Paraneoplastic Erythroderma: A Rare, but Important Cause of Mixed Pattern Dermatitis.

In dermatopathology, mixed inflammatory patterns, such as mixed spongiotic and interface dermatitis (SID) are not well-characterized and can present a diagnostic challenge. This pattern can be seen in drug eruptions, viral exanthems, and syphilis infection. We present two cases of paraneoplastic erythroderma characterized by a mixed pattern SID. The patients underwent an extensive workup and were found to have positive antinuclear antibodies (ANA) in the absence of symptoms diagnostic of connective tissue disease. Eventually, the patients were both diagnosed with malignancies (systemic marginal zone lymphoma and breast cancer). It is important for dermatopathologists to consider paraneoplastic dermatitis in the differential diagnosis of mixed pattern SID, particularly in the clinical setting of erythroderma, as these findings can be the presenting sign of underlying malignancy. Additionally, if antinuclear antibodies are detected in the absence of classic clinical signs of connective tissue disease, a thorough workup should be conducted to exclude malignancy.