The ultrastructural histopathology of eosinophilic pustular folliculitis.

The follicular skin lesions of a patient with eosinophilic pustular folliculitis were investigated by electron microscopy. Pustules in the outer root sheath contained acantholytic keratinocytes with numerous microvilli and features of desmosomal cleavage. The infiltrating eosinophils and neutrophils exhibited autolytic or degenerative changes rather than degranulation. The aggregated tubulo-vesicular structures were associated with the debris of autolytic eosinophils. Multiple, tiny, bubble-like structures enclosed within a membrane were frequently seen in the intercellular space. The intercellular space of the outer root sheath was widened with decreased desmosomal adhesion between the keratinocytes, but no intracellular edema was detectable. The infiltrating lymphocytes, predominantly T-cells with convoluted nuclei, extended cytoplasmic processes to adjacent keratinocytes. Apposition of T-lymphocytes and Langerhans cells was noted. Some keratinocytes in the outer root sheath contained large, sebaceous lipid droplets. No obvious virus particles or other pathogenic agents were detected. It is possible that T-lymphocytes and other immunosurveillance cells are involved in the pathomechanism of eosinophilic pustular folliculitis.