Diaphragm Weakness and Sleep-Related Breathing Disorders in Patients with Idiopathic Inflammatory Myopathy

Idiopathic inflammatory myopathies (IIMs) can cause respiratory muscle weakness, leading to diaphragm weakness (DW) and sleep-related breathing disorders (SRBD). We aimed to investigate clinical findings of DW and SRBD in patients with IIMs.

In patients with biopsy-confirmed IIMs, demographics, respiratory symptoms, single-breath counting (SBC), arterial blood gas, upright/supine SpO2 and spirometry, diffusing capacity for carbon monoxide (DLCO), maximal inspiratory and expiratory pressure (MIP, MEP), peak cough flow (PCF), and polysomnography parameters were prospectively evaluated. Epworth Sleepiness Scale (ESS), STOP-BANG, and Mallampati scores were recorded. The presence of at least one of two findings was considered suggestive of DW: (1) paradoxical abdominal movement (PAM), (2) upright-supine forced vital capacity (FVC) difference of ≥20%.

Sixteen patients (12 female/4 male, mean age: 54.4 ± 11.2/y, 9 dermatomyositis [DM], 6 polymyositis [PM], 1 inclusion body myositis [IBM]) were evaluated. Findings consistent with DW were observed in 25% of patients, and all of them had DM. MIP, MEP, and PCF were reduced in the majority of patients. Supine FVC% and supine SpO2 were significantly lower in patients with DW (P = .001 and P = .003, respectively). PaO2, SaO2, SBC, and PCF were lower, and the upright-supine SpO₂ difference was greater in patients with DW, although these differences were not statistically significant. Polysomnography was performed in 68.8% (n = 11) of patients. All 11 patients who underwent polysomnography had obstructive sleep apnea (OSA) (2 severe, 4 moderate, 5 mild).

Findings suggestive of DW were observed in 25% of patients with IIM and exclusively in those with DM, while OSA was identified in all patients who underwent polysomnography. These findings may support the clinical evaluation of both diaphragm involvement and sleep-related breathing disorders in patients with IIM.