Activity-dependent hyperpolarization and conduction block in chronic inflammatory demyelinating polyneuropathy

Abstract

Voluntary activity produces activity‐dependent hyperpolarization of the active motor axons. The present study investigated whether this hyperpolarization produces conduction block in chronic inflammatory demyelinating polyneuropathy (CIDP). Studies were performed in 10 healthy control subjects, 7 patients with CIDP, and 3 patients with multifocal motor neuropathy. The compound muscle action potential (CMAP) of the abductor pollicis brevis was recorded in response to supramaximal stimuli to the median nerve at the wrist, alternating with measurements of axonal excitability. After a maximal voluntary contraction for 60 seconds, the amplitude of the maximal CMAP was significantly reduced in symptomatic CIDP patients by 40%, but there were only slight changes in the CMAPs of healthy controls, asymptomatic CIDP patients, and multifocal motor neuropathy patients. In symptomatic CIDP patients, the activity‐dependent conduction block paralleled the activity‐dependent hyperpolarization and was presumably precipitated by it. In these patients, the safety margin for impulse conduction was estimated to be about 12%. Activity‐dependent conduction block may be clinically important in chronic demyelinating diseases and can be demonstrated electrophysiologically if testing occurs across pathological sites. Ann Neurol 2000;48:826–832

Nerve excitability changes after intravenous immunoglobulin infusions in multifocal motor neuropathy and chronic inflammatory demyelinating neuropathy

“…Patients with MMN also did not differ from normals, except for 1 ms-SRC ratio. These results confirmed previous studies showing nearly (but not "strictly") normal excitability profiles in territories unaffected by conduction blocks in MMN [27,28].…”

Evaluation of Na+/K+ pump function following repetitive activity in mouse peripheral nerve

“…Activity-dependent hyperpolarization may, however, impair conduction in demyelinated axons (Bostock and Grafe, 1985;Kiernan et al, 1996a). Demyelinated motor axons are especially prone to activitydependent conduction block (Cappelen-Smith et al, 2000, 2003Kaji et al, 2000) as they express less inward rectification than sensory axons Kiernan et al, 2004;Lin et al, 2002). Reducing Na + /K + pump activity improves conduction in demyelinated axons in experimental (Kaji and Sumner, 1989a,b) and clinical trials (Kaji et al, 1990).…”

Altered axonal excitability properties and nerve edema in POEMS syndrome

“…The pattern of excitability changes are different from those in chronic inflammatory demyelinating polyneuropathy (CIDP); previous reports on CIDP have shown that compared with normal subjects, strength-duration time constant was significantly shorter, and in the recovery cycle, CIDP patients had less refractoriness, supernormality and late subnormality than healthy controls (Cappelen-Smith et al, 2000;Sung et al, 2004). Current-threshold relationships did not show significant changes.…”