Pruritic urticarial papules and plaques of pregnancy (PUPPP), also known as polymorphic eruption of pregnancy (PEP) is the most common gestational dermatosis.[1] It is a benign, pruritic, inflammatory skin disorder, characterized by a polymorphous clinical presentation, normal laboratory tests, and negative direct immunofluorescence. PUPPP usually affects primigravidas in their third trimester of pregnancy, less frequently in the immediate postpartum period, and has no tendency for recurrence in subsequent pregnancies. Lawley et al. first described this entity in 1979, based on the initial clinical findings of urticarial papules and plaques, developing within striae distensae.[2] To encompass the later polymorphous features, also described in this condition, the term “polymorphic eruption of pregnancy” has been suggested and is now similarly accepted. 

The cause of pruritic urticarial papules and plaques of pregnancy is still unknown, although various etiological theories have been proposed, including abdominal distension, hormonal changes, placental factors and the role of fetal DNA in skin lesions of patients with PUPPP.[3] In a study of Holms and al. the eruption was thought to have developed in 90% of patients, as a consequence of damage to connective tissue within striae.[4] Therefore suggestions have been that rapid, late stretch­ing of abdominal skin, occurring with a high frequency in multiple pregnancies, may lead to connective tissue damage and that the exposure of antigens within collagen could elicit an allergic-type reaction, resulting in the initial appear­ance of the eruption in striae. Additionally, there are suggestions that peripheral chimerism (deposition of fetal DNA), which occurs particularly during the third trimester, and favors skin with increased vascularity and damaged collagen, could be subsequently the target of immune reactivity.[5] The mechanism by which lesions become generalized is also unclear. An inflammatory response is thought to be promoted by cross-reactivity to collagen in otherwise normal-appearing skin. An immune tolerance mechanism during subse­quent pregnancies might prevent recurrence.[3] High levels of progesterone, especially if multiple gestations and increased progesterone receptor immunoreactivity have been demonstrated in patients with PUPPP [6]. Another hypothesis centers on fibroblast proliferation in the maternal skin, induced by a placental hormonal-type substance.[7]

The reported incidence of pruritic urticarial papules and plaques of pregnancy in the literature is 0,5% in single pregnancies, 2.9 to 16% in twin pregnancies and 14 to 17 % in triplet pregnancies.[8][9] It is seen predominantly in primigravidas women and tends not to relapse in later pregnancies. Reports have linked excessive maternal weight gain and increased newborn birth weight in association with PUPPP. Patients affected were interestingly Rh-positive in a study of Ghazeeri and colleagues, and in 89% of them, conception was the product of in vitro fertilization.[10] Relative to fetus gender, a male to female ratio of 2 to 1 has been reported. Usually, there is no family history of this type of eruption and studies revealed, neither an autoimmune diathesis nor a specific HLA type association.[4]

Biopsy specimens from lesional skin reveal nonspecific findings. In early pruritic urticarial papules and plaques of pregnancy lesions, there is epidermal and upper dermal edema, and occasionally focal mild spongiosis, with a deeper dermal lymphohistiocytic perivascular infiltrate,[11] which may resemble arthropod bite reactions. The lymphocytic infiltrate is often composed of T-helper lymphocytes with an admixture of a variable number of eosinophils and neutrophils. In the resolving stage of PUPPP, there is acanthosis with hyperkeratosis and parakeratosis. Ghazeeri and al. reported epidermal changes commonly seen in the biopsies taken from patients who had lesions with various morphologies including papulovesicular rash, target-like lesions, and eczematous lesions.[10] Direct immunofluorescence of lesional skin is usually negative. Nevertheless, minimal nonspecific granular deposition of IgM, C3 or IgA along the dermal-epidermal junction or blood vessels had also been reported.[8] Indirect immunofluorescence investigations for circulating IgG antibodies shows almost always negative results. But in one study the presence of circulating IgM anti-basement membrane zone, in 5 from 111 cases had been reported.[12]