Linear hyperpigmentation along the Blaschko's line: A clinicopathologic study

Background: Many pigmentary disorders can be manifested as linear streaks of hyperpigmentation, along the Blaschko's line. These include progressive cribriform and zosteriform hyperpigmentation (PCZH) and linear and whorled nevoid hyperpigmentation (LWNH). There have been debates on the universally accepted diagnostic criteria differentiating these disease entities. Objective: To determine the clinicopathologic characteristics of hyperpigmentation along the line of Blaschko and to examine the acceptability of PCZH or LWNH criteria as a diagnostic tool for differentiating these diseases. Methods: A retrospective study was conducted on 13 patients who presented with linear hyperpigmentation along the Blaschko's line. The patients' clinicopathologic characteristics were analyzed and matched with the PCZH/LWNH diagnostic criteria. Results: Age of onset widely ranged from birth to 61 years, but predominantly before the age of 4 years. The male-female ratio was 1:1.2. Trunk was the most common site of involvement. Histologic examination commonly showed a basal layer hyperpigmentation in all patients and pigmentary incontinence was observed in 2 patients. Four patients who satisfied all the diagnostic criteria for PCZH also fulfilled the diagnostic criteria for LWNH, except for the timing of onset. An additional 4 patients satisfied all the diagnostic criteria for LWNH and also fulfilled the diagnostic criteria for PCZH, except for the timing of onset. Excluding the age of onset criteria, the other 3 patients fulfilled both diagnostic criteria for PCZH and LWNH. Conclusion: These results demonstrate that PCZH and LWNH should not be considered as a different disease entity and that supports the idea that these are part of the same disease spectrum.