In paraneoplastic pemphigus, there is usually an overt interface or lichenoidinfiltrate associated with necrotic keratinocytes at all levels of the epidermis (figures 1-3) to resemble erythema multiforme. In addition, foci of suprabasal acantholysis are seen. Sometimes the acantholysis can be very difficult to find making diagnosis difficult.
Direct immunofluorescence usually shows intercellular and basement membrane deposition of IgG and C3.
Differential diagnosis of paraneoplastic pemphigus
The features histologically resemble lichenoid eruptions (such as erythema multiforme, lichen planus, drug eruptions), and other immunobullous diseases (pemphigus vulgaris). Correlation with the clinical findings and immunofluorescence is invaluable in arriving at the correct diagnosis.
Weedon's Skin Pathology (Third edition, 2010). David Weedon