Traumatic brain injury (TBI) represents a global pandemic and is currently a leading
cause of injury related death worldwide. Unfortunately, those who survive initial
injury often suffer devastating functional, social, and economic consequences.
Among those most affected by the sequelae of TBI is the geriatric population, who
suffer mortality at significantly higher rates than other population cohorts. Furthermore,
this is particularly unfortunate given the increased incidence of head trauma among
the elderly when compared to their younger peers (Taylor et al., 2017). Advanced age
is correlated with greater rates of pre-existing medical co-morbidities, long term
use of anticoagulant and antiplatelet medications, and deconditioning. Overall, the
frailty syndrome is used to describe this progressive loss of function and debility
in the geriatric population. Frailty is significantly associated with poor outcomes
in both the elective and emergency surgery populations (Makary et al., 2010). Identification
of frailty among the geriatric trauma population may assist with risk stratification
and prognostication following TBI. However, frailty is difficult to diagnose in the
injured population, given the need to perform functional assessments of strength and
cognition that may not be feasible in the immediately injured population.
However, there is one factor of the frailty syndrome may be of particular use in this
population. Sarcopenia, which refers to a loss of muscle mass and strength, is strongly
correlated with frailty and is significantly associated with poor outcomes following
surgery (Rangel et al., 2017). Increasingly prevalent with age, sarcopenia results
in changes in gait, strength, motility, nutrition, and functional independence due
to skeletal muscle depletion. This leads to a predisposition towards falls and injury,
which, when combined with their pre-existing functional deficits, predisposes patients
to poor outcomes such as increased mortality, lengths of stay, and complications (Leeper
et al., 2016).
The causes of sarcopenia are incompletely understood and suspected to be multifactorial.
At a macroscopic level, lack of physical activity and malnutrition with associated
decreased protein intake contribute to loss of muscle mass. Systemic changes further
result in alterations in hormone production and affect the production of insulin growth
factor 1 (IGF-1), resulting in muscular atrophy (Marty et al., 2017). Increased muscular
catabolic activity may also result from enhanced oxidative stress and chronic low
grade inflammation that are associated with aging and sarcopenia, as evidenced by
elevated levels of interleukin-6 and tumor necrosis factor-α (Budui et al., 2015).
Increased levels of pro-inflammatory cytokines may further lead to neural dysfunction
and degradation, potentiating the development of sarcopenia. IGF-1, which is involved
in neuronal myelination, axonal sprouting, and neural repair, is blunted by increased
levels of tumor necrosis factor-α (Grounds, 2002; Kwon and Yoon, 2017). Motor neuron
dysfunction may result in diminished trophic factor deliver, decreased sarcomere activation,
and subsequent atrophy (Kwon and Yoon, 2017).
Regardless of its causes, the pre-dominant advantage of using sarcopenia for prognostication
is the ability to objectively identify decreased muscle volumes with widely available
imaging modalities (Leeper et al., 2016). Unlike other methods of frailty assessment
in the elderly, which require use of either subjective scoring systems, assessments
of patient function, or advanced imaging techniques better suited for the outpatient
setting, sarcopenia is most commonly diagnosed using computerized tomography (CT)
to determine muscle area in the axial place (Makary et al., 2010). This makes is use
highly advantageous in the trauma population, who are likely to be unable to perform
subjective or physical assessments and in whom imaging techniques like dual-energy
X-ray absorptiometry (DEXA) scan may not be readily available. Furthermore, CT scan
is a commonly used modality in the initial evaluation of trauma patients upon presentation,
providing readily accessible imaging without the need for additional testing.
Most commonly, sarcopenia is diagnosed using the cross-sectional area of the psoas
muscle. However, geriatric patients suffer a significant proportion of severe TBI
from low velocity accidents, such as falls from standing (Taylor et al., 2017). Routinely,
these patients are not evaluated with whole body CT given the lack of physical injury
to the torso, preventing psoas muscle measurement. Recently though, a novel method
for sarcopenia assessment was described using the cross-sectional area of the masseter
muscle (Wallace et al., 2017).
In their recent study, Wallace et al. (2017) performed a retrospective analysis of
all geriatric blunt trauma patients admitted to their trauma service to using the
cross sectional area of the masseter to diagnose sarcopenia. Cross-sectional measurements
were performed in the axial plane 2-cm below the zygomatic arch. Standard measurements
of psoas cross-sectional area were concurrently performed at the 4th vertebral body.
