To determine the clinical and electrophysiological characteristics of chronic motor axonal neuropathy (CMAN) and identify the associated similarities and differences between CMAN, acute motor axonal neuropathy (AMAN), and motor neuropathy secondary to amyotrophic lateral sclerosis.
The study described clinical and electrophysiological features of five patients with CMAN and compared with 20 AMAN patients, 42 amyotrophic lateral sclerosis patients and 41 healthy controls. To compare the distribution of different nerve involvement in the same limb, split ratio was introduced. Split ratio of upper limb = amplitude of compound muscle action potential abductor pollicis brevis (APB)/amplitude of compound muscle action potential abductor digiti minimi, and split ratio of lower limb = amplitude of compound muscle action potential extensor digitorum brevis/amplitude of compound muscle action potential abductor hallucis.
Chronic motor axonal neuropathy patients manifested lower motor neuron syndrome with positive IgG anti-monosialoganglioside antibodies and good outcome. The CMAN patients shared similar clinical manifestation with AMAN patients except for disease course and higher Medical Research Council scores. Compared with healthy controls, the split ratio of lower limb was higher in both CMAN and AMAN, despite comparable split ratio of upper limb. There was significant difference between CMAN group and amyotrophic lateral sclerosis group in nerve involvement presented as split hand and split leg signs in amyotrophic lateral sclerosis and reverse split leg sign in CMAN.
Chronic motor axonal neuropathy associated with monosialoganglioside might be a “mild” AMAN with chronic onset by similar clinical and electrophysiological features. There was a unique pattern of nerve involvement presenting as reverse split leg sign in both CMAN and AMAN.