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

Background and objective: 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 1000 mL, or FEV 1 /FVC >40%, or %DL CO >40%, the rate of deterioration in these tests was greater in Group A than in Group B ( P < 0.01 for FEV 1 , P < 0.05 for FEV 1 /FVC and %DL CO ). 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.