Background: The present case is an example of hypertrophic inflammatory neuropathy (HIN). This entity is a rare tumor-like, chronic inflammatory, focal or multifocal, mainly demyelinating neuropathy of unknown origin, most frequently involving the brachial plexus.
Case description: The authors describe a 67-year-old man presenting with a nodular mass in his right supraclavicular fossa. A nodular mass grossly resembling a schwannoma originating from a single nerve fascicle was surgically removed from the right C6 spinal nerve. Histologically, endoneurial edema, fibrosis, focal chronic inflammation, and extensive "onion bulb" formation were seen. Electron microscopy studies and immunohistochemistry proved that the onion bulb-forming cells were schwannian in nature and that the whorls of onion bulbs surrounded a generally demyelinated axon. Three months following surgery the patient developed acute painless paralysis of his right biceps brachii muscle that rapidly reversed; after that he remained neurologically asymptomatic. MRI revealed multiple fusiform mass lesions involving the brachial plexus bilaterally. Electrophysiologic studies demonstrated a bilateral, asymmetrical, mainly demyelinating neuropathy involving the brachial plexus; they failed to reveal any abnormality suggestive of generalized neuropathy.
Conclusion: HIN is different from other focal tumor-like neuropathies and in particular from localized hypertrophic neuropathy (LHN).