Perineurium contributes to axonal damage in acute inflammatory demyelinating polyneuropathy

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Abstract
Objective: To assess if axonal damage in severe acute inflammatory demyelinating polyneuropathy (AIDP) correlates with the appearance of epiperineurium in nerve trunks. Background: Increase of endoneurial fluid pressure in nerve trunks possessing epiperineurium may be an important mechanism of axonal damage in AIDP. Methods: A 79-year-old man had a 2-day history of acroparesthesias and ascending paralysis culminating in quadriplegia, bilateral facial palsy, and mechanical ventilation. Five intravenous immunoglobulin cycles were given without response. He died on day 60. Electrophysiologic studies (days 4, 17, and 50) initially showed normal nerve conduction velocities with further slowing, progressive attenuation of compound muscle action potentials, and profuse denervation. The authors studied the preforaminal anterior and posterior L3 and L5 spinal roots, third and fifth lumbar nerves and their branches, and femoral and sural nerves. Results: Density of myelinated fibers was preserved in L5 ventral and dorsal roots and reduced in sural nerve. Mild de-remyelination was observed in lumbar roots. In both lumbar nerves and their branches, there were extensive de-remyelination and centrofascicular or wedge-shaped areas with marked loss of large myelinated fibers. Axonal degeneration was the predominant lesion in sural nerve. Conclusion: The presence of epiperineurium correlates with a drastic change of pathology with superimposed ischemic lesions and distally accentuated axonal loss, suggesting that endoneurial fluid pressure increase could cause axonal damage in AIDP.