Paraneoplastic pemphigus with negative direct immunofluorescence in epidermis or mucosa but positive findings in adnexal structures

Introduction: Paraneoplastic pemphigus (PNP) is considered an autoimmune, multiorgan disease caused by antiplakin antibodies. We present three PNP patients who had negative epithelial direct immunofluorescence (DIF) findings in one or more biopsies. Patients: An early lip biopsy of uninvolved oral epithelia in patient 1 was negative. A later biopsy from foreskin showed intense intercellular immunoglobulin G (IgG) deposits in the epithelia. In the early phase of the disease in patient 2, the intercellular fluorescence was negative in the epidermis, while intercellular IgG and C3 were observed in the sweat ducts. A later biopsy showed weak intercellular epidermal IgG and C3 fluorescence. Patient 3 showed intercellular IgG and/or C3 in follicular, sebaceous and sweat duct structures in several biopsies. No intercellular IgG or C3 was observed in the epithelia. Discussion: The presence of immunoreactants in adnexal structures suggests that desmoplakins can be more strongly expressed in adnexa than in the epidermis, facilitating visualization of antibody deposits. Conclusions: Negative DIF findings in epithelia do not rule out the diagnosis of PNP, and the presence of IgG and/or C3 at the intercellular level of adnexal structures can help establish this diagnosis.