The application of near infrared spectroscopy during exercise and recovery in children with dermatomyositis: a pilot study.

Juvenile dermatomyositis (JDM) is an idiopathic chronic auto-immune disease in
childhood in which the microvasculature of the skin and skeletal muscles is
targeted by the immune system. This results in reduced exercise tolerance due
to abnormally thickened endothelial walls of the intermuscular capillaries,
arterioles, and veins, decreased capillary bed volume, and impaired perfusion
in muscles (1-7).
For the assessment of the clinical course of the disease and for the
evaluation of the effects of interventions and therapies, it is important to
have an objective longitudinal perspective. Since the cause of the exercise
intolerance in JDM is thought to be situated in the microvasculature of muscle
tissue, near infrared spectroscopy (NIRS) could be a possible tool for this
need. In previous studies, it was shown that it is possible to detect with NIRS
abnormal muscle oxygenation patterns during exercise and recovery in patients
with different levels of exercise intolerance (8). However, the application of
NIRS during exercise and recovery in the study of children with dermatomyositis
is not determined at present.
In the proposed pilot study, NIRS measurements will be combined with a
cardiopulmonary exercise test (CPET) on a cycle ergometer. NIRS measurements
will be done on the vastus medialis (VM) and vastus lateralis (VL) muscle
during a single test. The data of patients with JDM will be compared with those
of age- and gender matched patients with juvenile idiopathic arthritis (JIA)
and healthy children.

The objective of this pilot study is to provide information about the
usefulness of NIRS in the study of patients with JDM in the test configuration
as described in the protocol. For this purpose, the microvascular oxygenation
and hemodynamics in thigh muscle of patients with JDM and subjects in the
control groups will be qualitatively assessed during rest, incremental
exercise, and recovery with continuous wave NIRS. In this way, abnormal
features could be observed. Furthermore, the microvascular function of the
muscle will be quantitatively assessed by calculation of the half-recovery time
of deoxygenated hemoglobin (T1/2) during recovery. This parameter is related to
microvascular function. These values will be compared with those of patients
with JIA and healthy subjects.
Since it is thought that patients with JDM have impaired perfusion in
muscle tissue, it is hypothesised that patients with JDM show a higher T1/2.
Moreover, the T1/2 values will be linked with other measures obtained during
the CPET. Finally, microvascular oxygenation response data obtained from the VM
and VL muscle will be compared to each other. Together, these examinations
provide information about the usefulness of NIRS in the study of patients with
JDM in the test configuration as described in the protocol.

In this cross-sectional pilot study, thigh muscles of a heterogeneous
population of patients with JDM, patients with JIA, and healthy young subjects
will be measured during rest, incremental cycling exercise, and recovery with
NIRS.

For the healthy children, the load is performing a CPET with NIRS measurements
once only. This test produces interesting results for the children and their
parents. The risks for a CPET are minimal and NIRS measurements are safe as
well. For the patient population, the only additional load is the measurement
done with NIRS.
Children show different physiological responses to exercise compared to
adults. Furthermore, the pathophysiology of dermatomyositis shows differences
between children and adults. For these reasons, it is important to consider
adult and juvenile dermatomyositis separately when studying the application of
NIRS during exercise and recovery in dermatomyositis.