title: Seasonal prevalence of MS disease activity.
abstract: OBJECTIVE
  This observational cohort study investigated the seasonal prevalence of multiple sclerosis (MS) disease activity (likelihood and intensity), as reflected by new lesions from serial T2-weighted MRI, a sensitive marker of subclinical disease activity.
  
  
  METHODS
  Disease activity was assessed from the appearance of new T2 lesions on 939 separate brain MRI examinations in 44 untreated patients with MS. Likelihood functions for MS disease activity were derived, accounting for the temporal uncertainty of new lesion occurrence, individual levels of disease activity, and uneven examination intervals. Both likelihood and intensity of disease activity were compared with the time of year (season) and regional climate data (temperature, solar radiation, precipitation) and among relapsing and progressive disease phenotypes. Contrast-enhancing lesions and attack counts were also compared for seasonal effects.
  
  
  RESULTS
  Unlike contrast enhancement or attacks, new T2 activity revealed a likelihood 2-3 times higher in March-August than during the rest of the year, and correlated strongly with regional climate data, in particular solar radiation. In addition to the likelihood or prevalence, disease intensity was also elevated during the summer season. The elevated risk season appears to lessen for progressive MS and occur about 2 months earlier.
  
  
  CONCLUSIONS
  This study documents evidence of a strong seasonal pattern in subclinical MS activity based on noncontrast brain MRI. The observed seasonality in MS disease activity has implications for trial design and therapy assessment. The observed activity pattern is suggestive of a modulating role of seasonally changing environmental factors or season-dependent metabolic activity.
authors.affiliation: Center for Neurological Imaging, Brigham & Women's Hospital, 221 Longwood Avenue, RF396, Boston, MA 02115, USA. meier@bwh.harvard.edu
authors.forename: D S
authors.initials: DS
authors.lastname: Meier
authors.forename: K E
authors.initials: KE
authors.lastname: Balashov
authors.forename: B
authors.initials: B
authors.lastname: Healy
authors.forename: H L
authors.initials: HL
authors.lastname: Weiner
authors.forename: C R G
authors.initials: CR
authors.lastname: Guttmann
mesh_terms: D000328:Adult; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000639:trends; D008297:Male; D008875:Middle Aged; D020528:Multiple Sclerosis, Chronic Progressive / Q000453:epidemiology* / Q000473:pathology*; D015995:Prevalence; D012189:Retrospective Studies; D012307:Risk Factors; D012621:Seasons
references.citation: Ann Neurol. 2000 Feb;47(2):276-7
references.pmid: 10665507
references.citation: Neurology. 2002 Sep 10;59(5):688-94
references.pmid: 12221158
references.citation: Ann Neurol. 2001 Mar;49(3):415-6
references.pmid: 11261521
references.citation: J Neurol Sci. 1999 Feb 1;163(1):74-80
references.pmid: 10223415
references.citation: Ann Neurol. 1998 Nov;44(5):824-8
references.pmid: 9818941
references.citation: Ann N Y Acad Sci. 1965 Mar 31;122:457-66
references.pmid: 14313505
references.citation: Neuroimage. 2006 Aug 15;32(2):531-7
references.pmid: 16806979
references.citation: Eur Neurol. 1970;3(5):257-64
references.pmid: 5444532
references.citation: Neurology. 2002 Apr 9;58(7):1077-80
references.pmid: 11940696
references.citation: Neurology. 1983 Jun;33(6):697-701
references.pmid: 6682514
references.citation: J Neuroimmunol. 2007 Aug;188(1-2):181-6
references.pmid: 17628701
references.citation: Stat Med. 2002 Feb 28;21(4):515-31
references.pmid: 11836733
references.citation: AJNR Am J Neuroradiol. 2007 Nov-Dec;28(10):1956-63
references.pmid: 17998417
references.citation: J Neuroimmunol. 2000 May 1;104(2):164-73
references.pmid: 10713356
references.citation: Arch Neurol. 2007 Sep;64(9):1292-8
references.pmid: 17846268
references.citation: Neurology. 2003 Feb 25;60(4):640-6
references.pmid: 12601106
references.citation: J Neuroimmunol. 2001 Aug 30;118(2):286-94
references.pmid: 11498263
references.citation: Arch Neurol. 1999 Aug;56(8):975-80
references.pmid: 10448803
references.citation: Neurol Sci. 2004 Feb;24(6):417-9
references.pmid: 14767690
references.citation: Mult Scler. 2009 May;15(5):627-31
references.pmid: 19299440
references.citation: Neurotherapeutics. 2007 Jul;4(3):485-98
references.pmid: 17599713
references.citation: Lancet. 1985 Jun 8;1(8441):1313-5
references.pmid: 2860501
references.citation: Ann Neurol. 2001 Sep;50(3):422-3
references.pmid: 11558803