In vitiligo, some areas are harder to repigment then others. For example areas such as ankles, hands and feet don't respond as well to UV treatment as do areas such as the face or neck. A team of researchers at the University of Cairo attempted to determine what is the cause of these differences.
They prelevated skin biopsies before and after PUVA therapy and observed that the chemical changes were similar in both regions but repigmentation was slow to occur on hands and feet. Other areas responded positively and showed signs of repigmentation.
The factors thought to have an influence are:
- the lower melanocyte density in acral regions (limbs and other extremities)
- lower number of melanocyte stem cell reservoirs
Esmat, S.M., El-Tawdy, A.M., Hafez, G.A., Zeid, O.A., Abdel Halim, D.M., Saleh, M.A., Leheta, T.M. and ElMofty, M. (2012), Acral lesions of vitiligo: why are they resistant to photochemotherapy?. Journal of the European Academy of Dermatology and Venereology, 26: 1097–1104. doi: 10.1111/j.1468-3083.2011.04215.x