• Rare lung diseases
• Exercise

Sporadic lymphangioleiomyomatosis (LAM) is a rare lung disease that affects almost exclusively women. It is characterised by cyst formation leading to airflow limitation, ventilatory limitations and gas exchange impairment, resulting in dyspnoea and exercise intolerance.1 Daily physical activity is an important clinical outcome parameter in common lung diseases, such as COPD.2 However, rare lung diseases such as LAM have not been studied so far and a disease-specific contribution to daily physical activity beyond airflow limitation is uncertain. In LAM, fatigue is a highly prevalent feature that has been overlooked in the past3 and that might be associated with levels of daily physical activity in this debilitating disease, just like health status and dyspnoea. Here, we hypothesised that physical activity in patients with LAM is substantially lower than in healthy controls but comparable with patients with COPD. In addition, we hypothesised that clinical variables other than airflow limitation and hypoxaemia might be associated with physical activity in patients with LAM.

We measured physical activity in 34 female patients with LAM, 32 female patients with COPD and 15 healthy women for 1 week using an activity monitor (SenseWear Armband; BodyMedia, Pittsburgh, USA) measuring steps per day (SPD), physical activity level (PAL) and minutes of at least moderate activity per day (MMA), as previously described.2 We recruited patients with LAM (mean age 52.7 years, mean FEV₁ 62.6% predicted, long-term oxygen therapy (LTOT): n=12 (35%)) during the annual meeting of the German LAM patient group. Patients with COPD (mean age 65.2 years, mean FEV₁ 62.7% predicted, LTOT: n=6 (19%)) were derived from an existing cohort4 and matched for FEV₁ and body mass index (BMI). Dyspnoea and health status were similar between groups. Healthy controls were recruited from our institutional database5 and matched for age and BMI (see online supplementary table E1 for detailed characteristics). All participants provided written informed consent (ethics approval AZ 038/12 II/AZ 185/08; German Clinical Trials Register Number DRKS00006170). Lung function parameters of patients with LAM were taken from the last available lung function report. Participants filled out questionnaires for generic and respiratory health status (12-Item Short Form Survey, SF-12; St. George's Respiratory Questionnaire, SGRQ), dyspnoea (modified Medical Research Council dyspnoea scale, mMRC) and fatigue (Multidimensional Fatigue Inventory, MFI-206) at home and sent them back together with the activity monitors at the end of the measurement.

Compared with healthy controls, each of the three physical activity parameters (SPD, PAL and MMA) was significantly reduced in patients with LAM (figure 1). Unadjusted comparison between patients with LAM and COPD showed reduced MMA in LAM (figure 1), despite the significant age difference and equal dyspnoea and health status scores. Adjusted for age and LTOT as possible confounders, multivariate regression analyses showed significantly lower MMA and PAL in patients with LAM compared with COPD (p=0.006 and p=0.005, respectively), whereas SPD were not significantly lower (p=0.152) (online supplementary table E2). A potential explanation for this observation might be that patients with LAM walk at lower intensities compared with patients with COPD.

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Figure 1

Physical activity of patients with lymphangioleiomyomatosis (LAM) (bright bar) compared with patients with COPD (light grey) and healthy controls (dark grey) expressed as mean±SE. (A) Number of steps per day (5852±3327 vs 6616±3351 vs 8863±1884; reduction by 12% vs 34%; p=0.360 and p=0.002, respectively). (B) Daily physical activity level (1.45±0.21 vs 1.54±0.26 vs 1.66±0.22; reduction by 24% vs 32%; p=0.087 and p=0.002, respectively). (C) Log transformed minutes of at least moderate activity per day (corresponding medians (IQR) were 61 (26–147) vs 107 (46–78) vs 153 (97–207); reduction of the median by 43% vs 60%; p=0.032 and p=0.006, respectively).

Airflow limitation, health status, dyspnoea and fatigue scores correlated best with SPD as outcome variable (online supplementary table E3). In multivariate regression analyses, adjusting for LTOT and FEV₁, either SF-12 physical health or MFI-20 were the strongest independent predictors for SPD in patients with LAM (total R²=0.476, partial R²=0.178, p=0.006 and total R²=0.449, partial R²=0.207, p=0.004, respectively) (online supplementary table E4).

Measures on exercise capacity (eg, 6 min walking test) and associated hypoxaemia might explain further variance in the data. The lack of these measurements is a clear limitation of our study.

We show for the first time that physical activity in daily life is substantially reduced in LAM patients, when compared with healthy controls and COPD patients with similar functional limitation, dyspnoea and health status—indicating a disease-specific impact. The underlying processes, however, are to be elucidated in further studies. Although airflow limitation and hypoxaemia—as indicated by FEV₁ and LTOT—are well-established predictors for impaired physical activity, we propose to include fatigue and generic health status into the standard clinical assessment of patients with LAM. Awareness and measurement of both features will help to improve adequate disease management in this debilitating disease.