Types of EB
EB can be devided into three main types:
- EB Simplex
- Junctional EB
- Dystrophic EB
This division is made on the basis of the located disruption (mechanical defect) in the basement membrane of the skin. The location of the defect determines the symptoms of each type of EB.
Every main type can again be divided into several variations and currently, 27 clinical sub-types are known.
EB Simplex is characterised by lack of adhesion of the skin right above the basement membrane (the basal layer). Approximately 70% of people with EB suffer from EB simplex. Most forms of EB simplex are inherited as dominant traits i.e. the parents visibly have the condition. Because of this, the family history has already shown that there is a possibility of having a child with EB simplex. However, sometimes a patient is confronted with the disorder for the first time, a so-called new mutation. THe most common form of EB simplex has blistering confined to hands and feet. These patients usually do not seek medical assistance because the disorder is mild and because it is well known in the family due to the dominant inheritance.
In another form of EB simplex blistering can occur all over the body. Blistering may appear during the neonatal period but it can also manifest itself in later childhood (or even in adult life). Rubbing tends to be the main cause for blistering and especially rubbing of the feet by footwear. Rubbing is worse in warm weather.
Dystrophic EB is characterised by a lack of adhesion of the skin under the basement membrane. Approximately 25% of all EB sufferers have dystrophic EB. The dystrophic type may be inherited as a dominant or a recessive trait. The recessive inheritable types may lead to major handicaps and a relatively short and painful life. However, there are many exceptions to this rule. Dystrophic EB derives its name from the tendency of the blisters to heal with scarring. This process can lead to contraction of the joints, fusion of the fingers and toes, contraction of the mouth membranes and narrowing of the oesophagus.
There is a wide variation in the severity of dystrophic EB. In general, dystrophic EB is not life-threatening in childhood. At its least severe (this is often the dominant inheritable type of dystrophic EB) the patient can lead an almost normal life. However, the severity of the disorder does increase at a later age due to scarring, fusion of fingers and wastage of skin tissue. In the recessive type of dystrophic EB there is a high chance of developing a squamous cell carcinoma (aggressive skin cancer) before the age of 35. Eventually 40% of the patients with this type of EB die from the effects of squamous cell carcinoma.
Junctional EB is characterised by lack of adhesion of the skin through the basement membrane. Of all EB sufferers approximately 5% have junctional EB. Junctional EB is inherited recessively i.e. the parents are carriers, often unknowingly, and do not show physical signs of the condition. The birth of a child with junctional EB is therefore, totally unexpected.
The outlook of junctional EB is usually rather bleak; half of the children die within the first two years as the result of malnutrition and anaemia which are caused by serious blistering in the pharynx and the oesophagus. Characteristic clinical features are damage to and marking of the skin tissue on the face. These cutaneous defects only develop after a couple of months. There are only a few patients with this severe type that survive the second or third year of life. The other half of the children have a milder form of junctional EB which does not impose life restrictions.