Diagnosis of Immune-mediated Skin Disease

Immune-mediated skin diseases come in many varieties with varied clinical signs. There are some clinical or historical clues that make these diseases more likely and should lead to a more aggressive diagnostic work-up early on in the disease. An immune-mediated disease should be considered when
• historically the disease had an acute onset and the patient rapidly deteriorates.
• mucous membranes or mucocutaneous junctions are affected
• skin lesions are only part of the disease and other organ systems seem to be involved (joints, kidney, etc.).
• the planum nasale is affected.

Cytology may be useful in the diagnosis of diseases of the pemphigus complex. An impression smear is most commonly used. The slide is gently pressed against an eroded, exsudative or ulcerated area (if non it present, one can carefully peel off a crust and sample the eroded surface underneath) and stained with DiffQuick. In many patients with pemphigus, acantholytic keratinocytes will be identified. These cells stain blue to purple, are round and have a central nucleus. They are not diagnostic for pemphigus (as occasionally they can be found in pyodermas as well), but indicate a need for a biopsy and a probability of pemphigus. If an immune-mediated disease is on the list of differential diagnoses, a biopsy is always indicated. [...]