The epidemiology of lymphangioleiomyomatosis in Japan: A nationwide cross-sectional study of presenting features and prognostic factors

Background and objectives: To evaluate the characteristics and prognostic factors of Japanese patients with lymphangioleiomyomatosis (LAM). Methods: A nationwide survey to identify patients with LAM was conducted by questionnaire. Survival probability was estimated using the Kaplan-Meier method, and the prognostic factors were analysed by Cox regression. Results: Data were collected on 173 patients with pulmonary LAM. The major presenting features were pneumothorax (43%) and exertional dyspnoea (37%). The survival probabilities for patients presenting with exertional dyspnoea (Group A) were 85%, 60% and 47% after 5, 10 and 15 years, respectively, and for patients presenting with pneumothorax (Group B) were 95%, 89% and 89%, respectively. Although the age at symptom onset was higher among patients in Group A than in Group B, Cox regression revealed that the presenting feature was a prognostic factor independent of age at symptom onset (Group A/B hazard ratio = 5.732, P < 0.01). In the subgroup of patients whose initial FEV1 was > 1000 mL, or FEV1/FVC > 40%, or %DLCO > 40%, the rate of deterioration in these tests was greater in Group A than in Group B (P < 0.01 for FEV1, P < 0.05 for FEV1/FVC and %DLCO). Conclusions: There are two possible subgroups of LAM patients. One subgroup that presented with pneumothorax, had onset of symptoms at a younger age and a more favourable prognosis; the other presented with exertional dyspnoea, had onset of symptoms at an older age and a poorer prognosis.