Behavior of melanocytes in reticulate acropigmentation of Kitamura.

Four patients with reticulate acropigmentation of Kitamura (RAPK) had reticulate pigmentation that was slightly depressed below the skin surface. Histologic findings revealed epidermal atrophy, elongation of the rete ridges with large amounts of melanin, and an increased number of dopa-positive basal melanocytes. Electron microscopic findings showed many melanosome complexes within the keratinocytes, dendrites filled with numerous melanosomes, and some melanosome complexes within the melanocytes. It is concluded that the hyperpigmentation of RAPK is due to increased number of active melanocytes and to increased transfer of melanosomes to surrounding keratinocytes.