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C. S. Barnes, N. Newman, G. Wilmot, J. Yan; Negative ERGs in Cerebellar Degeneration. Invest. Ophthalmol. Vis. Sci. 2007;48(13):932.
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Recent reports have documented "negative ERGs" (maximal-flash electroretinogram response with the b-wave selectively reduced) in a small number of patients with cerebellar degeneration,1-3 a heterogeneous group of diseases causing ataxia (loss of coordination) as the main symptom. Five cases were hereditary (2 with spinocerebellar ataxia 1 (SCA-1) gene mutations) whereas 2 had sporadic disease without clearly established diagnoses. Here we report a negative ERG in another sporadic cerebellar degeneration patient whose phenotype differs markedly from those reported to date.
The patient was a 65-year-old man with a 5 year history of gait unsteadiness and orthostatic hypotension requiring fludrocortisone treatment. He had bladder and erectile dysfunction but no signs of cognitive, pyramidal, or extrapyramidal involvement. Gait ataxia was prominent and ataxia was present in all 4 limbs. Family history was negative for neurological or retinal disorders. He had a comprehensive eye exam as well as visual fields and autofluorescence. Full-field ERG responses were recorded using DTL electrodes.
The patient’s visual acuity was 20/30 OD and 20/40 OS, but he reportedly has never had 20/20 acuity. He scored < 2/14 on Ishihara plates. External exam was significant for end-gaze nystagmus. Fundus exam showed optic nerve atrophy, but otherwise was within normal limits. Autofluorescence showed a normal RPE layer. His visual fields had enlarged blind spots. The patient’s photopic flash and 30-Hz ERG responses were normal in amplitude and implicit time. His rod b-waves were reduced and delayed, but the maximal-flash a-waves were normal. Maximal-flash b-wave amplitudes were ≤ his a-waves. Blood tests were negative for Leber’s hereditary optic neuropathy and dominant optic atrophy. Tests for trinucleotide repeat expansions in SCA genes 1-3, 6-8 and 17 are ongoing.
This is only the third reported case of sporadic ataxia associated with a negative ERG. The patient’s prominent autonomic dysfunction differs significantly from the previous cases, and in fact he meets the clinical criteria for probable multiple system atrophy (MSA).4 This introduces another possible diagnosis to consider in cases of a negative ERG associated with ataxia. Further investigation of ERGs in patients with cerebellar degeneration may help to define the significance of negative ERGs in this patient population.References:1. Kimura et al. Doc Ophthalmol 2004;108:241-2472. Hagan et al. IOVS 2005;46: Abstract 45583. Ochiai et al. IOVS 2006;47: Abstract 58064. Gilman et al. J Neurol Sci 1999; 163:94-98
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