The authors report a case of localized hypertrophic mononeuropathy involvin
g the femoral nerve in a 20-year-old woman referred because of progressive
weakness and atrophy of the left thigh. MRI showed an enlarged femoral nerv
e and biopsies of fascicles displayed a concentric pattern of cells resembl
ing an onion bulb. These cells were positive for epithelial membrane antige
n immunostaining and had an incomplete basal lamina.