Morton's metatarsalgia. Light and electron microscopic observations and their relation to entrapment neuropathies.

The dissected plantar nerves of 105 patients with clinical symptoms of Morton's disease were examined under light and electron microscopy. Of the 105 cases, 75 showed characteristic neuronal lesions; in the others different pathologic substrates responsible for the clinical symptoms could be demonstrated. The nervous lesions are characterized by: 1. Thickening of the walls of the endoneurial vessels produced by multiple layers of basement membranes. 2. Edema and sclerosis of the endoneurium. In the electron microscope the endoneurium was filled by deposits of fibrils with a tubular substructure and a diameter of 100-110 A. 3. Thickening of the perineurium. 4. Degeneration of the nerve fibers without signs of wallerian degeneration or obvious reactive Schwann's cell hyperplasia. The possible pathogenetic mechanisms of Morton's disease and some clinical problems are discussed.