Seasonal prevalence of MS disease activity.
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.
Meier
D S
DS
Center for Neurological Imaging, Brigham & Women's Hospital, 221 Longwood Avenue, RF396, Boston, MA 02115, USA. meier@bwh.harvard.edu
Balashov
K E
KE
Healy
B
B
Weiner
H L
HL
Guttmann
C R G
CR
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
Ann Neurol. 2000 Feb;47(2):276-7
10665507
Neurology. 2002 Sep 10;59(5):688-94
12221158
Ann Neurol. 2001 Mar;49(3):415-6
11261521
J Neurol Sci. 1999 Feb 1;163(1):74-80
10223415
Ann Neurol. 1998 Nov;44(5):824-8
9818941
Ann N Y Acad Sci. 1965 Mar 31;122:457-66
14313505
Neuroimage. 2006 Aug 15;32(2):531-7
16806979
Eur Neurol. 1970;3(5):257-64
5444532
Neurology. 2002 Apr 9;58(7):1077-80
11940696
Neurology. 1983 Jun;33(6):697-701
6682514
J Neuroimmunol. 2007 Aug;188(1-2):181-6
17628701
Stat Med. 2002 Feb 28;21(4):515-31
11836733
AJNR Am J Neuroradiol. 2007 Nov-Dec;28(10):1956-63
17998417
J Neuroimmunol. 2000 May 1;104(2):164-73
10713356
Arch Neurol. 2007 Sep;64(9):1292-8
17846268
Neurology. 2003 Feb 25;60(4):640-6
12601106
J Neuroimmunol. 2001 Aug 30;118(2):286-94
11498263
Arch Neurol. 1999 Aug;56(8):975-80
10448803
Neurol Sci. 2004 Feb;24(6):417-9
14767690
Mult Scler. 2009 May;15(5):627-31
19299440
Neurotherapeutics. 2007 Jul;4(3):485-98
17599713
Lancet. 1985 Jun 8;1(8441):1313-5
2860501
Ann Neurol. 2001 Sep;50(3):422-3
11558803