Dilation of apocrine glands. A forgotten but helpful histopathological clue to the diagnosis of axillary Fox-Fordyce disease.

Fox-Fordyce disease is a condition with protean histopathological alterations whose pathogenesis remains a mystery. Although recent studies have addressed histological changes specific of this disease, including perifollicular xanthomatosis, no attention has been given to apocrine acini dilation as an adjunct histopathological finding to the diagnosis. Moreover, although previous efforts were done to demonstrate that perifollicular foamy histiocytes harbor apocrine secretion content, this concept has not been proved to date. In this study, we report 2 cases harboring prominent dilation of apocrine coils with mucinous content. Such mucinous content showed mucin profile identical to the dermal mucin deposits in both cases. Of note, perifollicular foamy histiocytes demonstrated cytoplasmic mucin, supporting the suggestion that these cells phagocytose apocrine secretion. Although not specific, apocrine coil dilation is another histopathological feature of Fox-Fordyce disease and it may be used as a low-power magnification clue for the correct diagnosis. We also propose that the so-called perifollicular xanthomatosis may be composed of muciphages or mixed cell (muciphages/xanthomatous) population, an issue that should be further investigated in future studies.