Multimodal evoked potentials in multiple system and late onset cerebellar atrophies.

Forty subjects were clinically examined using scales for cerebellar, pyramidal, parkinsonian, and mental status and by quantitative evaluation of neuroimages. The patients were classified into two groups: cerebellar-plus and "pure" cerebellar syndromes. Patients with "pure" cerebellar syndrome were diagnosed as autosomal dominant cerebellar ataxia III (ADCA III) or "pure idiopathic" late-onset cerebellar ataxia (ILOCA) in this series. Patients with cerebellar-plus syndrome were diagnosed as multiple system atrophy (MSA), subclassified as either ILOCA-plus, ADCA I, ADCA II or autosomal recessive LOCA. We have used visual (VEP), brainstem auditory (BAEP) and somatosensory (SEP) evoked potentials in order to establish their diagnostic validity. Cerebellar-plus syndrome and "pure" cerebellar syndrome showed overlapping VEP, BAEP and SEP abnormalities. VEP P100 latency, however, shows a certain ability to differentiate between the two groups (p = 0.08) and appears useful in distinguishing between sporadic cerebellar-plus syndromes (MSA or ILOCA-plus) and "pure" cerebellar syndromes (p < 0.02). The incidence of prolonged N9-N13 latency was significantly higher in the latter subgroup (p < 0.04) as well. Within cerebellar-plus syndromes, VEP, BAEP and SEP abnormalities were more frequent in inherited cases (ADCA I and II, along with autosomal recessive LOCA) than in sporadic ones. The most apparent differences were a higher incidence of abnormal BAEPs at brainstem level (p < 0.002), and of both peripheral and possible central SEP impairment in hereditary cerebellar-plus syndrome than in sporadic cerebellar-plus syndrome (p < 0.03). EP investigation is useful to a certain extent in differentiating between some variants of LOCA.