INTRAMYELINIC EDEMA: AN ELEMENTARY PATHOLOGICAL LESION IN CIDP

Abstract

Pathological abnormalities of sural nerve biopsies from patients affected by chronic inflammatory demyelinating polyneuropathy (CIDP) include segmental demyelination, inflammatory infiltrates, axonal degeneration, subperineurial edema and Schwann cell proliferation.There are few reports in the literature (Waddy '89, Sabatelli '96) describing edema of the myelin sheath as an additional pathological feature of CIDP. This peculiar abnormality is a prominent finding in several experimental toxic and compression neuropathies. In 1993 Tatum described Intramyelinic Edema in experimental allergic neuritis induced by systemic passive transfer of human IgM anti‐myelin‐associated glycoprotein, and suggested that this change may play a role in the pathogenesis of demyelination.In order to establish whether intramyelinic edema may represent an elementary pathological lesion in human peripheral neuropathies, we reviewed morphological data of sural nerve biopsies from 46 CIDP patients admitted to our Institute from 1988 to 2001 and we compared them with findings from patients affected by other neuropathies.IE was observed in 6 patients with CIDP, but in none of the 500 patients affected by neuropathies of different etiology. In two out of the six patients the neuropathy was associated with IgM‐paraprotein, without anti‐MAG activity. IE was a prominent feature in only one patient while in the remaining patients it was confined to sporadic fibers. In one patient with a mild form of CIDP, IE was the only pathological finding. In the remaining patients it was associated with segmental demyelination and axonal loss.Our findings show that although IE is observed in only a minority of CIDP patients (13% of our series), this pathological finding may be considered a specific abnormality of inflammatory demyelinating neuropathies. We suggest that axonal shrinkage, which is invariably associated with IE, may represent a mechanism of loss of function in CIDP, in addition to segmental demyelination and axonal loss.