Cough efficacy is related to the disability status in patients with multiple sclerosis

Cough is an important defense mechanism, whose main function is to remove mucus and/or foreign bodies from the airways. In patients with multiple sclerosis (MS), respiratory muscle function may be affected and cough may be impaired.

Respiratory muscle strength and voluntary cough efficacy were determined in MS patients and controls, and the relationship between cough efficacy and patients' degree of disability was investigated.

We recruited 27 MS patients (age: 41 +/- 11 years; 18 females) with mild-to-moderate disability, Expanded Disability Status Scale (EDSS) score range: 1-7, and 20 healthy controls (age: 37 +/- 11 years; 12 females). The maximal inspiratory (PIMAX) and expiratory (PEMAX) pressures, maximal whistle mouth pressures (PMOW), cough peak flows (CPF), cough expiratory volumes (CEV) and cough gastric pressures (PGA) were measured in all subjects.

In MS patients, the EDSS score was significantly related to CPF, PEMAX, PMOW, cough PGA, PIMAX and CEV (p < 0.01, each correlation). The receiver-operating characteristic curve showed that an EDSS score > or =5.5 was consistent with impaired cough (CPF < or =5.6 l/s), with a sensitivity of 0.85 and a specificity of 0.95 (area under curve 0.90, p < 0.001). CPF was related to and predicted by PEMAX, PMOW, cough PGA and PIMAX in MS patients (p < 0.01 each correlation), but not in controls.

MS can affect voluntary cough efficacy and respiratory muscle strength, which are inversely related to the patients' degree of disability. In addition, this study shows that CPF is a measure of clinical relevance in MS patients.