To the Editor:
We thank Drs. Zvulunov and Metzker for their comments on our article. The differentiation between neurofibromatosis (NF) and giant pigmented nevus (GPN) is indeed not possible with light microscopy becauseGPN may have a neuroid appearance. Like Drs. Zvulunov and Metzker, we do not know any histochemical technique that is helpful in the differentiation between NF and GPN.
However, as described in our article, electron microscopy is of primary importance because it differentiates between Schwann cells and nevus cells and thus between NF and GPN. Reliable ultrastructural criteria for Schwann cells are
(l) spindle cells with long, thin, interwinding processes;
(2) basal lamina covering processes and cell bodies; and
(3) long-spacing collagen (Luse bodies), which are never seen in GPN.