Persistent multifocal pseudo‐conduction blocks in vasculitic neuropathy without antiganglioside antibodies

Abstract

A woman presented with severe multifocal acute axonal neuropathy due to necrotizing vasculitis. Six years later, electrophysiological examination revealed features suggestive of persistent conduction block (CB) with increased temporal dispersion (ITD) affecting the right median and tibial nerves. A clinical case characterized by multifocal CBs that were observed several years after an initial episode of vasculitic neuropathy was recently reported. The occurrence of CBs paralleled clinical deterioration and was attributed to superimposed antiganglioside antibody‐mediated demyelination. In contrast, our patient was clinically stable and did not have antiganglioside antibodies. Nerve conduction studies showed pseudo‐CBs rather than true CBs. We suggest that pseudo‐CBs with ITD can reveal heterogeneous axonal regeneration as a sequel of a severe multifocal vasculitic neuropathy. This condition should be distinguished from the occurrence of pseudo‐CB in the acute phase of vasculitis or from superimposed immune‐mediated demyelination. Muscle Nerve 40: 290–293, 2009

A decline of compound muscle action potential (CMAP) amplitude between proximal and distal nerve stimulation, suggestive of motor conduction block (CB), can be encountered in acute vasculitic neuropathy within hours or days of symptom onset.7-9, 13 This finding likely corresponds to the fact that nerve conduction is focally interrupted at the level of axonal infarction secondary to necrotizing vasculitis, while axons remain excitable distal to the lesion for several days. Such “pseudo‐CB” is transient and disappears as Wallerian degeneration progresses in the distal segment.2, 8

Recently, persistent multifocal CBs were reported in a patient with vasculitic neuropathy, occurring in the context of cryoglobulinemia and autoimmune thyroiditis.11 This finding was attributed to the presence of IgM antiganglioside antibodies, leading to superimposed immune‐mediated demyelination. In this report we show that apparent persistent CBs can be observed late in the course of vasculitic neuropathy in the absence of antiganglioside antibodies, likely due to heterogeneous axonal regeneration rather than to segmental demyelination.