AIDP is characterized by lymphocytic (mainly T cell) and macrophage infiltration and associated segmental demyelination, which affect nerve roots, plexi, and proximal portions of the nerves, which are more myelinated [10, 11]. Complement activation has been suggested to play an early role, as deposition of complement activation marker C3d and terminal complement complex C5b-9 on the surface of Schwann cells and myelin degeneration were shown to precede macrophage infiltration in patients who succumbed in early stage of AIDP [12].

On the other hand, postmortem findings in AMAN subtype may show Wallerian degeneration of the motor axons; presence of macrophages within the periaxonal space, which surround or displace the axons; and intact myelin sheath [13]. Some of the AMAN patients with fatal paralysis have had minimal axonal degeneration in the postmortem study consistent with functional impairment of axonal electrical conduction in these cases [13]. Axonal degeneration of the motor and sensory nerves is the hallmark of the neuropathology in AMSAN [13]. Because of the benign clinical course of MFS, the pathological studies are limited. Although segmental demyelination is reported in a patient with MFS [14], the patient more likely had AIDP and associated ophthalmoplegia.

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