There are two distinct subtypes of IgA pemphigus: the subcorneal pustular dermatosis (SPD) type (or IgA pemphigus foliaceus) and the intraepidermal neutrophilic (IEN) type (or IgA pemphigus vulgaris). The SPD type is slightly more common. Both occur in middle-aged or elderly persons with a slight female predominance.
In both types, patients present with flaccid pustules or erosions on red or normal skin that form circinate patterns with crusting. Sites of predilection are the axillae and groin but other areas may be involved. Mucous membrane involvement is rare and lesions are typically associated with significant pruritus. In addition, patients may have an associated IgA monoclonal gammopathy.
Light microscopic exam of the SPD type reveals subcorneal pustules or bullae while exam of the IEN type reveals suprabasilar pustules. Both demonstrate sparse, superficial acantholysis and a significant neutrophilic infiltrate. The target antigen of the SPD type is desmocollin 1 whereas the target antigens of the IEN type are desmogleins 1 and 3. In both, circulating antibodies to these antigens may induce ancantholysis. For the SPD type, direct immunofluorescence of perilesional skin demonstrates intercellular IgA limited to the upper epidermal cell surfaces. In contrast, direct immunoflourescence of perilesional skin in patients with the IEN type reveals intercellular IgA restricted to the lower epidermis or throughout the entire epidermis. In both types, indirect immunofluorescence is positive only about 50% of the time.
Both types of IgA pemphigus respond well to appropriate therapy. Both tend to follow a chronic and benign course.