How to improve life expectancy after spinal cord injury - Part 2
Introduction and recap
In the first article in this series, we described how the lifespan of our general population increased on average as we moved through the first half of the 20th century. This was largely due to improved public health measures and the arrival of antibiotics. At present, we no longer see lifespan increasing and what is worse, many of us spend the last years of life in poor health and subject to chronic conditions that are associated with ageing. These conditions are:-
Heart disease
Cancer
Neurodegenerative disease
Type 2 diabetes and related metabolic dysfunction
These conditions are highly correlated with age and approximately 80% of the population will succumb to them. To some extent, they may have common causes that we would need to dig deep to uncover. In particular, metabolic dysfunction seems to be a precursor to all these other diseases.
In search of prevention strategies
By reducing our risk of these diseases we are more likely to have a longer life, but a more useful aim is to increase our healthspan: not just extending the length of life, but the health with which to enjoy it. This is a worthy goal for all of us whether the spinal cord is injured or not.
The logical key to improving healthspan is to do what we can to tackle metabolic dysfunction and aspects of heart disease, cancer and neurodegenerative disease that we might be able to influence.
Medical science needs to shift much more from trying to fix sick people and move to prevention if we are to rely upon it to contribute much to enhancing healthspan. With perhaps the exception of cardiovascular disease, medicine is not good enough yet at prevention. We have to take some personal responsibility for reducing our disease risk. As we will learn the key for all of us is to change how we exercise, what we eat, and how we sleep.
Studying populations
To see trends within a population we need to work with large numbers and observe them over many years. You can imagine some methodological difficulties in doing this. Of course, you could imagine assuming that people are pretty much the same so that on average the observed trends are relevant to the population and individuals equally. However, we know that our population is not going to be homogenous and we probably we should account at least for differences in gender, area of residence, socioeconomic status and much more. Even when we pay attention to these things our observations might uncover some interesting correlations - but this is not the same as finding causations (that would allow you to say that individuals live longer because ...)
These difficulties only become greater when studying a population of spinal cord-injured persons where there are more confounding influences such as severity and level of injury (ASIA score), age at the time of injury and whether the spinal cord injury was traumatic or not. There is no certainly such thing as a homogeneous group of persons with spinal cord injuries.
Literature on survival and lifespan following SCI
Let's look at the literature on lifespan following an SCI. These studies were carried out in various countries and represent various study timeframes.
Middleton et al (2012) studied a cohort of incident cases from 1955 to 2006 in a specialist SCI unit in Australia. The objective was to analyse acute and long-term mortality, estimate life expectancy and identify survival patterns of individuals experiencing traumatic spinal cord injury.
Data for patients with traumatic SCI admitted to a spinal unit in Sydney, Australia between January 1955 and June 2006 were collated and deaths were confirmed. Cumulative survival probability was estimated using life-table techniques and mortality rates were calculated from the number of deaths and aggregate years of exposure. Standardised mortality ratios (SMRs) were estimated from the ratio of observed to expected number of deaths. Life expectancy was then estimated using adjusted attained age-specific mortality rates.
From 2014 persons, 88 persons with tetraplegia (8.2%) and 38 persons with paraplegia (4.1%) died within 12 months of injury, most often with complete C1–4 tetraplegia. Among first-year survivors, overall 40-year survival rates were 47 and 62% for persons with tetraplegia and paraplegia, respectively. The most significant increases in mortality were seen in those with tetraplegia and ASIA grades A–C lesions, with SMRs between 5.4 and 9.0 for people ⩽50 years, reducing with advancing attained age. Estimated life expectancies from 25 to 65 years ranged between 69–64%, 74–65%, 88–91% and 97–96% for C1–4 AIS A–C, C5–8 A–C, T1–S5 A–C and all AIS D lesions, respectively.
Survival was related strongly to the extent of neurological impairment. The authors suggest that future research should focus on identifying contextual factors, personal or environmental, that may contribute to the reduced life expectancy after SCI.
DeVivo et al (2022) set out to identify via a cohort study the trends in causes of death after SCI that could enhance understanding of why life expectancy after SCI has not improved in the last 3 decades.
Individuals with traumatic SCI (N=49,266) enrolled in the SCI Collaborative Survival Study Database between 1973 and 2017. Age-standardized cause-specific SCI mortality rates and 95% confidence intervals were calculated for 5-time intervals (1960-1979, 1980-1989, 1990-1999, 2000-2009, and 2010-2017).
A total of 17,249 deaths occurred in 797,226 person-years of follow-up.
Since 2010, the highest mortality rate was for respiratory diseases, followed by heart disease, cancer, infective and parasitic diseases (primarily septicemia), and unintentional injuries.
Mortality rates for respiratory diseases, cancer, stroke, urinary diseases, and digestive diseases, initially decreased significantly but remained relatively stable since 1980, whereas essentially no progress occurred for infective and parasitic diseases.
Mortality rates for heart disease, pulmonary embolus, and suicide decreased significantly throughout the entire study period but were offset by increases in mortality rates for endocrine (primarily diabetes), nutritional, and metabolic diseases, as well as unintentional injuries.
From 2010 to 2017, the overall age-standardized mortality rate was 3 times higher for individuals with SCI than the general population, ranging from 27% higher for cancer to 9 times higher for infective and parasitic diseases.
The authors conclude that Improving life expectancy after SCI will require: (1) reducing mortality rates from respiratory diseases and septicemia that have remained high, (2) reversing current trends in diabetes and unintentional injury deaths, and (3) continuing to reduce mortality from heart disease and other leading causes.
