Discussion
Juvenile CTD is accompanied by high morbidity and mortality and can
disturb any organs. Yet, ILD is an uncommon but it is one of the most
significant complication of CTD 6,35. The serum
KL-6 level is secreted by type II alveolar epithelium and elevated with
lung tissue regeneration 36-38. KL-6, which is
a sensitive and specific marker for the development of ILD34,39-41. As a result of this solid review, our
study aims to evaluate the correlation between serum KL-6 levels with
both presence of interstitial lung disease (ILD) and its severity in
connective tissue diseased children, directing to early detection and
better management of interstitial lung disease in CTD children.
Regarding to KL-6 serum level and its relationship with severity of ILD
and other measured parameters, our study concluded that the KL-6 levels
were increased in the CTD with ILD patients compared to the CTD without
ILD and control groups. At the cut-off value of serum KL-6 to
distinguish ILD was 63.4 U/ml, with sensitivity of 95.2%, specificity
of 89.7%, positive predictive value of 83.26% and negative predictive
value of 97.2%. Similar results were reported by Oguz et al. who
detected increased KL-6 levels in CTD with ILD patients than patients
without ILD and control groups 6 . In the same
way, Fathi et al. reported that the KL-6 levels were increase in 12
patients with polymyositis and DM + ILD 42 .
Furthermore, Fukaya et al. presented that the KL-6 level is a marker of
ILD in CTD, and also indicate disease activation and follow up43. In that study, no correlation was found
between disease duration and KL-6 level, which disagree with our study,
as we concluded that there is a significant direct correlation between
disease period and KL-6 level.
Regarding to associations between serum levels of KL-6 and spirometry
(PFT) parameters, our study showed that there is a significant inverse
correlation between KL-6 serum level and pulmonary function parameters
(predicted FEV1 and FVC%) Matching to our study, the PFT is used to
detect respiratory complication in CTD studies carried out by44-46. Although it is a non-invasive test that
can be repeated easily, it requires collaboration from the patient and
is difficult to do in younger children. In a study of polymyositis and
DM patients, an inverse correlation was found between KL-6 serum level
and PFT parameters in patients with ILD 42.moreover, Hu et al. stated that polymyositis and DM patients with ILD
had a greater KL-6 levels than patients without ILD, and they also found
that the KL-6 levels were significantly inversely correlated with FEV1
and FVC% 38. Furthermore, Cao et al. proved
that the elevated serum KL-6 correlates with the worsening of lung
function of SSC–ILD patients 47.
It is challenging to identify strong correlation between ILD and
different CTD types because of the small number of ILD patients. Also,
the study sample was diverse, and we did not assess the active CTD
exacerbation. Furthermore, we did not do HRCT to asymptomatic patients
to reduce radiation exposure and thus asymptomatic ILD patients might be
skipped. This lowers the power of our work.