[Epidermal hamartoma and blaschkitis in an adult].

INTRODUCTION

Many inherited skin diseases and nevus malformations are distributed according to the Blaschko's lines. Some inflammatory skin diseases are also distributed according to these lines.

OBSERVATION

In 1989 a 49-year-old woman presented with an epidermal nevus affecting the left hand and leg from the infancy. In 1994, inflammatory, linear papules occurred on the left leg, obscuring and continuing the previous lesions, on the left thigh and on the left clavicular region. On light microscopy, spongiosis of the epidermis and an infiltrate of lymphocytes and histiocytes in the superficial dermis were shown. Subintrant crops of new inflammatory lesions occurred for a period of two years, whereas the nevus lesions of the left hand persisted unchanged. These findings led to the final diagnosis of blaschkitis associated to epidermal nevus on the same Blaschko's lines.

DISCUSSION

The distribution of a skin disease according to the Blaschko's lines underlines the presence in the affected skin of a mutant clone, with a different genetic material as compared with the normal skin. An early mutation giving raise to a mutant clone and affecting the left hemibody could be hypothesized in our case. The mutation probably involved a pleiotropic gene. The latter initially was responsible for thickening of the skin. Moreover, the mutation was also responsible for a particular proneness towards an exogenous factors, able to induce a persistent inflammatory skin eruption following the same lines.