Distribution, clinical correlates and significance of axonal loss and demyelination in chronic inflammatory demyelinating polyneuropathy

Abstract

The distribution of axonal loss and demyelination has rarely been studied in chronic inflammatory demyelinating polyneuropathy (CIDP). Whether electrophysiological parameters may represent clinically relevant biomarkers of disease activity in the disorder remains uncertain. The purpose of this study was (i) to ascertain the distribution of electrophysiological motor abnormalities to optimize the diagnostic utility of nerve conduction studies and (ii) to establish electro-clinical correlations in an attempt to find the potential parameters that could represent adequate biomarkers of disease activity and prognosis. The clinical and electrophysiological motor features of 31 prospectively recruited patients with clinically stabilized CIDP were analysed. Axonal loss predominated in the lower limbs, but demyelination was more common in the upper limbs. About 50% of all demyelinating abnormalities were detected in asymptomatic regions. Presence of weakness correlated with abnormal compound muscle action potential (CMAP) and abnormal motor nerve conduction velocity (MNCV). Degree of weakness and functional scores only consistently correlated with CMAP amplitudes. CMAP abnormality correlated with abnormal MNCV, abnormal distal motor latency (DML) and presence of conduction block (CB). However, although CMAP amplitudes also correlated with MNCVs and DMLs in raw values, they did not relate to the degree of CB. Electrodiagnosis of CIDP is optimized by extensive testing of upper limb nerves and of asymptomatic regions. Raw value CMAP amelioration and MNCV normalization may be adequate markers of clinical improvement in CIDP. Similarly, raw value MNCV and DML amelioration, as well as CB reversal may represent adequate prognostic markers.