Two forced expiratory volume in 1 s trajectories with distinct prognoses in pulmonary Langerhans cell histiocytosis.

Background: Lung function outcomes in pulmonary Langerhans cell histiocytosis (PLCH) patients are variable and difficult to predict. Our goal was to identify different forced expiratory volume in 1 s (FEV₁) trajectories in these patients during long-term follow-up.

Methods: All newly diagnosed adult PLCH patients seen between January 2004 and April 2018 were eligible for inclusion in our prospective cohort. The primary end-point was the identification of FEV₁ trajectories using a joint latent class model for longitudinal and time-to-event data. Internal validation was performed via bootstrapping.

Results: Among the 191 patients included (mean age of 39±12 years, 59% females, 96% current smokers), who were followed for a median of 5.1 years (interquartile range 3.2-6.0), two FEV₁ trajectories were identified. Patients with trajectory 1 (n=157, 82.2%) were characterised by a normal FEV₁ at diagnosis (mean predicted value (pred) of 95±3%) that remained stable over time (annual variation of 0.2% pred, 95% CI -0.8-0.4). Patients with trajectory 2 (n=34, 17.8%) had a decreased initial FEV₁ (63±7% pred) and an annual decrease of -1.8% pred (-3.4--0.2). Trajectory 2 was associated with increased mortality (hazard ratio 9.46, 95% CI 1.24-72.2; p=0.03).

Conclusions: FEV₁ remained stable in most PLCH patients, but the subgroup of patients that experienced a significant decrease in FEV₁ over time had a poorer prognosis. These patients should be closely monitored for early therapeutic intervention. These results need to be confirmed in an external validation cohort.