title: Geographic variation and environmental risk factors for the incidence of initial kidney stones in patients with spinal cord injury.
abstract: OBJECTIVE
  Although geographic variability in cases of kidney stones, primarily calcium stones, is reported in the general population, little is known about geographic variability in subjects with spinal cord injury, in whom struvite stones predominate. We examined regional variation in the incidence rate of initial kidney stones and clarified the contributing factors in a spinal cord injury cohort.
  
  
  METHODS
  We used data from the national spinal cord injury database between 1986 and 1999 on 7,784 participants from 21 spinal cord injury centers with 24,492 person-years of followup accumulated and 286 incident stone cases. A multilevel Poisson model was constructed to evaluate the ecological effects of latitude, air temperature, water hardness and sunlight index on stone formation while controlling for individual factors, including participant age, race, gender, severity of injury and bladder management.
  
  
  RESULTS
  The incidence rate was significantly greater in the southeast and tended to increase with decreasing latitude, similar to the geographic association with kidney stones in the general population. This finding was not explained by differences in individual risk factors. Decreasing water hardness had the strongest effect on stones during year 1 after injury (relative risk 0.6, p <0. 001), whereas average annual temperature had the strongest association with stones after year 1 (relative risk 1.1 per 1C increase, p = 0.03). The sunlight index had no association.
  
  
  CONCLUSIONS
  Our study implies that the increased stone risk in spinal cord injured subjects is potentially preventable by modifying environmental exposure. Etiological factors may be similar to those for kidney stones in the general population.
authors.affiliation: Departments of Physical Medicine and Rehabilitation, and Epidemiology, School of Public Health, University of Alabama at Birmingham, Birmingham, Alabama, USA.
authors.forename: Y Y
authors.initials: YY
authors.lastname: Chen
authors.forename: J M
authors.initials: JM
authors.lastname: Roseman
authors.forename: M J
authors.initials: MJ
authors.lastname: Devivo
authors.forename: C T
authors.initials: CT
authors.lastname: Huang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004777:Environment; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D007669:Kidney Calculi / Q000453:epidemiology* / Q000209:etiology; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D013119:Spinal Cord Injuries / Q000150:complications*; D014481:United States / Q000453:epidemiology