Unmyelinated fibers in sural nerve biopsies of chronic inflammatory demyelinating polyneuropathy.

Seven patients aged 29 to 76 years with various clinical subtypes of chronic inflammatory demyelinating polyneuropathy (CIDP) were investigated. Sural nerve biopsies were performed between 7 months and 19 years after onset of disease. Quantitative electron microscopy revealed involvement of primary unmyelinated fibers (UF) in all cases. When compared with age-matched controls from the literature and two controls of our own, there was an increase of degenerating primary UF in all cases, a definite decrease of density per mm2 or number per nerve after subtraction of regenerates of myelinated and unmyelinated fibers in five cases, an increase of denervated Schwann cell complexes of the unmyelinated type in three cases, and an increased incidence of a high ratio (greater than or equal to 3) of primary UF per Schwann cell complex in five cases. Presumably due to the small number and heterogeneity of cases, the results did not correlate with type and duration of CIDP, but were obviously influenced by the degree of demyelination. The possible causes of UF damage in CIDP are discussed.