Syringomatous changes of eccrine sweat ducts associated with prurigo nodularis.

Alteration of the eccrine sweat ducts has been observed in association with an expanding list of conditions. To our knowledge, this phenomenon has not been described in association with prurigo nodularis. We report on a 68-year-old man with a fibrotic nodule on his chin that had been present for 8 months. Microscopic examination showed marked hyperkeratosis overlying the epithelium. There was also hypergranulosis, marked acanthosis, and irregular elongation of the rete ridges. These findings were consistent with prurigo nodularis. In addition, within the reticular dermis, there was marked fibrosis and a proliferation of eccrine sweat ducts. The ducts were enlarged and varied from cystic to rarely solid structures. Rare ducts formed a tadpole-shaped tail, reminiscent of syringoma. The duct lining demonstrated a multilayered epithelium that was three to eight cells thick, yielding a solid component to some of the cysts. Although some of these features were similar to those of a syringoma, the typical small gland proliferation and bilayered lining was not evident. This case (a) demonstrates the association of syringomatous changes of eccrine sweat ducts with yet another condition, prurigo nodularis, and (b) emphasizes the importance of differentiating this benign reactive process from the malignant neoplasms microcystic adnexal carcinoma and squamous cell carcinoma.