Nusinersen Improves Respiratory Muscle Strength in Patients With SMA Type 2

Study results are boosting the case for using nusinersen in patients with spinal muscular atrophy (SMA) Type 2, revealing that the treatment improves the strength of external intercostal muscles performance compared with historical controls.

These improvements, which researchers note in Pediatric Pulmonology show the treatment increases the strength of the main respiratory muscles involved in the disease, were seen after 6 injections of nusinersen.

The small group of 16 patients showed improvements across 3 tools of measurement: maximal static inspiratory pressure (MIP), forced vital capacity (FVC), and esophageal pressure (Pes) during a maximal sniff.

“Respiratory muscle involvement in SMA is characterized by a predominant weakness of the intercostal and abdominal muscles with a relative spared diaphragm,” wrote the researchers. “Our results are thus particularly interesting by showing an improvement in respiratory muscle tests which assesses these muscles, such as the [maximal sniff esophageal pressure (sniff Pes)] and MIP, but also a tendency for improvement in the expiratory muscle strength tests, such as [gastric pressure] cough and [maximal expiratory pressures].”

Data from 12 patients were collected for inspiratory muscle strength assessed based on sniff Pes and MIP, showing that outcomes were significantly better among these patients than the 14 historical controls. According to the researchers, there was a trend for a better MIP percent predicted, and FVC—an indirect indicator of inspiratory and expiratory muscle strength—also markedly improved.

Meanwhile, the effect on the diaphragm was less pronounced, with researchers observing a nonsignificant improvement in maximal sniff transdiaphragmatic pressure Pdi and for expiratory muscle strength. According to the researchers, the latter finding, coupled with improved sniff Pes, may suggest that “nusinersen is associated with an improvement in the strength of the accessory inspiratory muscles which may be able to counteract the negative pleural pressure swings developed by the diaphragm.”

The group’s findings are in line with data from another group that evaluated the respiratory muscle function during quiet breathing in 27 infants with SMA Type 1, the authors say.

They also took a look at the impact on motor function, finding that this marker also significantly improved, which is consistent with previous studies. In month 14, following injection 6, Hammersmith Infant Neurologic Examination Part 2 scores had dropped by more than 2 points in 7 patients. Total Motor Function Measure test scores also significantly improved.

“Our results underline the usefulness of an age‐adapted respiratory muscle assessment as endpoint for innovative treatments in SMA,” the authors concluded. “Motor function also significantly improved, as observed in other studies, in SMA 1c and 2 treated with nusinersen.”

Reference

Banda M, Amaddeo A, Khirani S, et al. Assessment of respiratory muscles and motor function in children with SMA treated by nusinersen. Pediatr Pulmonol. Published online October 29, 2020. doi:10.1002/ppul.25142