Nerve fibre size in the carpal tunnel syndrome

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Abstract
Alterations in nerve fiber size and related findings are reported in a case of carpal tunnel syndrome, severe on the right side and mild on the left. At autopsy both median nerves were dissected distally from the level of the upper arm. For about 1 cm above the superior margin of the flexor retinaculum on the right side the nerve was enlargedto nearly twice the size of the nerve higher in the forearm. Upon dividing the flexor retinaculum constriction of the nerve could be seen for the length of the carpal tunnel. The nerve was more normal in size distal to the retinaculum. Specimens were taken from the following sites on both sides and stained by a modified Weigert method: (a) median nerve trunk at mid-forearm level, 1 cm above the flexor retinaculum and under the retinaculum; (b) second, third and fourth palmar digital nerves; and (c) the branch to the left thenar muscles. The perineurium and endoneurial connective tissue was considerably thicker in sections taken from under the retinaculum on both sides but more so on the right. Endoneurial connective tissue in relationship to the digital nerves shwoed an increase on the right as compared with the left side. Fiber size was somewhat reduced 1 cm above the retinaculum on the right and was significantly reduced under the retinaculum on both sides, particularly the right. When compared with the left, the digital nerves on the right showed a reduction in fiber size but these fibers were greater on both sides than under the retinaculum. In conjunction with these findings conduction velocity on the right was greatly slowed distal to the wrist and was below the lower limit of the normal range in the forearm.