Editorial
Risk factors for mortality in spinal cord injury Anthony F. DiMarco 1 , Neal V. Dawson 2 1 2
Department of Physical Medicine & Rehabilitation, The Case Western Reserve University, Cleveland, OH, USA, Department of Medicine, The Case Western Reserve University, Cleveland, OH, USA
It is well known that survival rates in subjects with spinal cord injury (SCI) are significantly lower than in the ablebodied population.1 Several studies have been performed to identify risk factors which impact life quality and survival time.2–7 These epidemiologic studies are important to determine specific survival estimates within subgroups, assess the societal economic burden, provide for proper allocation of health care resources, and perhaps most important, identify more targeted therapeutic interventions to be evaluated.8 Over the past several decades, the mortality rate during the first 2 years after SCI has declined dramatically, by ∼40% due to improved medical care in the field of critical care. Unfortunately, improvements in mortality beyond this period have been very small and not significant.6 This statistic highlights the importance of identifying factors affecting survival in the chronic SCI population and means by which life expectancy can be improved. While life expectancy is important, it should be remembered that it is equally important to identify factors which address and improve life quality. Excluding individuals who are ventilator dependent, a number of predictors of mortality in the SCI population beyond the initial 2-year period have been identified. Using Model Systems data with a database of more than 30 000 individuals, Strauss et al. 6 found a substantial difference in survival based upon level and completeness of injury. In general, mortality risk increases with increasing degree of neurologic impairment. Among those with cervical injuries, mortality was highest for high cervical injuries; there was a gradual reduction in mortality with progressively lower levels of injury. Mortality was also substantially higher for those with complete (ASIA A) injuries compared for those with incomplete (ASIA B or C) injuries. For paraplegia, Correspondence to: Anthony F. DiMarco, Department of Physical Medicine & Rehabilitation, The Case Western Reserve University, MetroHealth Campus, 2500 MetroHealth Drive, R551, Cleveland, OH 44109, USA. Email: [email protected]
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© The Academy of Spinal Cord Injury Professionals, Inc. 2014 DOI 10.1179/2045772314Y.0000000208
there was no increase in mortality. Age at time of injury is important as mortality increases with higher age.3,6 Male sex and violent etiology are also risk factors.3,5,6,8 While urinary tract complications and renal failure were the leading causes of death in the 1950s, more recent studies have demonstrated a marked shift to pneumonia and other respiratory complications as the most common.1,3,9 The studies of Weaver et al. 10 who evaluated the outcomes of outpatient visits for acute respiratory illness highlight the significant impact of respiratory illnesses. In their assessment of over 8700 out-patient visits for acute respiratory illness, ∼31% required hospitalization and 60-day mortality was 7.9% for pneumonia and 2.9% overall. It is important to note, however, that heart disease and cancer have been increasing steadily as common causes of death, as well.2,3,8,11 In this issue of the Journal, Danilack et al. 12 report on the associations between chest illness and mortality in chronic SCI. Their primary conclusion is that the occurrence of chest illness in the preceding 3 years was not an independent risk factor for mortality and was not associated with level and completeness of SCI, but was associated with current smoking, history of chronic obstructive pulmonary disease, and cardiac disease. Prior to evaluating the significance to the results of this study, it is important to note that the occurrence of chest illness in this study was determined by response to a questionnaire that queried whether these subjects experienced a chest illness in the prior 3 years. When recall of life events has been systematically studied,13,14 the accuracy beyond 6 months has been shown to be limited, raising questions concerning the degree of validity of this retrospective approach. Recall ability may also vary across subjects with different levels of impairment. Moreover, while the investigators state that this method was validated in a prior study, median contact was more recent (1.7 years), verification was attempted
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DiMarco and Dawson
only for hospitalizations (41/247 instances of chest illness), and confirmed in only 30/41 cases in that study.15 Another concern is whether the study was sufficiently powered to detect a potential relationship between chest illness and mortality. In a prior study11 in which these investigators assessed the relationship between comorbid medical conditions and mortality in the same patient cohort, a relationship between neurological level and completeness was not detectable. However, with further follow-up in a somewhat larger cohort and larger number of deaths ( presented in the current study), this relationship became evident. Therefore, the possibility of a relationship between chest illness and mortality should not be discounted entirely among patients who are at least 4 years out from SCI. Lastly, an important limitation is the lack of availability of the causes of death. Conceivably, those subjects with a history of prior chest illness may have been more likely to succumb to a respiratory related cause of death. Additional clarity about the effect of various causes of mortality across time may be developed by evaluating a large longitudinal cohort of SCI patients using analytic techniques that adequately account for differential mortality pressure. This approach can help us better understand competing risks for mortality across the life experience of the cohort. For example, higher risk for respiratory illness-related mortality may occur early in the course of SCI and increasing risk of cardiovascular deaths may become evident as the cohort ages. In addition, the use of data reduction techniques that produce relatively independent combinations of variables or predictive dimensions may avoid the falsely negative results sometimes produced by statistical approaches that seek to identify the independent effect of individual variables that are statistically and mechanistically correlated. Despite its limitations, the study of Danilack et al. 12 elucidates some potentially modifiable predictors of mortality, which have been suggested by others.6,7,11,16 Most notably, there was a strong relationship between cigarette smoking and the disease states occurring as a consequence, including obstructive airway diseases and cardiac disease, and mortality. A reduction in lung function was also strongly associated with mortality, another consequence of smoking. As with the able bodied,
Risk factors for mortality in SCI
cigarette smoking is an important contributor to mortality in the SCI population. Therefore, as suggested by previous investigators,3,6,7,11 more attention should be directed to smoking cessation to achieve a reduction in the rate of respiratory complications, vascular disease, and cancer among patients with chronic SCI, an endeavor which may become even more important as this high-risk population ages.
