Reticulohistiocytosis: different dermatoscopic faces and a good response to methotrexate treatment

The reticulohistiocytoses are a rare group of non-Langerhans cell histiocytic disorders. Recently, dermatoscopic features have been reported for some of the xanthomatous disorders. We report a case of diffuse cutaneous reticulohistiocytosis with 29 reticulohistiocytomas. On dermatoscopy of these lesions, we saw three typical features: a homogeneous pattern with various shades of yellow (defined previously as a 'setting-sun' pattern), brown reticular structures, and central white scar-like patches and streaks. The setting-sun pattern was most commonly seen in combination with brown reticular structures. In four lesions, brown reticular structures surrounded a central white scar-like patch resembling that of a dermatofibroma. However, the presence of the setting-sun pattern in the background gave a different hue to that of the peripheral network seen in a dermatofibroma. A marked clinical improvement was associated with 6 months of systemic methotrexate treatment. Dermatoscopy may aid in the diagnosis of xanthomatous diseases. For this patient, methotrexate was beneficial.