Researchers found compelling evidence for the use of CD123, an interleukin-3 receptor, to highlight plasmacytoid dendritic cells (PDCs) when attempting to distinguish acute generalized exanthematous pustulosis (AGEP) and pustular psoriasis (PS). They discovered that the presence of PDCs and expression of MxA protein in dermal inflammatory infiltrate, as well as absence of eosinophils and presence of tortuous dilated capillaries, favored a diagnosis of PS. Therefore, expression of MxA in the dermal infiltrate corresponds with a Th1 pathway in PS, and may indicate a Th1 component in the early initial phase of AGEP. 43 cases of AGEP and PS were compiled from 2 academic institutions. All cases were examined for CD123+ PDCs, eosinophils, acanthosis, papillomatosis, suprapapillary plate thinning, tortuous dilated capillaries, single necrotic keratinocytes, papillary dermal edema, vasculitis, eosinophil exocytosis, intraepidermal pustules, and subcorneal pustules. A subset of cases (n=26) was stained with MxA. They found:
- Perivascular and intraepidermal PDCs, dilated tortuous vessels, and MxA expression in the dermal inflammatory infiltrate, were significantly in favor of a diagnosis of PS.
- The absence of PDCs and presence of eosinophils favored a diagnosis of AGEP.
Vyas NS, Charifa A, Desman GT, McNiff JM. Distinguishing pustular psoriasis and acute generalized exanthematous pustulosis (AGEP) on the basis of plasmacytoid dendritic cells (PDCs) and MxA protein. [Published online ahead of print January 22, 2019]. J Cutan Pathol. doi:10.1111/cup.13430.