Visual evoked potentials and brain stem auditory potentials in Friedreich's ataxia--a longitudinal study

Evidence that Charcot-Marie-Tooth disease with tremor coincides with the Roussy-Levy syndrome

Four members of a family with consanguineous relationships, the proband and his three children (2 sons and 1 daughter) are affected with Familial Spastic Ataxia and with Ehlers-Danlos' Syndrome with platelet aggregation dysfunction. In the four cases, this exceptional association appears remarkably homogeneous both in clinical and laboratory studies. The two syndromes are of dominant-autosomic transmission and probably originated in a new mutation which presumably maintained a genetic linkage. Spastic ataxia is characterized by a precocious onset and a slow evolution. The first-born son shows a dominant pyramidal syndrome with mild ataxia suggesting that it is a transitional form of familial spastic paraplegia. The Ehlers-Danlos syndrome pertains to form II or “mitis” with moderate skin hyperelasticity and joint hypermobility. The abnormal platelet aggregation curves have the same profile in all the patients. The first-born son also presents a mitral valve prolapsus as we may find either in Ehlers-Danlos syndrome or in spastic ataxia.

Electrophysiological features in patients and presymptomatic relatives with spinocerebellar ataxia type 2

Motor and sensitive nerve conduction studies, visual (VEP), brainstem auditory (BAEP) and somatosensory (SSEP) evoked potentials in 82 patients with spinocerebellar ataxia type 2 (SCA2), 62 presymptomatics relatives and 80 controls, correlating it with CAG repeat, disease duration and ataxia score were assessed. All the groups showed differences in the amplitude of sensory action potentials in median and sural nerves. Sural amplitude was negatively correlated with disease duration and ataxia score. Differences among patients and controls in the mean latency and conduction velocity of sensory action potentials were found. Abnormal morphology and replicability of SSEPs and BSAEPs were found in patients and presymptomatics. Moreover, consistent increase in latencies of P40 component of SSEPs, III and V peaks and I-III interpeak of BSAEPs was found in patients. A positive correlation was found between latency of III and V waves, I-III and III-V interpeak latencies of BSAEPs and disease duration. CAG repeat and electrophysiological markers assessed were not correlative. Electrophysiological alterations in the SCA2 appeared in presymptomatic stages. These alterations are consistent markers which could be used to evaluate the progression of the disease.

Electrophysiological exploration of visual function in mitochondrial diseases

In a group of 10 children (ranging from 5 months to 15 years old) affected by diseases with mitochondrial dysfunction, 4 suffered from mitochondrial myopathy, 4 from mitochondrial encephalopathy and 2 from Friedreich's ataxia. The clinically detectable visual impairment consisted of 3 grey ocular fundi (the other 7 were normal) associated, in 2 subjects, with a mild nystagmus. Electrophysiological assessment, consisting of ERGs and flash VEPs, was systematically performed. The normal ERGs in all subjects confirmed the normal functioning of retinal electrogenesis. In contrast, the VEPs of 6 out of 10 subjects were modified: in 2 of the 4 subjects with mitochondrial myopathy, the VEPs had a hyperamplitude; in the 2 subjects with Friedreich's ataxia, the implicit time of the principal VEP peaks was increased, together with a hyperamplitude in 1 case; lastly, in 2 of the 4 subjects with mitochondrial encephalopathy, the VEPs were altered. These modifications reflected visual pathway conduction disorders with no clinical expression. Various underlying pathophysiological mechanisms possibly responsible for these modifications are discussed.

Brain-stem auditory evoked potentials and blink reflex in Friedreich's ataxia

The brain-stem involvement in Friedreich's ataxia (FA) was studied by using brain-stem auditory evoked potentials (BAEPs) and the blink reflex. Ten out of 18 patients had abnormal BAEPs, the main abnormality being complete absence of responses and disappearance of wave V. Combined degeneration of the peripheral and central acoustic pathways probably accounts for these findings. The blink reflex was abnormal in 50% of the cases. The outstanding abnormality was bilateral delay of late responses with normal early response, which could be correlated with the known pallor of the descending trigeminal tracts. In contrast with BAEP findings, blink reflex abnormalities did not correlate with either the age of patients or the severity and duration of the disease. These data suggest a difference in susceptibility to degeneration between the auditory system and neuronal system subserving the blink reflex. We conclude that systematic BAEP and blink reflex recording is useful in the electrophysiological evaluation of FA patients.

Utility of short-latency evoked potentials in the classification of progressive, early onset cerebellar ataxias

In recent years, several authors have proposed new classifications of inherited ataxias, some of them being based on systematic clinical studies of large groups of patients. This methodic approach has led to the identification of new types of ataxias and helped the development of molecular biology research in these diseases. Up to now, nerve conduction velocity and evoked potential studies have not been considered in the classification of hereditary ataxias. We have studied the results of short latency evoked potentials in 102 patients affected by a early onset, progressive cerebellar ataxia. Based on the results of this study and a review of the literature on this subject, we will evaluate the utility of nerve conduction velocity and evoked potential recordings in the classification of this group of diseases.

Evoked potential studies in Friedreich's ataxia and progressive early onset cerebellar ataxia

We recorded somatosensory evoked potentials (SEP) in 15 patients affected by Friedreich's ataxia (FA) and in 9 patients with progressive early onset cerebellar ataxia (PEOCA). Brainstem auditory evoked potentials (BAEP) were also recorded in 14 FA patients and in five PEOCA patients. SEP results showed clear differences between groups of FA, evidence of peripheral involvement was seen in all patients, with absence of the N9 potential or a major reduction of its amplitude. In patients in whom central responses could be recorded, conduction velocity was normal or near normal up to the brainstem but was reduced from brainstem to cerebral cortex. Four patients with PEOCA had SEP abnormalities similar to those seen in FA. In the five other patients, the amplitude and latency of N9 were normal but conduction velocity was reduced from brainstem to cerebral cortex. In FA, BAEP were abnormal in all patients with a disease duration of four years or more but were normal in four of the five PEOCA patients. Systematic evoked potential recording is useful in the investigation of hereditary ataxias.