Phonatory assessments in patients with slowly progressive neuromuscular disorders: a new tool for evaluating...

Neuromuscular diseases (NMD) are a group of pathologies that affect the functionality of skeletal muscles and one of the main causes of morbidity and mortality in these patients is respiratory failure secondary to inspiratory muscle dysfunction. The diagnosis of inspiratory muscle dysfunction requires a combination of vital capacity (VC), maximum inspiratory pressure (MIP) and sniff nasal inspiratory pressure (SNIP). To assess whether it is possible using 3 techniques of peak phonation time (MPT) measurement to define lung function (VC < 50%ref) and inspiratory muscle dysfunction (MIP <80 cm H₂O or SNIP < 60 cm H₂O in women and < 70 cm H₂O in men) in patients with MND.

All patients with NMD who underwent pulmonary and respiratory muscle function assessment between June 2020 and May 2024 were selected. Vital capacity (VC), maximal inspiratory pressure (MIP), and sniff nasal inspiratory pressure (SNIP) were measured, in addition to evaluating MPT through A-time, Chrono Phonation Time (CPT), and Maximum Phonation Number (MPN).

Included were 92 patients with slowly progressive NMD (43 women), age 61 ± 14 years; diagnoses were myasthenia gravis (28.7%), myotonic dystrophy (22.8%), Facioscapulohumeral muscular dystrophy (19.6%). A-time, CPT and MPN correlated positively and statistically significantly with VC. Only A-time correlated positively and statistically significantly with MIP. A-time and MPN correlated positively and statistically significantly with SNIP. A-time ≤ 13 s predicted VC < 50%ref and inspiratory muscle dysfunction (sensitivity 59%-specificity 79%). CPT ≤ 15 s, predicts VC < 50%ref and inspiratory muscle dysfunction (sensitivity 52%-specificity 73%). MPN ≤ 18 s, predicts VC < 50%ref and inspiratory muscle dysfunction (sensitivity 56%-specificity 77%).

A-time, CPT and MPN all have values that allow defining the worsening of pulmonary capacity and inspiratory muscle function, which in turn, indicate the need for home mechanical ventilation in patients with slowly progressive MND.