A Retrospective Cohort Study of Idiopathic Diaphragmatic Palsy: a Diagnostic Triad, Natural History and Prognosis

Background: Isolated diaphragmatic palsy in the absence of progressive neuromuscular disease is uncommon. It poses diagnostic challenges and limited data are available regarding prognosis. We present retrospective cohort data from two large teaching hospitals in the United Kingdom.

Method: 60 patients who were assessed either as inpatients or outpatients were included in this study. Patients with progressive neuromuscular disease were excluded. Clinical presentation, tests of respiratory muscle function (sitting/supine vital capacity, maximal expiratory pressure (MEP), maximal inspiratory pressure (MIP) and sniff nasal inspiratory pressure (SNIP)) and outcomes were recorded.

Results: For patients with diaphragmatic palsy, mean±sd seated and supine vital capacity pre-noninvasive ventilation (NIV) were reduced at 1.7±1.2 L and 1.1±0.9 L, respectively, with a mean±sd postural fall in vital capacity of 42±0.16%. The mean MEP/MIP and MEP/SNIP ratios for diaphragmatic palsy were 3 and 3.5, respectively. After a year of treatment with NIV, mean±sd upright and supine vital capacity had increased to 2.1±0.9 L and 1.8±1 L, respectively, and the mean±sd fall in vital capacity from sitting to supine reduced to 29±0.17%. MEP/MIP and MEP/SNIP ratios reduced to 2.6 and 2.9, respectively, from the pre-NIV values. The values of postural fall in vital capacity correlated (p<0.05) with MEP/MIP and MEP/SNIP ratio (r=0.86 and r=0.7, respectively).

Conclusion: Tests of respiratory muscle strength are valuable in the diagnostic workup of patients with unexplained dyspnoea. A triad of 1) orthopnoea, with 2) normal lung imaging and 3) MEP/MIP and/or MEP/SNIP ratio ≥2.7 points towards isolated diaphragmatic palsy. This needs to be confirmed by prospective studies.