Author: Dr Stephanie Ball, Dermatology Registrar, Royal Infirmary of Edinburgh, Scotland. Chief Editor: Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand, October 2015.
Epidermolysis bullosa pruriginosa (EB pruriginosa) is a rare and clinically heterogeneous subtype of dystrophic epidermolysis bullosa (dystrophic EB), resulting from a mutation within the type VII collagen gene.
EB pruriginosa is characterised by intensely itchy (pruritic) hypertrophic plaques in a linear configuration, usually found on the lower extremities of an affected individual. First described in 1994, there have been fewer than 100 cases documented in the literature, and as such, little is known about the condition or its treatment.
EB pruriginosa can either present shortly after birth, or in early adulthood.
As with other forms of dystrophic EB, the clinical findings EB pruriginosa are attributed to mutations in the COL7A1 gene on chromosome 3p21.3, which encodes type VII collagen. The case reports of epidermolysis bullosa pruriginosa reveal many different alterations to this gene, including missense, nonsense, frame shift and splice-site mutations.
Type VII collagen is a major skin structural component of the anchoring fibrils at the dermo-epidermal junction (DEJ). Mutations in the coding gene hamper the function of the anchoring fibrils and lead to a split in the DEJ below the level of the lamina densa. Clinically, this manifests as trauma-induced blisters, which on healing leave a scar.
Inheritance is variable; most cases have been found to be sporadic. Autosomal dominant and autosomal recessive patterns have also been reported.
The characteristic pruritic component of the condition is poorly understood. A raised serum IgE level has been found in 7 of 9 examined patients with epidermolysis bullosa pruriginosa, and in some cases was found to be over 3 times the upper limit of normal. However, a personal or family history of atopy was a confounding factor in three of these patients, and so the results are far from conclusive.
It has been suggested that the hypertrophic, lichenified, nodular prurigo-like plaques seen in the disease are secondary to chronic scratching.
The classical appearances of EB pruriginosa are intensely pruritic, excoriated, lichenified violaceous papules, nodules and plaques. These are usually linear in configuration, and most commonly affect pre-tibial skin, though can also be seen on the forearms and trunk. The face, neck and flexures are spared. Nail dystrophy is very commonly seen, and helpful in distinguishing from other conditions. The prurigo-like lesions are due to scarring, and milia are seen within them.
Differential diagnoses include:
A presumed diagnosis of EB pruriginosa can be achieved based on the clinical findings in conjunction with a positive mechanobullous history and clear evidence of inheritance within the family. When diagnosis is uncertain, skin biopsies for light microscopy and for electron microscopy are helpful.
The histological features of EB pruriginosa comprise hyperkeratosis, acanthosis and disruption of the DEJ, with a prominent dermal and perivascular lymphohistiocytic infiltrate. A subepidermal blister may be seen, though rarely evident clinically, as can milia formation.
Electron microscopy can be valuable to confirm the level of the split, and should show diminished or absent anchoring fibrils in the sub-lamina densa beneath the basal layer of the epidermis. Direct immunofluorescence of perilesional skin is negative, but may be a helpful investigation to exclude other bullous conditions.
Genetic sequencing will demonstrate mutations in COL7A1.
Success has been varied, and no sustained effect has been reported.
Little is known about the long-term outcome for patients with EB pruriginosa. It is chronic and often refractory to treatment. Complications have included lymphoedema of the lower limbs, and a single case has been reported of a well differentiated squamous cell carcinoma in affected skin.
Some patients have responded very well to the treatments listed above, but no long term data exists with regards to the sustainability of medication-induced remission.
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