Both masseter and psoas muscle areas were significantly correlated (r = 0.38). However,
masseter area was significantly associated with 2-year mortality in both unadjusted
(hazard ratio (HR) 0.78, P = 0.019) and multivariate Cox proportional hazard models
(HR 0.76, P = 0.76), whereas psoas area was not (HR 0.80, P = 0.098; HR 0.68, P =
0.051). Additionally, while Kaplan-Meier analysis of both models demonstrated significant
rates of mortality in patients with the smallest muscle during the first 30 days,
only decreased masseter area was associated with significant decrease in 2-year survival.
Given these exciting results, we sought to measure masseter area in geriatric patients
with severe TBI to identify the association of sarcopenia with short term mortality
(Hu et al., 2018). We performed a retrospective review of all trauma patients admitted
to the University of Alabama at Birmingham (UAB), an American College of Surgeons
verified level 1 trauma center from 2011–2016. UAB is a major urban tertiary referral
center with approximately 4500 trauma activations annually. All patients ≥ 55 years
old with TBI were included, with TBI severity stratified using admission Glasgow Coma
Score (GCS). An admission GCS ≤ 8 was classified as severe. Patients without imaging
of the masseter muscle or with death within 24 hours due to a cause not related to
the TBI were excluded.
Cross sectional axial area of both masseter muscles was measured 2 cm below the zygomatic
arch, as previously described. Mean area was used for analysis. Sarcopenia was defined
as one standard deviation from the gender-based mean of the study population. Our
primary outcome for comparison was 30-day mortality.
During the study period, we identified 600 patients with TBI, 424 of which were classified
as severe. One hundred and eight were age ≥ 55 years and included for analysis, with
a mean age of 67.4 ± 10.6 years. Twenty-five patients were identified with sarcopenia
compared to 83 without. Mean masseter area among patients with sarcopenia was 4.55
± 1.25 cm2 for males and 3.37 ± 1.03 cm2 for females, compared to the normal averages
of 5.54 ± 1.38 cm2 and 4.41 ± 1.29 cm2, respectively.
Patients with sarcopenia were demographically matched with those without, sharing
similar median injury severity scores (26 [20–36] vs. 26 [24–34]; P = 0.82). However,
sarcopenia was associated with significantly worse outcomes. Functional outcomes appear
worse in patients with sarcopenia. Those patients without sarcopenia were significantly
more likely to be discharge to home (13.3% vs. 0%) or inpatient rehab (18.1% vs. 8.0%)
(P = 0.04). With regard to the primary objective, mortality was significantly elevated
at 30-days (80.0% vs. 50.6%, P = 0.01) and increased at 48-hours, although not significantly
(60.0% vs. 41.0%, P = 0.11). These findings were consistent on multivariate regression
analysis, with increased risk of 30-day mortality in patients with sarcopenia (odds
ratio (OR) 2.95, P = 0.045; 95% confidence interval (CI) 1.03–8.48). Similarly, increasing
masseter area was significantly associated with decreased risk of 30-day mortality
on Cox proportional hazard analysis (HR 0.78, P = 0.04; 95% CI 0.62–0.97). Kaplan-Meier
analysis demonstrated significantly decreased 30-day survival (P = 0.09) among patients
with sarcopenia compared to those without (
Figure 1
).
Figure 1
Unadjusted Kaplan-Meier 30-day survival curve for trauma patients with and without
sarcopenia.
Kaplan-Meier survival curves comparing patients with severe traumatic brain injury
and sarcopenia to those without sarcopenia. Survival time censored at 30 days following
injury. Analysis by log rank revealed significantly decreased survival among patients
with sarcopenia (P = 0.09).
Our study demonstrates that measurement of masseter area is a simple and effective
tool to assess for sarcopenia in the elderly population. Sarcopenia is significantly
associated with poor outcomes and increased short term mortality following severe
TBI. Use of masseter based measurements to identify sarcopenia is advantageous in
the geriatric patient with TBI as these patients may not undergo whole body CT scan
following low velocity injury. We feel that masseter measurements should expand to
all geriatric trauma patients as a simple and available method to identify sarcopenia
in the trauma population. Temporomandibular joint dysfunction should be investigated
as a potential confounder that may cause masseter hypertrophy. Further study should
focus on the application of aggressive treatment strategies in patients identified
with sarcopenia to determine if early, targeted intervention can improve outcomes
for this at risk population.
This work was presented at the annual 2017 meeting of The American Association for
the Surgery of Trauma.
Additional file:
Open peer review report 1.
PEER-REVIEW REPORT 1
Click here for additional data file.