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  1. R T Woolf, specialist registrar, dermatology 1,
  2. Alya Abdul-Wahab, specialist registrar, dermatology1
  1. 1St John’s Institute of Dermatology, Guy’s and St Thomas’ NHS Foundation Trust, London SE1 7EH, UK
  1. Correspondence to: R T Woolf richard.woolf{at}gstt.nhs.uk

A 33 year old woman at 40 weeks’ gestation of her first pregnancy presented with an itchy rash. This had started 14 days earlier with a few red patches on her lower abdomen but extended to involve her thighs and upper arms. The rash was increasingly pruritic. She reported gluten insensitivity (coeliac disease not confirmed) and had no dermatological or atopic history. The pregnancy had been uneventful until this point. She took no regular drugs and had not used any topical preparations. Her rash on clinical examination was as shown in the photograph.⇓

Questions

  • 1 How would you describe the rash?

  • 2 What is your diagnosis?

  • 3 What other diagnoses should be considered?

  • 4 What investigations could you consider?

  • 5 How would you treat this patient?

Answers

1 How would you describe the rash?

Short answer

An erythematous papular rash has spared the periumbilical region but in places has formed areas of confluent urticated erythema, especially at the striae distensae.

Long answer

An erythematous papular rash has spared the periumbilical region but in places has coalesced to form areas of confluent urticated erythema, especially at the striae distensae (“stretch marks”). The linear hyperpigmentation along the mid-line of the abdomen, known as the linea nigra, is a physiological phenomenon commonly seen in pregnancy.1

2 What is your diagnosis?

Short answer

A papulo-urticarial rash developing in the third trimester of a first pregnancy, originating within the striae distensae and sparing the umbilicus, is typical of polymorphic eruption of pregnancy (PEP).

Long answer

PEP affects about one in 160 pregnancies and commonly occurs in the third trimester (91% of cases) of primigravid women (73%).2 3 It classically presents with polymorphic erythema, papules, or vesicles (that can be urticated) that arise within the striae distensae of the abdomen and spare the peri-umbilical region, face, and acral sites.4 Less commonly the rash can become generalised, and rarely the vesicles form larger bullae.3 …

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