Characterisation of the spectrum of demyelinating disease in Western Australia

Background: The diversity of multiple sclerosis (MS) and the nosology of the conventional form of MS (CMS), optic-spinal MS (OSMS) and neuromyelitis optica (NMO) have been subject to controversy. Aims: The purpose of this study was to investigate whether the current Asian optic-spinal multiple sclerosis (OSMS) criteria could also apply in Western countries, and whether or not cerebrospinal fluid (CSF) and imaging features in the Western Australian patient population of demyelinating disease was similar to that found in Asia. Methods: This study retrospectively reviewed 915 individual case notes with central nervous system demyelinating disease seen by two neurologists in Western Australia (WA). 842 cases had sufficient data to be included in the analysis. The patient population was predominantly Caucasian, representing approximately two-thirds of MS cases in WA. The mean duration of follow-up for the whole studied cohort was 12.5 years, with 136 patients (16.2%) being followed-up for more than 20 years. Results: The study confirmed the relatively low frequency of OSMS as a proportion of total demyelinating disease occurring in western countries, with 31 OSMS (3.7%) cases in contrast to 703 CMS cases (83.5%). It is likely, however, that our retrospective classification significantly underestimated the proportion of OSMS cases when compared with prospectively classified Asian cohorts. There were 11 OSMS cases that could also be classified as NMO according to published diagnostic criteria. The remainder of the spectrum comprised clinically isolated syndromes such as 50 acute myelitis (AM, 5.9%), 42 optic neuritis (ON, 5%) and 16 "atypical'' cases such as tumefactive MS and acute disseminated encephalomyelitis (1.9%). The clinical characteristics of OSMS in our study were compatible with so-called Asian MS in many respects: oligoclonal bands (OCBs) were less frequent in OSMS (29.4%) than in CMS (66.4%, p= 0.003); visual evoked potentials and spinal MRI abnormalities were more prevalent in OSMS (85% and 92.6%) than in CMS (71.4% and 85%); as were long spinal cord lesions in OSMS (22.2%) versus CMS (3.4%, p, 0.001). Brain abnormalities were seen in 48.4% of OSMS patients and 96.2% of CMS patients (p= 0.001). OCBs were identified in 7% of acute myelitis, 14.3% of optic neuritis and 73.4% of primary progressive MS patients. Conclusions: This cross-sectional study presents the full spectrum of demyelinating disease in WA, which has a stable population representing 10% of the total Australian population and suggests that the current classifications of MS, OSMS or NMO, ON and AM share many clinical and laboratory features, such as female predominance, age at onset, duration of disease and CSF investigations (including OCBs and MRI). Moreover, characteristics of the WA population were similar to those reported in Asian patients.