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INTRODUCTION
Sarcopenia (Greek ‘sarx’ or flesh + ‘penia’ or loss) is defined as a progressive and generalized skeletal muscle disorder [5]. It is an important marker of nutritional and physical status and overall health [6,11]. It is currently recognized as a muscle disease and considered an independent condition based on the International Classification of Diseases, 10th clinical edition [1,20]. Clinically, it is associated with cardiovascular, respiratory, and malignant diseases [4,8,15]. Sarcopenia is also associated with an individual’s quality of life and mortality [3,9].
Among the many methods available to assess muscle status, the measurement of psoas muscle area (PMA) using computed tomography (CT) is well known. Reports have related PMA to mortality and the quality of life in several critical patients [7,10,19]. CT measurement of the masseter muscle area (MMA) is an alternative method to analyze muscle status. The masseter muscle is associated with nutritional disorders such as obesity and also with geriatric conditions [14]. It is also associated with the patient’s cerebrovascular prognosis [16,17]. Hu et al. [13] reported that MMA was associated with early mortality in patients with severe traumatic brain injury (TBI).
Both PMA and MMA are proven prognostic markers in various diseases. However, evidence to suggest the relative superiority of each muscle as a prognostic marker is inadequate. Therefore, the present study was undertaken to compare the prognostic values of both markers including the odds ratio and correlation coefficient in inpatients with TBI. A comprehensive analysis of qualitative and quantitative parameters is presented.
MATERIALS AND METHODS
This retrospective study was approved by the Institutinal Review Board of Uijeongbu St. Mary's Hospital (UC20RISI0093), and the requirement for informed consent was waived. Patients with TBI visiting the regional trauma center between January 2017 and December 2018 were selected. Their medical information was gathered via retrospective chart review. General parameters including age, sex, height, weight, length of hospital stay, and trauma-related factors such as intubation, operation, Glasgow coma scale (GCS) score, abbreviated injury score (AIS), and injury severity score (ISS) were evaluated. Glasgow outcome scale (GOS) scores and mortality were analyzed together to determine the clinical outcomes. Patients with endotracheal intubation and scoring 8 or less on the GCS were regarded as having a severe TBI and compared to those with scores of 9 or higher on the GCS. Patient body mass index (BMI) was calculated and those with a BMI higher than 25 were regarded as obese.
Initially, CT was used to perform the muscle measurements. Common sites were used for the anthropometric studies, as described previously. The cross-sectional area of the psoas muscle was measured at the level of the third lumbar vertebral body bilaterally as the PMA [12]. The cross-sectional area of the masseter muscle was measured 2 cm below the zygomatic arch bilaterally as the MMA [18]. The psoas muscle index (PMI) and the masseter muscle index (MMI) were calculated by dividing both muscle areas by height in meters squared (cm2/m2). Patients with proper CT images were included in the study. Patients with tilted CT images or image artifacts were excluded. Patients with injured muscles or nearby bony structures were also excluded.
Patients with major TBI were selected based on an AIS of 4 or 5. Patients with an AIS of 4 or 5 at the chest, abdomen, or extremity were excluded to reduce bias associated with other conditions. Patients younger than 19 years and those with missing data were also excluded. Additionally, patients with a hospital stay of fewer than 2 days were excluded.
Comprehensive analyses were planned. Mortality was used as a qualitative outcome and GOS scores were used as a quantitative outcome. Initially, the patients were separated into two groups, survival and mortality, and their medical records were analyzed. An independent t-test was used for quantitative analysis, and chi-squared tests were used for qualitative analysis. Logistic regression analysis was performed to verify the risk factors. Bivariate correlation analysis of both muscle indices and GOS scores was conducted. Correlation coefficients were calculated after adjustment for age, BMI, AIS, and ISS. Additionally, multiple regression analysis was performed. All statistical analyses were performed using IBM SPSS Statistics for Windows, version 25.0 (IBM Corp., Armonk, NY, USA).
RESULTS
A total of 357 TBI patients had an AIS score of 4–5. Among them, 263 patients were suspected of having major trauma and underwent both brain and torso CT (chest + abdominopelvic CT). Two hundred and forty-three patients with proper CT images and 226 patients without injury to the chest or abdomen, or extremity AIS scores of 4–5, were selected. Twenty patients were excluded due to age, and seven patients were excluded due to missing data. Additionally, 20 patients were excluded for missing data. The patient selection process is summarized in Fig. 1.
