Clear-Cell Hyperplasia of Eccrine Sweat Ducts

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To the Editor:
Eccrine sweat glands in humans consist of a secretory coil (glomerulus) and an excretory duct. The former is composed histologically of 1–2 rows of secretory (clear and dark) cells, lined peripherally by a discontinuous layer of myoepithelial cells. The excretory duct traverses the dermis vertically and enters the epidermis, where it forms an individual, coiled structure (acrosyringium); it is made of a double row of cuboidal, basophilic cells surrounding the lumen of the sweat duct.1 In some people (accounting for about 0.5% of the population at large according to a recent study),2 the secretory coil contains only clear cells, resulting in a characteristic vacuolated/foamy appearance, which has no clear pathological implication. The presence of clear cells in the excretory ducts is an exceptional finding. It has been reported in the so-called “papular eccrine duct hyperplasia (PEDH),” a very rare condition of which 4 cases have been so far reported.3–6 This condition, which is different from clear-cell syringomas,7 was originally described as “eruptive clear cell hamartomas of sweat duct”3 and is characterized microscopically by a hyperplasia of the dermal ducts and the acrosyringium, which contain clear cells. A case similar to PEDH is reported herein, showing prominent clear-cell ductal hyperplasia found incidentally in a skin biopsy. The significance of this rare peculiar pathological finding is discussed.
A 67-year-old white man of Italian origin had a medical history of arthropathic psoriasis since the age of 20 years, for which he had received several therapies, including systemic (Psoralen plus Ultraviolet ray A, retinoids) and local ones (steroids, vitamin D analogs). He was also followed for alcoholic hepatic cirrhosis and for intestinal tubular adenomas with low-grade dysplasia. Increased fasting blood glucose levels were detected on several occasions during his regular follow-up for hepatic cirrhosis. During one of his visits, he presented with an erythematous, circinated, slightly atrophic scapular skin lesion that had reportedly been present for 4 years. A skin biopsy was taken from the lesions and submitted with the clinical suspicion of seborrheic dermatitis or lupus erythematosus. Microscopic examination of routinely stained 5-μm-thick sections cut from formalin-fixed, paraffin-embedded tissue blocks showed dermal capillaries somewhat dilated and surrounded by scarce lymphoid cells. The deep dermis contained eccrine sweat glands whose secretory coils looked normal. Remarkably, the proximal dermal excretory duct contained a peripheral row of cuboidal clear cells and an inner row of more basophilic cells surrounding the lumen (Fig. 1A). The upper dermal excretory duct was hyperplastic, consisting of 2–4 rows of large, polygonal cells with a clear cytoplasm, surrounding a narrow lumen. The clear cells had small basophilic monomorphous nuclei devoid of atypia and mitoses. The corresponding acrosyringium was also made of clear cells, the inner row of which contained small keratohyalin granules (Fig. 1B). Periodic Acid-Schiff staining highlighted the cuticle lining the excretory lumen and very weakly, if at all, some clear cells (Fig. 1C). Alcian blue staining showed normal mucin deposits around the secretory coils. Immunohistochemically, the clear cells of the hyperplastic eccrine ducts expressed membranous reactivity for the epithelial membrane antigen (Fig. 2A), the CD138 antigen (syndecan-1), and more weakly of EGF-R. Their nuclei expressed p63 (Fig. 2B). Cells of the inner row of the clear-cell ducts expressed K19 (Fig. 2C). HLA-DR antigens (revealed with the LN3 monoclonal antibody) were expressed by the inner row of acrosyringeal cells and more weakly by cells of the inner row of the dermal duct. Weak luminal expression of GCDFP-15 was seen, as well as weak expression of keratin 5/6 within basal cells of the hyperplastic ducts.
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