Hypertrophic mononeuropathy. A report of two cases and review of the literature.

Two cases of hypertrophic mononeuropathy were studied. This entity is characterized grossly by focal enlargement of a single peripheral nerve, and microscopically by loss of nerve fibers, fibrosis, and formation of numerous onion bulbs. Our cases were diagnosed by exploratory surgery, biopsy, and light microscopy. Electron microscopic evaluation was performed in one case. Recognition of this entity by the surgical pathologist is important, so that it can be distinguished from generalized forms of onion bulb neuropathies, most of which give a much less favorable long-term prognosis. Hypertrophic mononeuropathy has usually resulted in irreversible local neurologic deficit but, unlike the polyneuropathies, in all the previously reported cases (as well as in our two cases to date) it has remained a localized process.