Closer to home, a 70-year observational study conducted in the UK (Savic et al, 2017) has reported the trends in survival after traumatic spinal cord injury. The team studied 5,483 patients injured between 1943 and 2010 and observed a significant improvement in life expectancy between 1950 and 1980, after which survival plateaued, followed by a small improvement after 2010. The team also used the data to provide current life expectancy estimates for individuals with spinal cord injury, which range from 18.4% to 88.4% compared with the general population, depending on sex, current age and type of injury. The study took place at the two oldest British spinal injury centres at Stoke Mandeville and Southport Hospital.
Buzzell et al (2019) investigated survival and life expectancy after non-traumatic spinal cord injury in Switzerland according to aetiology. Within this study, a variety of categories were used: “degenerative disc disorders,” “infection,” “vascular disorders,” “benign tumours,” “malignant tumours,” “unspecified tumours,” and “other.” The “other” category represented a mixed group of individuals with non-traumatic SCIs that developed from unclear origins, metabolic disorders, inflammatory diseases, and radiation-related causes. A category of “unspecified tumours” was included, given that several participants had neoplasms of an unknown origin. SCI-related characteristics included in the present study were: lesion level, lesion completeness, and SCI type. Cases due to congenital disorders (e.g., spina bifida) or progressive neurodegenerative disorders (e.g., multiple sclerosis) were excluded.
One thousand four hundred and fifty individuals were admitted to first rehabilitation between 1990 and 2011, contributing to 6137 cumulative person-years at risk and 528 deaths.
Survival and life expectancy estimates were found to be highly variable between etiological groups, indicating a need for a heterogeneous clinical approach and dynamic healthcare provisions for this growing population.
Krause et al (2005) carried out a longitudinal survey to investigate the natural course of changes in activity patterns, health indicators, life satisfaction, and adjustment over 25 years among people with spinal cord injury in the USA. The preliminary data were collected from a Midwestern United States university hospital, whereas the follow-up data were collected at a large Southeastern United States rehabilitation hospital. The Life Situation Questionnaire was used to identify changes in education/employment, activities, medical treatments, adjustment, and life satisfaction.
Adjustment scores, satisfaction with employment, satisfaction with finances, years of education, and employment indicators significantly improved over time. In contrast, satisfaction with sex life, satisfaction with health, and the number of weekly visitors significantly decreased and the number of nonroutine medical visits and days hospitalized within 2 years before the study significantly increased over the 25 years.
Given the mixed pattern of favourable and unfavourable changes, the findings challenge the assumption that ageing will inevitably be associated with the overall decline in outcomes and quality of life.
Krause et al (2010) set out to identify the relationships between health behaviours and participation and life expectancy after spinal cord injury while controlling for biographic and injury factors. Data for this prospective cohort study were collected by mailed survey. Participants included 1,361 adults with traumatic SCI, 1 or more years post-injury. Participants were enrolled an average of 9.7 years after injury, and mortality was determined at the end of 2007. There were 294 deaths by follow-up. Life expectancy was calculated utilizing person-years and logistic regression. Studies of health behaviours and mortality after SCI are rare. Preliminary studies used the retrospective analysis or assumed maladaptive behaviours based on causes of death. For instance, studies of causes of death showed that 28% of deaths appeared highly preventable, resulting from pressure ulcers, sepsis, other infections, or accidental deaths. A violent aetiology was linked to greater mortality, and this can be used to identify individuals at greater risk of mortality.
Interventions that successfully eliminate smoking, reduce binge drinking, reduce psychotropic medication use, and promote activities outside the home have promise for improving longevity.
Conclusion
Age-related medical conditions are the greatest contributors to death in our society. Though spinal cord injury may reduce life expectancy, it does not have to reduce the quality of life throughout that life. Taking proactive, preventative measures such as leading a balanced lifestyle and getting regular check-ups with one’s primary care physician can be incredibly beneficial for everyone—those with spinal cord injury and those without. As individuals, it is up to us to take control and make sure we are about creating a longevity narrative made up for our strength and health rather than illness or fragility. After all, healthspan matters as much as lifespan.
In the next article in the series, we look at strategy and tactics for extending our healthspan
References
DeVivo, MJ; Chen, Y; Wen, H (2022). Cause of death trends among persons with spinal cord injury in the United States: 1960-2017. Archives of physical medicine and Rehabilitation. Volume 103, Issue 4, April 2022, Pages 634-641. https://www.sciencedirect.com/science/article/pii/S000399932101563X
Savic, G., DeVivo, M., Frankel, H. et al. (2017). Long-term survival after traumatic spinal cord injury: a 70-year British study. Spinal Cord 55, 651–658 (2017). https://doi.org/10.1038/sc.2017.23
Buzzell, A., Chamberlain, J.D., Gmünder, H.P. et al. (2019). Survival after non-traumatic spinal cord injury: evidence from a population-based rehabilitation cohort in Switzerland. Spinal Cord 57, 267–275 (2019). https://doi.org/10.1038/s41393-018-0212-x
Krause J. Broderick L. (2005). A 25-year longitudinal study of the natural course of aging after spinal cord injury. Spinal Cord. 2005; 43: 349-356
Krause JS, Saunders LL. (2010). Risk of Mortality and Life Expectancy After Spinal Cord Injury: The Role of Health Behaviors and Participation. Top Spinal Cord Inj Rehabil. 2010 Fall;16(2):53-60. doi: 10.1310/sci1602-53. PMID: 21960734; PMCID: PMC3181073.
Middleton, J., Dayton, A., Walsh, J. et al. (2012). Life expectancy after spinal cord injury: a 50-year study. Spinal Cord 50, 803–811 (2012). https://doi.org/10.1038/sc.2012.55