Ten patients with pustulosis palmaris et plantaris were investigated with regard to the morphological evolution of their condition. The primary eruption was a spongiotic vesicle in the lower Malpighian rete. As long as the entire roof of the cavity was formed by the Malpighian stratum, the contents of the cavity still consisted of mononuclear cells. The pustulation of a vesicle began when the direct contact between the blister fluid and the stratum corneum occurred.
Uehara M, Ofuji S. The Morphogenesis of Pustulosis Palmaris et Plantaris. Arch Dermatol. 1974;109(4):518-520. doi:10.1001/archderm.1974.01630040028005