Spontaneous breathing pattern in children with spinal muscle atrophy (SMA)

Abstract

SMA is an autosomal recessive disease characterized by degeneration of motor neurons of spinal cord resulting in muscle wasting and weakness with normal diaphragmatic activity and intercostal muscles impairment. The non-lethal most severe form is classified as type II while the mildest as type III. In adulthood the thoraco-abdominal pattern of breathing differs according to the forms of the disease, being similar between SMAII and wheelchair bounded SMAIII patients, while ambulant SMAIII patients almost behave like healthy controls (HC). In order to verify the hypothesis that respiratory differences are present since childhood, rapid and shallow breathing (RSB), tidal volume (V T ) and ribcage expansion (V RC ) were measured in 28 SMAII (median age: 3.9 yrs), 7 SMAIII (5.6 yrs) and 14 HC (5.2 yrs) children during quiet breathing in seated position by Opto-Electronic Plethysmography. SMAII children were characterized by higher RSB and reduced V T compared to SMAIII and HC. V T was lower because of impaired V RC . Conversely, a similar ventilatory pattern was found between SMAIII and HC (figure). In conclusion, intercostal muscles weakness starts since early childhood in SMAII leading to rapid and shallow breathing with poor thoracic expansion during quiet breathing. Early respiratory rehabilitation can be useful in SMAII to try to delay the consequence of intercostals weakness such as lung restriction and ineffective cough.