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Stuart G Coupland, Lulu L.C.D. Bursztyn, Jillian Belrose, J. Alexander Fraser, Alain A Proulx; Role of α-enolase Autoantibodies related to Rod-bipolar cell function in Non-paraneoplastic Autoimmune Retinopathy. Invest. Ophthalmol. Vis. Sci. 2014;55(13):331.
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Autoimmune retinopathies are rare disorders whose visual prognosis is typically poor. Here we report a case of α-enolase mediated npAIR with marked ERG dysfunction which demonstrated dramatic clinical improvement with a short course of oral corticosteroids, and concomitant disappearance of α-enolase autoantibodies and with unique electrophysiological presentation that points to the role of α-enolase autoantibodies in modulating rod on-bipolar cell function, distinct from cone on-bipolar cell function.
ERGs were recorded to ISCEV standards for rod, combined rod-cone, cone and 30 Hz flicker conditions. In addition, ERG responses were recorded to sawtooth flicker of luminance of 150 cd/m2 flickering at 8 Hz. with 100% contrast using Espion e3 (Diagnosys LLC) system with DTL microconductive fiber electrodes. Both rapid-ON and rapid-OFF components were examined for reduced b- to d-wave amplitude ratio indicative of ON pathway dysfunction. Anti-retinal autoantibody testing by Western blot analysis was also performed in the same time period as ERG. After short course of oral corticosteroids patient showed marked improvement in visual function and was seen 12 months later for repeat testing.
Initially, ERG was abnormal to scotopic flash, photopic flash and 30Hz flicker stimulation with a definite negative ERG appearance noted. On-off ERG using 8 Hz sawtooth flicker demonstrated complete loss of the cone on-response with preservation of a normal off-response, suggesting selective loss of cone depolarizing bipolar cell (DBC) function in the inner retina. Anti-retinal autoantibody testing by Western blot was positive for 46-kDa (α-enolase), 50-kDa and 62-kDa proteins. At one year follow-up ERG showed full recovery of rod function with no improvement in photopic cone ERG. On-Off ERG showed only slight evidence of a cone on-response confirming selective loss of cone DBC function in the inner retina. Repeat anti-retinal antibody testing demonstrated the previously identified 46kDa α-enolase reactive band was not observed.
Since rod ERG b-wave amplitude is entirely dependent on the rod DBC, these findings support a pathological role for α-enolase autoantibodies related to rod-bipolar cell function. Identification of other cases which exhibit such improvements and the associated autoantibody activity may enhance our understanding of disease pathogenesis.
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