Background LAM is a rare disease of women in which abnormal smooth muscle cells invade and destroy particularly the lungs and lymphatics. We wanted to relate the progression of the disease with presenting clinical features and to determine rate of decline of lung function in patients to improve prognostic predictions and stratify patients for clinical trials.
Methods Clinical features and pulmonary function test (PFT) data were collected from 125 patients with a definitive diagnosis of LAM by European Respiratory Society Criteria receiving care at the National Centre for LAM. Ethical approval for use of patient data was obtained and patients gave informed consent. 74 of these patients with more than two sets of PFTs formed the prospective cohort. Patients were grouped into degree of lung function impairment based on FEV1 or DLCO at first presentation: unimpaired; PFTs >80% predicted, mild; 61%-80%, moderate; 40%–60%, severe; <40%.
Results The median follow-up period was 28.5 months (range 3–262). PFTs declined as the disease progressed (figure shows all prospective FEV1 measurements from presentation). Mean changes for FEV1 were –49.68 ml/yr, FVC –44 ml/yr, and DLCO –0.07 mmol/min/kPa/yr. Rate of change in FEV1 varied between patients with different degrees of lung function impairment at first presentation with change in FEV1 within the groups being: unimpaired –84 ml/yr, mild –32 ml/yr, moderate –59 ml/yr and severe –24 ml/yr.
Conclusion The rate of decline of FEV1 in this cohort was slower than in previous retrospective studies of patients with LAM. Change in FEV1 varied with degree of lung function impairment being more rapid in those with early disease ie. well preserved lung function at diagnosis. Clinical features at onset may be associated with rate of progression of LAM. These data may be helpful in advising patients on prognosis and designing clinical trials.