Is peripheral neuron degeneration involved in multiple system atrophy? A clinical and electrophysiological study

Lower motor neuron lesions are not among the characteristic features of multiple system atrophy (MSA), although electromyography (EMG) and autopsy studies revealed peripheral neuron abnormalities in some cases of MSA. The aim of the study was to evaluate subclinical involvement of the peripheral neuron in MSA using EMG and electroneurography (ENG).

48 patients with clinically probable MSA (mean age 60.6 years; 67% males) were included in the study and divided into subgroups, with predominant cerebellar (MSA-C) and parkinsonian signs (MSA-P).

ENG in ulnar, peroneal and sural nerves and EMG of the first interosseus dorsal and tibial anterior muscles were performed.

Abnormal ENG in one nerve was recorded in 20.8% of patients, and in two nerves in another 20.8% of patients. The most frequent and significant findings were decreased compound motor action potential amplitudes in the ulnar nerve in the overall MSA group as well as in the MSA-P type as compared to controls. Abnormalities suggesting reinnervation was observed in 43 of 96 examined muscles (44.7%). In individual cases, neurogenic features were recorded in one muscle in 31.2% of patients and in two muscles in 29.1% of patients.

Subclinical axonopathy in MSA is not frequent and is more pronounced in MSA with predominant parkinsonian signs. In MSA, neurogenic EMG abnormalities in muscles are more frequent than peripheral nerve lesions and as evidenced by increased motor unit potential amplitudes, could be considered a sign of anterior horn cell involvement and a hallmark of the "continuum" of neurodegeneration in MSA.