Acquired symmetrical dermal melanocytosis (naevus of Hori) developing after aggravated atopic dermatitis

Acquired symmetrical dermal melanocytosis (ASDM) is a pigmentary disorder characterized by blue-brown macules most frequently seen on the face of young and middle-aged Asian women. ASDM developing after other skin diseases has not been previously reported.

To characterize the clinical and histopathological features of ASDM associated with atopic dermatitis (AD) and to elucidate the differences between AD-associated ASDM and idiopathic ASDM.

Sixteen patients with ASDM associated with AD were examined clinically and histopathologically and were compared with 69 patients with idiopathic ASDM.

The AD patients associated with ASDM consisted of four men and 12 women with a mean age of 32.8 +/- 13.1 years. Most patients remembered that the pigmented macules appeared in places where refractory eczema had existed for a long time. The marked preponderance in females and the appearance in the early reproductive period were common features of AD-associated ASDM and idiopathic ASDM. AD-associated ASDM was most commonly observed on the forehead (68.8%) and on the backs of the hands (50.0%), whereas 89.9% of idiopathic ASDM was seen on the cheeks. There was no significant difference in the number of dermal melanocytes between AD-associated ASDM and idiopathic ASDM. Electron microscopic studies demonstrated many mature melanocytes and smaller numbers of immature melanocytes in the dermis. Some melanocytes were seen adjacent to mast cells.

AD-associated ASDM does not appear to be rare in Japan. ASDM may be triggered in AD patients by sunlight exposure, some alterations in sex hormones and/or persistent cutaneous inflammation. Histamine and stem cell factor produced by mast cells may play crucial roles in the pathogenesis of AD-associated ASDM.