Introduction: FOP is a severely disabling ultra-rare genetic disorder. Mean survival is only 40-50 years as a result of cardiopulmonary complications due to progressive immobilizing heterotopic ossification of the chest cavity. While spirometry is a known metric of disease severity, the forced expiratory maneuvers are difficult in this population. Osc is a different lung function test that is performed during normal breathing and highly sensitive to changes in respiratory mechanics.
Objective: To characterize Osc in FOP patients.
Methods: 4 patients with FOP were recruited for Osc prior to PFT. Cumulative analogue joint involvement scale (CAJIS) scores are used to evaluate total body and regional FOP burden.
Results: Of 4 FOP patients (mean age=29.8 years; 1M,3F), 1 had thoraco-lumbar spine CAJIS score of 1 (out of 2) and 3 had score of 2. We observed lower X5 (reactance at 5Hz) in patients with higher CAJIS score (-3.10 vs -1.23 cmH2O.s/L) with tidal changes between inspiration and expiration (?X5/X5.in) of 32-35% that are higher than healthy controls (12%). This is likely reflective of increased stiffness of the lung and chest wall tissues, indicating thoracic involvement and associated chest wall rigidity.
Conclusions: Osc provides additional information about disease severity regarding airway and thoracic involvement to help track disease progression and response to potential therapies in FOP patients.
Table 1.
| CAJIS score 1 (n=1) | CAJIS score 2 (n=3) | Healthy controls (n=65) | |
| X5 | -1.23 | -3.10 | -1.18 |
| X5.in | -1.51 | -3.71 | -1.06 |
| X5.ex | -1.03 | -2.48 | -0.94 |
| ?X5/X5.in, % | 31.69 | 35.23 | 11.68 |
| %FVC | 60.50 | 50.57 | 95.04 |
| %FEV1 | 64.30 | 57.83 | 92.24 |
ex, during expiration; in, during inspiration.