INTRODUCTION AND BACKGROUND
For decades, the specific dermatoses of pregnancy represented a confusing group of overlapping entities, understood largely through anecdotes and case reports. However, more recent reviews have simplified and condensed the list of pregnancy-specific dermatoses (Table 27.1). For example, impetigo herpetiformis is now generally recognized as pustular psoriasis, perhaps induced by the relative hypocalcemia of pregnancy (see Ch. 8). Also, prurigo annularis, first reported in 1941 (without histology or laboratory information), and linear IgM disease of pregnancy (described in 1988) have not been subsequently reported yet are frequently perpetuated in reviews.
Much of the confusion can be dispelled by reviewing the original articles: Besnier (1904) first used the term “prurigo gestationis” to include all patients with pregnancy-related dermatoses, other than those with pemphigoid gestationis. Costello (1941) subsequently referred to these patients as “prurigo gestationis of Besnier” and estimated an incidence of 2% of all pregnancies. Bourne (1962) characterized a subset of patients with intensely pruritic papules or urticarial plaques that tended to appear during the later part of the third trimester, coining the term “toxaemic rash of pregnancy”. Initial lesions typically developed within the abdominal striae of short women who experienced excessive weight gain during pregnancy. However, he offered no histopathologic or laboratory details.
Spangler et al. (also 1962) reported on a series of women with intensely pruritic, widely scattered, excoriated papules. Initial onset was during the second or third trimester and all patients suffered recurrences during subsequent gestations. The hallmarks of Spangler’s cases were biochemical: elevated urinary human chorionic gonadotropin (HCG), decreased plasma hydrocortisone, and decreased serum half-life of hydrocortisone. Liver function tests and histopathology were not reported, and immunofluorescence (IF) was not yet available. Most notably, Spangler’s papular dermatitis was associated with high fetal wastage, a finding now thoroughly discredited.
Nurse (1968) cited all of the above literature but ignored it, dividing patients with (non-pemphigoid gestationis) pregnancy eruptions into “early” and “late” forms. The late papular/urticarial form clearly overlapped with Bourne’s “toxaemic rash of pregnancy”, and has since been described as “pruritic urticarial papules and plaques of pregnancy” (PUPPP), “toxic erythema of pregnancy”, and, most recently, “polymorphic eruption of pregnancy” (PEP). Nurse’s “early-onset” patients and Spangler’s “papular dermatitis” patients were undoubtedly drawn from the same clinical spectrum, and subsequently these entities were reclassified as forms of “prurigo of pregnancy” (see Table 27.1).
Pruritic folliculitis of pregnancy was added to the list of pregnancyspecific diseases in 1981, yet all six of the original patients were thought to have papular dermatitis clinically. They were classified as having a different entity based solely upon shared histologic features, that is, sterile folliculitis. In spite of their clinical similarity to the patients reported by Spangler, none had appropriate biochemical investigations. In 1998, an adaptation of the Holmes and Black classification scheme (1983) was published and listed pruritic folliculitis as a variant of prurigo of pregnancy (see Table 27.1).
Introduction of the term “atopic eruption of pregnancy (AEP)” represents the most recent revision to the classification of dermatoses of pregnancy. Based upon an analysis of over 500 pregnant women with pruritus, significant overlap, both clinical and histologic, was noted amongst those patients with the diagnoses of prurigo of pregnancy, pruritic folliculitis of pregnancy, and eczema in pregnancy (~50% of the patients in this series). AEP was thought to be a useful diagnostic term that encompassed these three disorders and reminded the clinician that the eczema was more likely to be of new onset as opposed to a flare of previously diagnosed atopic dermatitis.
Because of the lack of primary lesions, intrahepatic cholestasis of pregnancy (ICP) had long been omitted from the list of pregnancy dermatoses. However, failure to appreciate ICP in a pregnant woman with widespread excoriations or even prurigo nodularis surely, in retrospect, accounts for some of the confusion in terminology. Furthermore, ICP is the most important diagnosis to exclude in a pregnant patient with pruritus, as it is associated with significant fetal risk (see below).
Table 27.1 Classification of the dermatoses of pregnancy. The preferred terms are in bold.