References 1 DeVivo MJ, Stover SL, Black KJ. Prognostic factors for 12-year survival after spinal cord injury. Arch Phys Med Rehabil 1992; 73(2):156–62. 2 Yeo JD, Walsh J, Rutkowski S, Soden R, Craven M, Middleton J. Mortality following spinal cord injury. Spinal Cord 1998;36(5): 329–36. 3 Frankel HL, Coll JR, Charlifue SW, Whiteneck GG, Gardner BP, Jamous MA, et al. Long-term survival in spinal cord injury: a fifty year investigation. Spinal Cord 1998;36(4):266–74. 4 Middleton JW, Dayton A, Walsh J, Rutkowski SB, Leong G, Duong S. Life expectancy after spinal cord injury: a 50-year study. Spinal Cord 2012;50(11):803–11. 5 DeVivo MJ, Krause JS, Lammertse DP. Recent trends in mortality and causes of death among persons with spinal cord injury. Arch Phys Med Rehabil 1999;80(11):1411–9. 6 Strauss DJ, DeVivo MJ, Paculdo DR, Shavelle RM. Trends in life expectancy after spinal cord injury. Arch Phys Med Rehabil 2006; 87(8):1079–85. 7 Krause JS, Saunders LL. Risk of mortality and life expectancy after spinal cord injury: the role of health behaviors and participation. Top Spinal Cord Inj Rehabil 2010;16(2):53–60. 8 van den Berg ME, Castellote JM, de Pedro-Cuesta J, MahilloFernandez I. Survival after spinal cord injury: a systematic review. J Neurotrauma 2010;27(8):1517–28. 9 Whiteneck GG, Charlifue SW, Frankel HL, Fraser MH, Gardner BP, Gerhart KA, et al. Mortality, morbidity, and psychosocial outcomes of persons spinal cord injured more than 20 years ago. Paraplegia 1992;30(9):617–30. 10 Weaver FM, Smith B, Evans CT, Kurichi JE, Patel N, Kapur VK, et al. Outcomes of outpatient visits for acute respiratory illness in veterans with spinal cord injuries and disorders. Am J Phys Med Rehabil 2006;85(9):718–26. 11 Garshick E, Kelley A, Cohen SA, Garrison A, Tun CG, Gagnon D, et al. A prospective assessment of mortality in chronic spinal cord injury. Spinal Cord 2005;43(7):408–16. 12 Danilack VA, Stolzmann KL, Gagnon DR, Brown R, Tun CG, Morse LR, et al. Associations with chest illness and mortality in chronic spinal cord injury. J Spinal Cord Med 2014;37(6):662–9. 13 Litwin MS, McGuigan KA. Accuracy of recall in health-related quality-of-life assessment among men treated for prostate cancer. J Clin Oncol 1999;17(9):2882–8. 14 Jenkins CD, Hurst MW, Rose RM. Life changes: do people really remember? Arch Gen Psychiatry 1979;36(4):379–84. 15 Stolzmann KL, Gagnon DR, Brown R, Tun CG, Garshick E. Risk factors for chest illness in chronic spinal cord injury: a prospective study. Am J Phys Med Rehabil 2010;89(7):576–83. 16 Weaver FM, Smith B, LaVela SL, Evans CT, Ullrich P, Miskevics S, et al. Smoking behavior and delivery of evidence-based care for veterans with spinal cord injuries and disorders. J Spinal Cord Med 2011;34(1):35–45.
