Ultrasound May Help Assess Diaphragm Dysfunction in LOPD Patients

Ultrasound could help evaluate diaphragm and respiratory function in people with late-onset Pompe disease (LOPD), a study suggests.

The study, “Ultrasound assessment of diaphragm function in patients with late-onset Pompe disease,” was published in the journal Neurological Sciences.

LOPD is a genetic disorder caused by mutations in the GAA gene, which provides instructions for making an enzyme called acid alpha-glucosidase (GAA) that is responsible for the breakdown of a sugar molecule called glycogen.

Without this enzyme, glycogen starts accumulating inside cells until it reaches toxic levels, impairing certain organs and systems, especially the muscles. As a result, many LOPD patients develop progressive muscle weakness.

The diaphragm — the dome-shaped muscle that allows the chest to move with each breath — is often the most affected muscle in LOPD patients, and its dysfunction can lead to serious problems with respiratory function.

Diaphragm ultrasonography (DUS), or ultrasound, “is a relatively recent, easy to perform and reproducible technique that was utilized to evaluate diaphragm dysfunction in several respiratory diseases,” the researchers wrote.

However, few studies have investigated the usefulness of DUS in evaluating diaphragm dysfunction in patients with neuromuscular disorders.

To assess if DUS could be used for this purpose in LOPD patients, researchers at Università di Messina in Italy conducted a study in which they performed DUS to assess the thickness and mobility of the diaphragm in individuals with and without LOPD.

In addition, they also evaluated respiratory function by spirometry tests and muscle strength.

A total of 17 LOPD patients, at an average age of 47, and 17 healthy individuals used as controls participated in the study.

Results revealed worse lung function and higher muscle weakness in LOPD patients than in controls. In fact, patients had significantly lower values of forced vital capacity (FVC) in a seated and supine position, maximum inspiratory and expiratory pressure (MIP and MEP), thickness at functional residual capacity (FRC), and total lung capacity (TLC).

FVC measures the total amount of air a patient is able to exhale after taking a deep breath. MIP measures the strength of muscles used to inhale air and MEP to exhale air. Thickness at FRC measures the thickness of the diaphragm when a patient exhales, and TLC assesses the maximum amount of air found in the chest.

Further analyses found that a lower diaphragm thickness at FRC correlated with a lower MIP and seated FVC, while less diaphragm thickness at TLC was associated with decreased MIP and FVC, both seated and supine.

Investigators also found that less diaphragm thickness at FRC was linked to longer disease duration in LOPD patients, and that lower diaphragm mobility correlated with less thickness at TLC and FRC, as well as with decreased MIP and FVC, seated and supine.

“In conclusion, we suggested that DUS should become a routine method to evaluate diaphragm dysfunction in LOPD patients. Interestingly, DUS could help physicians in anticipating diagnosis of subclinical dysfunction of the diaphragm in LOPD patients,” the researchers wrote.

“If these data are confirmed in further clinical trials, DUS could be part of the diagnostic pathway in LOPD patients for the management of respiratory failure, including indication for noninvasive ventilation as well as a useful out-come measure for future diagnostic and therapeutic trials,” they added.