A negative electroretinogram (ERG) in a case of probable multiple system atrophy (MSA)

Abstract

Recent articles have described negative ERGs in a small number of patients with cerebellar degeneration. Five of the previously reported seven cases were hereditary (2/5 had spinocerebellar ataxia-1 (SCA-1) gene mutations) and the other two were sporadic. We report a negative ERG in a case of cerebellar degeneration that differs significantly from earlier cases. The 65-year-old man had a 5-year history of ataxia, unsteady gait, orthostatic hypotension, and bladder and erectile dysfunction, with no family history of neurological or retinal disease. Visual acuity was 20/30 OD, 20/40 OS, but reportedly was never 20/20. His fundus exam showed optic nerve pallor, but otherwise was normal. Visual fields had enlarged blind spots but no central scotomas. Autofluorescence was normal. Photopic flash and 30-Hz ERG responses were normal. Rod b-waves were reduced and delayed. Standard flash a-waves were normal, but the b-waves were smaller than the a-waves. Blood tests were negative for Leber's hereditary optic neuropathy, dominant optic atrophy, and for expansions in SCA genes including SCA-1. This is only the third reported case of sporadic ataxia with a negative ERG. The patient's prominent autonomic dysfunction differs from the previous cases, and meets the clinical criteria for probable multiple system atrophy (MSA). This introduces another possible diagnosis in cases of negative ERGs with ataxia, and suggests that the visual system may be affected in MSA.

Retinal Nerve Fibre Layer and Macular Thinning in Spinocerebellar Ataxia and Cerebellar Multisystem Atrophy

“…28–30 This is supported by occasional reports of retinal or optic nerve involvement in these disorders as well as in MSA-C. 8,13,15,16 In this study we investigated the relationship of the thickness of the retinal nerve fibre layer and macula by OCT in patients with genetically confirmed SCA and MSA-C. The aim of our study was to test the hypothesis that subclinical neuronal or axonal loss in the retina may occur in the degenerative ataxias and be detected as thinning of the RNFL or macula.…”

“…8 Visual evoked potentials, sensitive for determining subclinical involvement of the visual pathways, are abnormal in the majority of SCA1 patients. 8,9 Optic atrophy has been described in SCA2 and SCA3, and in MSA-C. 10–13 Rarely, SCA2 is also associated with retinitis pigmentosa, most notably in the infantile form with extremely expanded CAG repeats. 14,15 Pigmentary retinopathy has been reported in a patient homozygous for a pathological repeat expansion in the SCA6 gene.…”

Visual signs and symptoms of multiple system atrophy

“…There have been few studies of visual field defects in patients with any parkinsonian syndrome, which may be a consequence of the difficulties of testing patients with a movement disorder. A case of multiple system atrophy has been reported with enlarged blind spots but with no central scotoma . Some patients with neurodegenerative disease, in whom impairment in VA has been demonstrated, also exhibit impairment of stereopsis as measured by random‐dot stereograms but there is currently little information available for the parkinsonian syndromes.…”

Optical Coherence Tomography in Parkinsonian Syndromes

“…Also, the function of retinal ganglion cells seems to be altered as shown by pattern electroretinograms (ERG) [8], [9], [10], [11]. In a patient with MSA, optic disc pallor and negative ERGs were observed [12]. Visual event related potentials using a visual oddball paradigm were reported to be abnormal in all four diseases [13].…”