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Risk factors for mortality in spinal cord injury Anthony F. DiMarco 1 , Neal V. Dawson 2 1 2
Department of Physical Medicine & Rehabilitation, The Case Western Reserve University, Cleveland, OH, USA, Department of Medicine, The Case Western Reserve University, Cleveland, OH, USA
It is well known that survival rates in subjects with spinal cord injury (SCI) are significantly lower than in the ablebodied population.1 Several studies have been performed to identify risk factors which impact life quality and survival time.2–7 These epidemiologic studies are important to determine specific survival estimates within subgroups, assess the societal economic burden, provide for proper allocation of health care resources, and perhaps most important, identify more targeted therapeutic interventions to be evaluated.8 Over the past several decades, the mortality rate during the first 2 years after SCI has declined dramatically, by ∼40% due to improved medical care in the field of critical care. Unfortunately, improvements in mortality beyond this period have been very small and not significant.6 This statistic highlights the importance of identifying factors affecting survival in the chronic SCI population and means by which life expectancy can be improved. While life expectancy is important, it should be remembered that it is equally important to identify factors which address and improve life quality. Excluding individuals who are ventilator dependent, a number of predictors of mortality in the SCI population beyond the initial 2-year period have been identified. Using Model Systems data with a database of more than 30 000 individuals, Strauss et al. 6 found a substantial difference in survival based upon level and completeness of injury. In general, mortality risk increases with increasing degree of neurologic impairment. Among those with cervical injuries, mortality was highest for high cervical injuries; there was a gradual reduction in mortality with progressively lower levels of injury. Mortality was also substantially higher for those with complete (ASIA A) injuries compared for those with incomplete (ASIA B or C) injuries. For paraplegia, Correspondence to: Anthony F. DiMarco, Department of Physical Medicine & Rehabilitation, The Case Western Reserve University, MetroHealth Campus, 2500 MetroHealth Drive, R551, Cleveland, OH 44109, USA. Email: [email protected]
670
© The Academy of Spinal Cord Injury Professionals, Inc. 2014 DOI 10.1179/2045772314Y.0000000208
there was no increase in mortality. Age at time of injury is important as mortality increases with higher age.3,6 Male sex and violent etiology are also risk factors.3,5,6,8 While urinary tract complications and renal failure were the leading causes of death in the 1950s, more recent studies have demonstrated a marked shift to pneumonia and other respiratory complications as the most common.1,3,9 The studies of Weaver et al. 10 who evaluated the outcomes of outpatient visits for acute respiratory illness highlight the significant impact of respiratory illnesses. In their assessment of over 8700 out-patient visits for acute respiratory illness, ∼31% required hospitalization and 60-day mortality was 7.9% for pneumonia and 2.9% overall. It is important to note, however, that heart disease and cancer have been increasing steadily as common causes of death, as well.2,3,8,11 In this issue of the Journal, Danilack et al. 12 report on the associations between chest illness and mortality in chronic SCI. Their primary conclusion is that the occurrence of chest illness in the preceding 3 years was not an independent risk factor for mortality and was not associated with level and completeness of SCI, but was associated with current smoking, history of chronic obstructive pulmonary disease, and cardiac disease. Prior to evaluating the significance to the results of this study, it is important to note that the occurrence of chest illness in this study was determined by response to a questionnaire that queried whether these subjects experienced a chest illness in the prior 3 years. When recall of life events has been systematically studied,13,14 the accuracy beyond 6 months has been shown to be limited, raising questions concerning the degree of validity of this retrospective approach. Recall ability may also vary across subjects with different levels of impairment. Moreover, while the investigators state that this method was validated in a prior study, median contact was more recent (1.7 years), verification was attempted
The Journal of Spinal Cord Medicine
2014
VOL.
37
NO.
