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

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.

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.

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).

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.