title: Warmer outdoor temperature is associated with worse cognitive status in multiple sclerosis.
abstract: OBJECTIVE
  Patients with multiple sclerosis (MS) have more clinical exacerbations and T2 lesion activity during warmer weather. The current study is the first to investigate whether outdoor temperature is related to cognitive status across patients with MS (cross-sectional analysis), and whether cognitive status fluctuates with changes in outdoor temperature within patients with MS (longitudinal analysis).
  
  
  METHODS
  For the cross-sectional analysis, 40 patients with MS and 40 healthy control (HC) subjects were recruited throughout the calendar year. Cognitive status (processing speed, memory) and outdoor temperature were recorded for the day of testing. We calculated partial correlations between cognitive status and temperature for patients with MS and HCs, controlling for demographic and disease variables. For the longitudinal analysis, cognitive status and outdoor temperature were recorded at baseline and 6-month follow-up in a separate sample of 45 patients with MS. We calculated the partial correlation between temperature and cognitive status at follow-up, controlling for baseline temperature and cognitive status (i.e., whether temperature changes are related to cognitive changes within patients with MS).
  
  
  RESULTS
  Cross-sectionally, warmer temperature was related to worse cognitive status in patients with MS (r(p) = -0.45, p = 0.006), not in HCs (r(p) = 0.00, p = 0.984). Longitudinally, increased outdoor temperature from baseline to follow-up was related to a decline in cognitive status within patients with MS (r(p) = -0.39, p = 0.010).
  
  
  CONCLUSIONS
  Cognitive status in patients with MS is worse on warmer days, consistent with a previously established link between heat and lesion activity. Our findings have implications for clinical trial planning, treatment, and lifestyle decisions. We discuss cognitive status as a potential marker of quiescent exacerbations.
authors.affiliation: Kessler Foundation Research Center, West Orange, NJ, USA. vleavitt@kesslerfoundation.org
authors.forename: Victoria M
authors.initials: VM
authors.lastname: Leavitt
authors.forename: James F
authors.initials: JF
authors.lastname: Sumowski
authors.forename: Nancy
authors.initials: N
authors.lastname: Chiaravalloti
authors.forename: John
authors.initials: J
authors.lastname: Deluca
mesh_terms: D000328:Adult; D003072:Cognition Disorders / Q000453:epidemiology* / Q000523:psychology*; D003430:Cross-Sectional Studies; D004777:Environment; D005260:Female; D005500:Follow-Up Studies; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000453:epidemiology* / Q000523:psychology*