Pediatric pulmonary multisystem langerhans cell histiocytosis: does lung lesion severity affect the outcome?

Background The pediatric pulmonary multisystem Langerhans cell histiocytosis (PPM LCH) is associated with either low risk or high risk organ(s). The nodulo-cystic lung lesions although pathognomonic, yet are very variable in severity and remain a source of controversy in certifying pulmonary LCH diagnosis. The study aimed to examine the prognostic value of clinical respiratory manifestations and radiological lung lesions severity. This is through associating a CT chest triad of bilateral, extensive and diffuse lesions. It is a retrospective study of 350 LCH patients who received systemic treatment at Children's Cancer Hospital Egypt during the period from 2007 to 2020.Results Sixty-seven patients (67/350-19.1%) had PPM LCH at presentation. Severe lung lesions were present in 24 of them. The median follow-up period was 61 months (IQR: 3.4-8.3). The 5-year overall survival (OS) and event free survival (EFS) was 89% and 56.6% respectively. The EFS, for severe radiological lesions triad was 38% +/- 20.7 versus 66% +/- 16.2 for non-severe lesions triad p 0.002, while for presence of chest X-ray changes 27% +/- 22.344 versus absence of chest X ray changes 66% +/- 14.7 p 0.001, for clinical respiratory manifestations 13% +/- 13.9 versus none 62% +/- 22.9 p < 0.001, for RO- with severe lung lesions 47% +/- 30.4 versus RO- without severe lung lesions 69% +/- 5.9 p 0.04. There was a tendency for the independent prognostic impact of severe lung involvement; aHR = 1.7 (95% CI 0.92-3.13, p = 0.09).Conclusion Although the lung is a low -risk organ per se in LCH, our study demonstrates a non negligeable prognostic impact of severe lung involvement in the risk stratification of pediatric LCH. This warrants further study and external validation.