A 35-year-old woman from Bolivia was in the 37th week of a complication-free second pregnancy. She presented with asymptomatic diffuse areas of hyperpigmentation that had appeared progressively on the lateral and posterior aspects of her thighs and legs to form 2 abrupt, totally symmetric lines on the medial portion of both extremities. The lines formed a clear boundary between the hyperpigmented and normal skin (Fig. 1). Of note also was the presence of the linea alba and acanthosis nigricans. The findings led to a diagnosis of type B pigmentary demarcation lines associated with pigmentary changes in pregnancy.

Figure 1

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Pigmentary demarcation lines are abrupt transition lines that separate areas of hyperpigmentation from areas of normal skin. They were described by Matsumoto in 1913. Their etiology and pathogenesis are unknown, but their distribution appears to follow Voigt lines and could correspond to differences in melanocyte distribution, probably influenced by genetic and hormonal factors. There are 8 subtypes of pigmentary demarcation lines but the most common ones are type B lines associated with pregnancy. They are mostly found in patients with high Fitzpatrick skin types and they affect the lower extremities. Diagnosis is clinical and the lines typically appear during the third trimester and disappear postpartum.