Chromatic pattern-reversal electroretinograms (ChPERGs) are spared in multiple system atrophy compared with Parkinson's disease

Abstract

Idiopathic Parkinson's disease (IPD) patients have abnormal visual evoked potentials (VEPs) and pattern electroretinograms (PERGs), attributed to dopaminergic transmission deficiency in visual pathway, probably the retina. VEP abnormalities are not reported in multiple system atrophy (MSA). The aim of this study was to investigate and compare chromatic (Ch) red-green (R-G) and blue-yellow (B-Y), and luminance yellow-black (Y-Bk) PERGs in patients with MSA and IPD. We investigated 6 MSA patients (mean age: 62+/-7.4 years) not undergoing any pharmacological treatment, as well as 12 early IPD patients (mean age: 60.1+/-8.3 years) and 12 age-matched normal observers. ChPERGs were recorded monocularly in response to full-field equiluminant R-G, B-Y and Y-Bk horizontal gratings. In MSA only responses to R-G stimuli showed minimal insignificant changes (slight but not significant amplitude reduction without any significant latency delay); no significant abnormality was detected for B-Y and luminance Y-Bk stimuli. By contrast, in IPD all responses were reduced in amplitude and delayed in latency, above all for B-Y stimuli. Present data indicate that both chromatic and achromatic PERGs are virtually unaffected in MSA, whereas in early IPD they are clearly impaired, suggesting different pathogenic retinal mechanisms and a useful simple tool for distinguishing MSA from IPD.

Fig. 1

Examples of transient ChPERGs in a MSA patient (Z.E., m, 59 years; top traces), an IPD patient (C.G., m, 64 years; middle traces) and a control observer (D.R.C., f, 51 years; bottom traces) for all the three stimuli reported in a cascade way. Two traces are superimposed for each stimuli condition to ensure reliability. P1 and N1 components are labelled for each PERG waveform and type of stimulus. Note the evident amplitude loss and tendency to latency shift for B-Y gratings in the IPD cases

Fig. 2

Mean (±Std. Err. ChPERGs) amplitude (mV) on the left and latency (ms) on the right histograms in controls (white columns), IPD (grey columns) and MSA (black columns) patients. Note that PERGs are substantially spared in MSA patients, whereas they are reduced and delayed in early IPD patients, especially for B-Y stimuli (**p<0.01)