Poor performance of psoas muscle index for identification of patients with higher waitlist mortality risk in cirrhosis

Abstract

BackgroundSarcopenia, characterized by low muscle mass, associates with mortality in patients with cirrhosis. Skeletal muscle area in a single computed tomography image at the level of the third lumbar vertebrate (L3) is a valid representative of whole body muscle mass. Controversy remains regarding applicability of psoas muscle to identify patients at greater risk of mortality. We aimed to determine psoas muscle index (PMI) association with skeletal muscle index (SMI) and to evaluate the capacity of PMI to predict liver transplant waitlist mortality.MethodsWe evaluated listed adult patients with cirrhosis from 2012 to 2013 at four North American liver transplant centres. From L3 computed tomography images within 3 months of listing, we determined SMI and PMI expressed by cm2/m2. Low SMI was defined as SMI <39 cm2/m2 in women and <50 cm2/m2 in men as published by us earlier. Cut‐offs for PMI to predict mortality were established using a receiver‐operating characteristic analysis. Mortality predictors were determined using competing‐risk analysis with reported results as subdistribution hazard ratios (sHRs).ResultsOf 353 waitlist candidates, 68% were men, mean age 56 ± 9 years, and Model for End‐stage Liver Disease of 16 ± 8 points. Low SMI was present more frequently in men than women (51 vs. 36%, P = 0.02). Moderately strong correlation between SMI and PMI was observed (r > 0.7, P < 0.001). Low PMI (males < 5.1 cm2/m2; females < 4.3 cm2/m2) yielded poor and moderate concordance with low SMI in men and women, respectively (Kappa coefficient 0.31 and 0.63). SMI (39 ± 9 vs. 43 ± 7 cm2/m2; P = 0.009) and PMI (4.4 ± 1.3 vs. 5.2 ± 1.1 cm2/m2; P = 0.001) were lower in women who died and/or were delisted (compared with non‐deceased patients) whereas men who died and/or were delisted had only lower SMI (47 ± 7 vs. 51 ± 9 cm2/m2; P = 0.003), but not PMI compared with non‐deceased patients. In women, both SMI (sHR 0.94, P = 0.048) and PMI (sHR 0.58, P = 0.002) were predictors of mortality, while in men, SMI was significant (sHR 0.95, P = 0.001) and PMI showed a trend to be (sHR 0.85, P = 0.09) associated with mortality. Overall, 104 patients (29%) were misclassified between SMI and PMI categories. Using PMI cut‐offs, 66% and 28% of low SMI men and women, who have a higher risk of mortality, were incorrectly classified as low risk.ConclusionsSkeletal muscle index is a more complete and robust measurement than PMI, especially in men with cirrhosis. Low PMI identifies an incomplete subset of patients at increased risk of mortality indicated by low SMI. Given the poor performance of PMI, SMI should not be substituted by PMI.

Continued muscle loss increases mortality in cirrhosis: Impact of aetiology of liver disease

“…Our use of a contemporaneous group of age‐matched subjects without documented disorders that alter muscle mass showed that the standardized rate of muscle loss (either absolute or percentage) in cirrhosis of any aetiology is significantly greater than that due to age alone. Unlike earlier reports, in the present study we observed that all three muscle groups studied had similar predictive value for outcomes. We therefore believe that the psoas muscle area alone can be used as an indicator of muscle mass due to the ease of measurement.…”

Sarcopenia in Chronic Liver Disease: Impact on Outcomes

“…However, others have used L4 as a landmark . Furthermore, other studies have cited SMM area as a more complete measure than PMA alone because it is closely related to total body protein and wait‐list mortality . PMT as an alternative indicator to assess for sarcopenia has also been proposed, but it requires further validation .…”

“…(47) Furthermore, other studies have cited SMM area as a more complete measure than PMA alone because it is closely related to total body protein and wait-list mortality. (48,49) PMT as an alternative indicator to assess for sarcopenia has also been proposed, but it requires further validation. (32) Use of cross-sectional CT/MRI, segmental DEXA using appendicular measures, and phase angle BIA have been shown to be less influenced by overhydration than whole body measures.…”

A North American Expert Opinion Statement on Sarcopenia in Liver Transplantation

“…Several key questions remain regarding the use of CT-based estimation of skeletal muscle mass, including the use of values below specific percentiles (i.e., 5th percentile) of age-and sex-matched population or optimal cut-points for mortality discrimination, sensitivity of changes over time, and the validity of measurement of psoas alone versus the total muscle area. (21)…”

“…In addition, low PMI identifies an incomplete subset of patients at increased risk of mortality indicated by low SMI. (21) Although sarcopenia has classically been associated with increased mortality in both men and women with cirrhosis, emerging evidence suggests that sarcopenia is associated with disproportionately higher rates of mortality in men as compared with women. (27) This emphasizes the importance of survival analysis stratification by sex rather than simply adjusting multivariable models for sex.…”