Latitudinal variation in incidence and type of first central nervous system demyelinating events

• Published in: Multiple sclerosis 2010-04, Vol.16 (4), p.398-405
• Main Authors: Taylor, Bruce V, Lucas, Robyn M, Dear, Keith, Kilpatrick, Trevor J, Pender, Michael P, van der Mei, Ingrid AF, Chapman, Caron, Coulthard, Alan, Dwyer, Terence, McMichael, Anthony J, Valery, Patricia C, Williams, David, Ponsonby, Anne-Louise
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Australia - epidemiology; Biological and medical sciences; Case-Control Studies; Central Nervous System Diseases - epidemiology; Central Nervous System Diseases - etiology; Cerebellar Diseases - epidemiology; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Demyelinating Diseases - epidemiology; Demyelinating Diseases - etiology; Female; Human viral diseases; Humans; Incidence; Infectious diseases; Male; Medical sciences; Middle Aged; Multiple Sclerosis, Chronic Progressive - epidemiology; Multiple Sclerosis, Chronic Progressive - etiology; Neurology; Optic Neuritis - epidemiology; Residence Characteristics; Risk Factors; Sex Distribution; Sex Factors; Spinal Cord Diseases - epidemiology; Time Factors; Viral diseases; Viral diseases of the lymphoid tissue and the blood. Aids; Young Adult
• ISSN: 1352-4585; 1477-0970
• DOI: 10.1177/1352458509359724

Increasing prevalence and variable geographic patterns of occurrence of multiple sclerosis suggest an environmental role in causation. There are few descriptive, population-level, data on whether such variability applies to first demyelinating events (FDEs). We recruited 216 adults (18—59 years), with a FDE between 1 November 2003 and 31 December 2006 in a multi-center incident case-control study in four locations on the south-eastern and eastern seaboard of Australia, spanning latitudes 27° south to 43° south. Population denominators were obtained from the Australian Bureau of Statistics censuses of 2001 and 2006. Age and sex adjusted FDE incidence rates increased by 9.55% (95% confidence interval (CI) 7.37—11.78, p < 0.001) per higher degree of latitude. The incidence rate gradient per higher degree of latitude varied by gender (male: 14.69% (95% CI 9.68—19.94, p < 0.001); female 8.13% (95% CI 5.69—10.62, p < 0.001)); and also by the presenting FDE type: optic neuritis 11.39% (95% CI 7.15—15.80, p < 0.001); brainstem/cerebellar syndrome 9.47% (95% CI 5.18—13.93, p < 0.001); and spinal cord syndrome 5.36% (95% CI 1.78—9.06, p = 0.003). Differences in incidence rate gradients were statistically significant between males and females (p = 0.02) and between optic neuritis and spinal cord syndrome (p = 0.04). The male to female ratio varied from 1 : 6.7 at 27° south to 1 : 2.5 at 43° south. The study establishes a positive latitudinal gradient of FDE incidence in Australia. The latitude-related factor(s) influences FDE incidence variably according to subtype and gender, with the strongest influence on optic neuritis presentations and for males. These descriptive case analyses show intriguing patterns that could be important for understanding the etiology of multiple sclerosis.