6
DiMarco and Dawson
only for hospitalizations (41/247 instances of chest illness), and confirmed in only 30/41 cases in that study.15 Another concern is whether the study was sufficiently powered to detect a potential relationship between chest illness and mortality. In a prior study11 in which these investigators assessed the relationship between comorbid medical conditions and mortality in the same patient cohort, a relationship between neurological level and completeness was not detectable. However, with further follow-up in a somewhat larger cohort and larger number of deaths ( presented in the current study), this relationship became evident. Therefore, the possibility of a relationship between chest illness and mortality should not be discounted entirely among patients who are at least 4 years out from SCI. Lastly, an important limitation is the lack of availability of the causes of death. Conceivably, those subjects with a history of prior chest illness may have been more likely to succumb to a respiratory related cause of death. Additional clarity about the effect of various causes of mortality across time may be developed by evaluating a large longitudinal cohort of SCI patients using analytic techniques that adequately account for differential mortality pressure. This approach can help us better understand competing risks for mortality across the life experience of the cohort. For example, higher risk for respiratory illness-related mortality may occur early in the course of SCI and increasing risk of cardiovascular deaths may become evident as the cohort ages. In addition, the use of data reduction techniques that produce relatively independent combinations of variables or predictive dimensions may avoid the falsely negative results sometimes produced by statistical approaches that seek to identify the independent effect of individual variables that are statistically and mechanistically correlated. Despite its limitations, the study of Danilack et al. 12 elucidates some potentially modifiable predictors of mortality, which have been suggested by others.6,7,11,16 Most notably, there was a strong relationship between cigarette smoking and the disease states occurring as a consequence, including obstructive airway diseases and cardiac disease, and mortality. A reduction in lung function was also strongly associated with mortality, another consequence of smoking. As with the able bodied,
Risk factors for mortality in SCI
cigarette smoking is an important contributor to mortality in the SCI population. Therefore, as suggested by previous investigators,3,6,7,11 more attention should be directed to smoking cessation to achieve a reduction in the rate of respiratory complications, vascular disease, and cancer among patients with chronic SCI, an endeavor which may become even more important as this high-risk population ages.
References 1 DeVivo MJ, Stover SL, Black KJ. Prognostic factors for 12-year survival after spinal cord injury. Arch Phys Med Rehabil 1992; 73(2):156–62. 2 Yeo JD, Walsh J, Rutkowski S, Soden R, Craven M, Middleton J. Mortality following spinal cord injury. Spinal Cord 1998;36(5): 329–36. 3 Frankel HL, Coll JR, Charlifue SW, Whiteneck GG, Gardner BP, Jamous MA, et al. Long-term survival in spinal cord injury: a fifty year investigation. Spinal Cord 1998;36(4):266–74. 4 Middleton JW, Dayton A, Walsh J, Rutkowski SB, Leong G, Duong S. Life expectancy after spinal cord injury: a 50-year study. Spinal Cord 2012;50(11):803–11. 5 DeVivo MJ, Krause JS, Lammertse DP. Recent trends in mortality and causes of death among persons with spinal cord injury. Arch Phys Med Rehabil 1999;80(11):1411–9. 6 Strauss DJ, DeVivo MJ, Paculdo DR, Shavelle RM. Trends in life expectancy after spinal cord injury. Arch Phys Med Rehabil 2006; 87(8):1079–85. 7 Krause JS, Saunders LL. Risk of mortality and life expectancy after spinal cord injury: the role of health behaviors and participation. Top Spinal Cord Inj Rehabil 2010;16(2):53–60. 8 van den Berg ME, Castellote JM, de Pedro-Cuesta J, MahilloFernandez I. Survival after spinal cord injury: a systematic review. J Neurotrauma 2010;27(8):1517–28. 9 Whiteneck GG, Charlifue SW, Frankel HL, Fraser MH, Gardner BP, Gerhart KA, et al. Mortality, morbidity, and psychosocial outcomes of persons spinal cord injured more than 20 years ago. Paraplegia 1992;30(9):617–30. 10 Weaver FM, Smith B, Evans CT, Kurichi JE, Patel N, Kapur VK, et al. Outcomes of outpatient visits for acute respiratory illness in veterans with spinal cord injuries and disorders. Am J Phys Med Rehabil 2006;85(9):718–26. 11 Garshick E, Kelley A, Cohen SA, Garrison A, Tun CG, Gagnon D, et al. A prospective assessment of mortality in chronic spinal cord injury. Spinal Cord 2005;43(7):408–16. 12 Danilack VA, Stolzmann KL, Gagnon DR, Brown R, Tun CG, Morse LR, et al. Associations with chest illness and mortality in chronic spinal cord injury. J Spinal Cord Med 2014;37(6):662–9. 13 Litwin MS, McGuigan KA. Accuracy of recall in health-related quality-of-life assessment among men treated for prostate cancer. J Clin Oncol 1999;17(9):2882–8. 14 Jenkins CD, Hurst MW, Rose RM. Life changes: do people really remember? Arch Gen Psychiatry 1979;36(4):379–84. 15 Stolzmann KL, Gagnon DR, Brown R, Tun CG, Garshick E. Risk factors for chest illness in chronic spinal cord injury: a prospective study. Am J Phys Med Rehabil 2010;89(7):576–83. 16 Weaver FM, Smith B, LaVela SL, Evans CT, Ullrich P, Miskevics S, et al. Smoking behavior and delivery of evidence-based care for veterans with spinal cord injuries and disorders. J Spinal Cord Med 2011;34(1):35–45.
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