Clinical diagnosis rather than aquaporin-4 immunoglobulin status predicts the cognitive performance in central demyelinating disease

Background: Reports on the aquaporin-4 immunoglobulin G (AQP4-IgG) status for cognitive performance and neuroimaging correlations are limited in neuromyelitis optica (NMO) and multiple sclerosis (MS) literature. Methods: Cognitive results of 19 MS and 15 NMO patients were compared with 47 agematched controls. Apparent diffusion coeffi cient (ADC) values were used to delineate gray matter and white matter damages and correlate with neuropsychological results. Results: Verbal memory test showed signifi cant differences between MS and NMO in the late registration, early and delay recall (p<0.05), while their retention rates were even. In MS, ADC values were signifi cantly elevated in the dorsolateral prefrontal and occipital gray matter which was in contrast with NMO group that showed elevation in the dorsolateral prefrontal gray matter and parieto-occcipital white matter. AQP4-IgG status exerted a limited effect on ADC values and neuropsychological results. Conclusions: Verbal memory test might be helpful in differentiating NMO and MS. ADC values can be used as a surrogate marker for tissue injury in NMO and MS since they were in line with the cognition scores. Anatomical regions with elevated ADC values were different in NMO and MS. Neurology Asia 2012; 17(4) : 331 – 340 Address correspondence to: Dr. Chiung-Chih Chang, Department of Neurology, Kaohsiung Chang Gung Memorial Hospital, #123, Ta-Pei Road, Niaosung, Kaohsiung County 833, Taiwan. Tel: +886-7-731-7123 ext. 3389, Fax: +886-7-731-7123 ext. 3390, E-mail: [email protected] INTRODUCTION Neuromyelitis optica (NMO) and multiple sclerosis (MS) are both demyelinating diseases involving the central nervous system. MS affects the central nervous system more diffusely, whereas NMO affects the optic nerve and spinal cord more selectively, typically sparing the brain. The geographic distributions of MS and NMO are uneven among different populations. In Asia, NMO is more commonly diagnosed and represents 15-56% of previously-diagnosed MS patients in Japan and Taiwan. The introduction of aquaporin-4 immunoglobulin G (AQP4-IgG) in revised NMO criteria has led to increased attention on its clinical impact. AQP4-IgG seropositivity in NMO and MS patients has been reported to be 73% and 9%, respectively. 8 Although AQP4-IgG status has not been fully established as pathognomic for NMO, it enables the differentiation between NMO and MS with a specifi city of 91-100% across different races. 9-11 Identifying these two diseases is of clinical relevance based on the therapeutic perspective and pathogenesis. Although the prevalence of NMO is higher in Asia, the link between AQP4-IgG status and cognitive performance has rarely been reviewed. That the presence of AQP4-IgG was added as an additional feature in the revised criteria and the association with astrocyte membranes in the brain has raised research questions on whether the existence of AQP4-IgG poses any effects on the cognitive performance. Diffusion-weighted magnetic resonance imaging (MRI) has enabled the researchers to obtain a quantitative assessment of the diffusion changes in areas exhibiting signal abnormality in conventional MRI or in areas with normal appearance white matter (WM). By measuring the apparent diffusion coeffi cient (ADC) value, pathological processes that modify tissue integrity could be quantifi ed and analyzed since increase of ADC had been repeatedly reported in disorders with gray matter (GM) pathology and WM diseases. Among demyelinating disorders, Neurology Asia December 2012 332 ADC value also possesses signifi cance in outcome prediction and with pathology correlation. The purpose of this study was to use ADC as a surrogate marker for tissue injury and to evaluate the regional distributions of injury in the GM and WM in patients with MS and NMO. The correlations between ADC values with cognitive performances were performed to ascertain whether changes in ADC refl ected cognitive defi cits in these two groups. NMO patients with positive AQP4-IgG status (AQP-IgG (+)) were further examined as compared with either MS or controls to understand the clinical signifi cance of AQP4IgG status on cognitive performance.