This is a great example of a rare case of rheumatoid neutrophilic dermatosis. This patient had severe rheumatoid arthritis and developed plaques and bulla over the forearms. Rheumatoid neutrophilic dermatosis is a rare manifestation of severe joint disease, as in this case. Histologically, this is one of the neutrophilic dermatoses along with Sweet syndrome, cellulitis, pyoderma gangrenosum and others. The bulla are often secondary, and not always seen. Distinction between these entities is virtually impossible without clinical history.
There is separation of the epidermis from the dermis in a subepidermal plane. The papillary dermis is filled with neutrophils. The infiltrate extends to the mid demis.