Histiocytosis X: diagnosis by electron microscopy.

The three histiocytosis X diseases are often initially misdiagnosed because of their frequently slow and insidious onset. Cutaneous lesions are commonly seen and are often the initial manifestation. The atypical histiocytes in all clinical types of histiocytosis X contain characteristic intracytoplasmic granules that can be seen with the electron microscope. Skin biopsy is thus a simple and rapid method for confirming the diagnosis of histiocytosis X.