Downling-Maera type is the most severe form of Epidermolysis Bullosa Simplex. The abrasions may appear anywhere on the body, including the oral mucous tissue, and they spread. The blisters are present from birth, but they decrease with age. They do not necessarily appear as a result of trauma. Mucosal and unguis lesions are also possible. Those affected may also experience abnormal nail growth and hyperkeratosis on the hands and soles of the feet.
This form is characterised from a histological perspective by suprabasal separation of the skin, within the keratinocytes of the basal layer of the epidermis. Under an electronic microscope, it is possible to observe intracytoplasmic aggregates of tonofilaments in the cells of the base layer, suggesting that anomalies in the cytoskeleton are pathogenic in EBS. In immunohistochemical terms, these concentrations are recognised by the antibodies working against the base keratins in the epidermis.