The pathogenesis of Prurigo nodularis--'Super-Itch' in exploration.

Prurigo nodularis (PN) is characterized by multiple hyperkeratotic nodules, papules and the presence of intensive pruritus. This leads to an impaired quality of life and high burden due not only to the severe itch but also the chronic, skin lesions and lack of treatment options. The pathogenesis of PN is not completely clarified. Previous studies have demonstrated just how important the interaction between cutaneous nerve fibres and immune cells is. Besides a reduced intraepidermal nerve fibre density, there are increased dermal levels of neuropeptides such as substance P, calcitonin gene-related peptide and nerve growth factor, as well as a predominant presence of eosinophils and mast cells. An interaction of these factors results in a complex relationship which will be discussed in this article.