Letter to the editor: Low muscle mass in COVID-19 critically-ill patients: Prognostic significance and surrogate markers for assessment.

Dear Editor,

We read and congratulate the study by Osuna-Padilla et al. [1] which aimed to primaryly analyze muscle mass at the level of the third lumbar vertebra (L3), using the Skeletal Muscle Index (SMI) verified by computed tomography (CT) and in a secondary way to investigate the agreement and accuracy of markers from muscle mass compared to SMI, including Circumference Calf (CC), Middle Arm Circumference (MUAC), estimated fat-free mass index and Phase Angle (PhA) in critically ill patients with COVID-19. The sample consisted of 86 participants of both sexes, aged 20–71 years.

Initially, we highlight the heterogeneity of the sample, with regard to the age group of individuals. When evaluating young, adults and the elderly it is necessary to consider physiological aspects linked to changes in metabolism, capable of influencing body composition, due to the process Aging [2]. From this perspective, the researchers used the patterns directed to the classification of body mass index (IMC) according to with the World Health Organization (WHO). It would be interesting together to this, the use of the cut-off points established by Lipschitz [3] that determines the IMC considering the particularities of senescence.

We also found that the standards established by Lohman et al. [4] towards examine anthropometric aspects, as in the case of the half-wingspan throughout the sample. In this context, it should be taken into account that the models described by Lohman et al. [4] refer to the need to observe variables such as gender, race and age. Because It is known that the half wingspan is influenced by aging as well as skin color, considering that individuals blacks have longer lengths of the upper limbs compared to whites. It is therefore necessary to designate stratification criteria within the study population for the evaluation of these factors, due to the fact that skin color was not described in this study, and moreover, by involving young individuals, adults and the elderly, in order to eliminate possible bias based on the population that has been described.

We also noticed that the Shapiro Wilk test was used to verify the distribution of normality, it is worth mentioning that this is indicated for a number of amostral inferior ou igual a 50. Thus, we suggest the use of tests such as Kolmogorov Smirnov that presents higher reliability for sample analysis more than 50 individuals [5]. We emphasize that the possible inadequate choice of the test may lead to selection bias.

However, we ratified the relevance of the study by Osuna-Padilla et al. [1] and its scientific contribution to the identification of low muscle mass patients with COVID-19. Such research becomes crucial for the identification of risk factors involving the loss of muscle mass in patients restricted to bed.

Funding Statement

This work was supported by Fundação de Amparo à Ciência e Tecnologias do Estado de Pernambuco (FACEPE).

Author contributions

MLS idealized the letter, writing of the manuscript. WMAB, APSS, JHCS and VONS writing and revision of the manuscript. All authors read and approved the final version the manuscript.

Conflicts of interest

The authors have no conflicts of interest to report.