Sarcopenia in Children? A Repechage or ‘Better Late Than Never’
Sarah Razaq, FCPS1, Murat Kara, MD2,
Levent Ӧzcakar MD, Professor2
1 Department of Physical medicine & rehabilitation,
Combined Military Hospital, Quetta, Pakistan
2 Hacettepe University Medical School, Department of
Physical and Rehabilitation Medicien, Ankara, Turkey
* Correspondence to:
Sarah Razaq, FCPS, Department of physical medicine & Rehabilitation,
Combined Military Hospital, Quetta, 87300, Pakistan
Tel.: 0092-3336123022, Email: docsrazaq@gmail.com
Text word count 529;
Abstract word count: Not included;
Brief running title: Sarcopenia in children
Key words: Sarcopenia, children, Muscle mass
Tables: Nil
Figures: Nil
Dear Editor,
With much interest, we have gone through the recently published article
(Sarcopenia is a prognostic outcome marker in children with high-risk
hepatoblastoma) by Ritz et al.1. We wish to
congratulate the authors for measuring total psoas muscle area as a
prognostic risk factor in children with hepatoblastoma. They have
measured the cross-sectional muscle area at two distinct lumbar levels
(L3-4 and L4-5) on computed tomography or magnetic resonance imaging
using a freely-available online z -score calculator
tool.2
Herewith, our point of concern is two-fold; we would like to comment on
the use of the term ‘sarcopenia’ in children and on the lack of
functional evaluation. Regarding the former, it is well-known that
sarcopenia is age-related loss of muscle mass and muscle function, which
ensues as early as in 5th decade (at middle age) but
not in children or young adults. Therefore, we need to note that there
is a misunderstanding as regards the definition. Sarcopenia was first
described in 1989 as an age-related decline in lean body mass affecting
mobility, nutritional status, and independence.3 Of
note, it is not muscle wasting or atrophy (due to immobilization,
malnutrition, infection, cachexia or any adverse treatment effect) alone
and should be accompanied by loss of muscle function as well. Herein,
muscle function progressively deteriorates due to motoneuron loss that
is not adequately compensated by reinnervation of muscle fibers by the
remaining motoneurons.4 The aging-related
denervation/reinnervation process has a strong impact on the
quantitative changes in muscle (e.g. muscle fiber loss and atrophy),
resulting in overall loss of muscle mass and muscle
function.4
Second, the reduced muscle mass in the absence of functional evaluation
can/should not be labelled as sarcopenia. Although for decades, this
term has been used to describe the loss of muscle mass alone without
reference to function, and is still being used in some cancer and other
disease-related sarcopenia studies;5 after 2010, a big
milestone i.e. muscle function (loss) was introduced into the
concept/definition of sarcopenia.6 This new focus on
muscle function is usually defined by muscle strength and power (or
physical performance) and these parameters were shown to be more
powerful predictors of clinical outcomes than muscle mass
alone.7 Hence, similar to adults, performance
evaluation can possibly be carried out via measuring grip strength (for
muscle function) and anterior thigh muscle thickness (for muscle mass)
in children as well.8 Of additional note, the other
important milestone has been the recognition of “age-related sarcopenia
(M62.84)” as an independent condition i.e. different from “muscle
wasting and atrophy, not elsewhere classified (M62.5)” according to the
International Classification of Diseases-10 code in
2016.9
Lastly, muscle loss due to aging (i.e. sarcopenia), immobilization or
malnutrition (i.e. muscle wasting and atrophy) is not uniform throughout
the body, and it is noteworthy that anterior thigh muscles (rich in type
2 fibers) undergo atrophy earlier than the other muscle
groups.8 Therefore, aside from promptly defining the
pertinent clinical scenarios, we emphasize the use of basic but vital
functional test (i.e. grip strength) together with the anterior thigh
muscle thickness measurements (by ultrasound) in their assessments. This
way, loss of muscle mass and function as well as the overall health
status can accurately be managed in children.10