Multiple system atrophy (MSA) is a neurodegenerative disease; dysautonomia and extrapyramidal syndrome are the cardinal symptoms. Differential diagnosis with other parkinsonism is difficult; it’s required an ideal diagnosis test. The degeneration of Onuf`s nucleus, exclusively in MSA, might suggest that presence of denervation of the anal sphincter may be taken into account as diagnostic criteria for AMS. We conducted a systematic review to establish the clinical utility of anal sphincter electromyography (AS-EMG) in the differential diagnosis of AMS with other parkinsonian syndromes. 17 studies was included and was analyzed the results of AS-EMG in patients with MSA. Of these, 11 studies were analytical and compared patients with MSA and other parkinsonisms. The remaining studies were descriptive. The duration of motor unit potentials (MUP) is significantly higher in patients with MSA compared with other parkinsonism with a cut-off > 13 ms; the operating characteristics of this parameter are potentially useful. Only one study found significant differences in the percentage of polyphasic MUP, which had a clinically useful sensitivity and specificity when the cutoff is greater than 60%. The other studies reported no statistically significant differences between parkinsonism. The available literature points to the potential usefulness of EMG-EA in the differential diagnosis of parkinsonism other AMS, but more studies need to be conducted to address the existing methodological limitations.