A total of 179 patients were finally included in the statistical analyses. The mean patient age was 58.0 years. The study included 147 male patients (82.1%). The patient population was as follows : 51 patients with obesity (28.5%), 64 patients with severe TBI (35.8%), and 92 patients treated with neurosurgery (51.4%). The mean PMA and MMA values were 16.5 cm2 and 9.8 cm2, respectively. The mean PMI and MMI values were 5.8 and 3.5 cm2/m2, respectively. Mortality was recorded in 30 patients (16.8%). The mean GOS score was 3.7. Other basic information is summarized in Table 1.
The parameters related to mortality, which was a qualitative study outcome, were analyzed. PMA (16.9 vs. 14.4 cm2, p=0.028) and PMI (5.9 vs. 5.1 cm2/m2, p=0.004) showed statistically significant differences between the survival and mortality groups, as did patients with endotracheal intubation and scoring 8 or less on the GCS (p<0.001). Also, the external and facial AIS values differed statistically. The mortality analysis is summarized in Table 2. A logistic regression analysis of mortality parameters is presented in Table 3. Patients with endotracheal intubation and scoring 8 or less on the GCS was statistically associated with mortality. PMI was also a statistically significant risk factor for mortality (B=-0.336; p=0.023; odds ratio, 0.715; 95% confidence interval, 0.535–0.954). The mean MMA and MMI decreased in the mortality group, but the difference was not significant.
Analysis of the GOS scores was performed and the results were defined as a quantitative outcome. Bivariate correlation analysis showed a statistical correlation between PMI and GOS (correlation coefficient, 0.168; p=0.003). Partial correlation analyses were performed after adjustment for age, BMI, AIS, and ISS. PMI was correlated with GOS scores after multiple adjustments, but the MMI was not significantly correlated (Table 4). The results of the multiple regression analysis are presented in Table 5 (R2=0.048). PMI showed a statistically significant association with GOS (B=0.184, p=0.004, variation inflation factor 1.001).
DISCUSSION
The present study is unique for several reasons. First, the study goal was uncommon in that it was planned to compare the relative superiority of the psoas muscle (PM) and masseter muscle (MM), which are well-known prognostic markers.
Second, the study selected patients with severe TBI (AIS 4 or 5). Patients with other severe injuries were excluded. To reduce the impact of other injuries, patients with AIS scores of 4 or 5 at the chest, abdomen, or extremity were excluded. Additionally, patients with hospital stays of longer than 2 days were selected. Dead trauma patients during this period usually had severe, incurable injuries and their mortality might be inevitable. In addition, the guardians of some patients wanted patients transferred to another hospital. These patients were regarded as improper candidates for the analysis and excluded from the study. Consequently, the study included patients with serious TBI and reduced the possibility of bias, although the number of analyzed patients was decreased.
Third, comprehensive analyses of qualitative and quantitative parameters were planned. A similar study of PM and MM analysis was reported previously [21]. Both parameters were analyzed based on mortality alone, which was a qualitative parameter. However, this study analyzed mortality and GOS scores comprehensively.
The AIS face and external scores showed a statistical difference. However, the mean AIS score was less than 1 point, indicating a very minor injury. Those injuries were too minor and might have had an insignificant effect on mortality or GOS scores.
However, the authors could not define or analyze sarcopenia in the present study. The initial target for analysis was not sarcopenia but involved both the PM and MM. Muscle strength and physical performance were not assessed because patient cooperation was hindered by their TBI. Further, it has been reported that sarcopenia cannot be represented by a single muscle [2]. Nevertheless, the relationship between both muscles and the prognosis of patients with TBI was determined statistically. Further study is needed to diagnose sarcopenia in a larger population of patients.
CONCLUSION
A larger PMA was associated with statistically significant survival outcomes and better GOS scores and showed superiority as a prognostic marker. Although TBI severity was the most significant mortality parameter, PMI was statistically significant in various analyses, suggesting that the PMI can be used to predict the prognosis of patients with TBI, whereas the MM showed no statistically significant results and was not comparable to the PM. Consequently, the PM showed its superiority over MM as a prognostic marker for TBI. Further analyses with a larger number of patients might show different results because this study had a relatively low number of participants. Additional parameters and more precise settings can yield better outcomes and increase our understanding of the relationship between sarcopenia and TBI.
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