Perifollicular CD163+/CD68+ foam histiocyte infiltration in asymptomatic adolescent axillary fox-fordyce disease: a case report of cutaneous apocrine gland-associated local inflammatory phenotype

Fox-Fordyce disease (apocrine miliaria) is a classic apocrine gland-related inflammatory skin disorder, and most previously documented clinical cases present with severe pruritus. We report a rare case of bilateral axillary Fox-Fordyce disease in a 14-year-old adolescent girl, distinguished by prominent perifollicular foam histiocyte aggregation with co-expression of pan-macrophage marker CD68 and scavenger receptor CD163. A full panel of eight immunohistochemical markers verified negative expression of multiple lineage-specific biomarkers in these foam cells. The patient presented with six months of painless, non-pruritic symmetric follicular papules confined to bilateral axillae, without burning sensation, exudation, or lesions on other apocrine-rich body sites. Specimens obtained via conventional skin biopsy were subjected to histopathological testing, which revealed follicular keratotic plugs, follicular epithelial hyperplasia, mild epidermal spongiosis, dilated hyperactive apocrine glands, and mixed perifollicular inflammatory infiltrates consisting of lymphocytes, plasma cells and abundant foam-like histiocytes. Immunohistochemical testing confirmed the foam cells were CD163(+) and CD68(+), while S100, SMA, EMA, Langerin, ALK1 and CD34 were all negative, consistent with the pathognomonic perifollicular xanthomatosis characteristic of Fox-Fordyce disease. This case objectively describes the unique local inflammatory cell phenotype dominated by CD163/CD68 double-positive foam histiocytes within non-pruritic Fox-Fordyce lesions. We systematically discuss the correlation between apocrine gland secretory activity, follicular stromal inflammatory infiltration and foam histiocyte formation, analyze the differential diagnostic value of this CD163/CD68 immunophenotype across apocrine inflammatory dermatoses, and explore the research value of CD163+/CD68+ foam histiocytes as tissue-resident antigen-presenting cells in sterile cutaneous inflammation.