Membranous lipodystrophy: primary idiopathic type.

A 20-year-old woman had a pea-sized, tender subcutaneous nodule on the leg. Histopathologically, the panniculus showed multiple microcysts lined by membranes and light brown granules in the histiocytes. Histochemical studies of the membranes of the microcysts and the granules in the histiocytes indicated that they were composed of ceroid. Electron microscopy revealed that the membrane of the microcyst was composed of electron-dense areas of a regular 18.6 nm lamellar array and reticulated vacuolated areas suggestive of degenerating fat cells of unknown origin. Membranous lipodystrophy has been associated with many local and systemic diseases, but it may be idiopathic, as in our patient.