This study aims to investigate the relationship between ultrasonographic muscle thickness measurement and echogenicity assessment with functional scales in children with spinal muscular atrophy (SMA). By utilizing ultrasonographic techniques, the study seeks to provide objective biomarkers for assessing muscle health and monitoring treatment response. Currently, the evaluation of SMA often relies on subjective clinical assessments; this study addresses that gap by offering more precise and objective indicators of disease progression and functional status. The ultimate goal is to improve treatment strategies and enhance patient outcomes through better assessment tools.

Spinal muscular atrophy (SMA) is a neuromuscular disorder that typically leads to progressive lower motor neuron loss from early childhood. The most common form is caused by deletions in the survival motor neuron 1 (SMN1) gene, inherited in an autosomal recessive manner. SMA is classified into at least three subtypes based on the age of onset and the level of motor development achieved. In Type 1 SMA (severe form), symptoms usually appear before 6 months of age, and children are unable to sit unsupported. In Type 2 SMA (intermediate form), symptoms start between 6 and 18 months, and children cannot walk unsupported. Type 3 SMA (mild form) presents after the second year of life, and affected children can walk unsupported. Although the exact prevalence and carrier rates of SMA in our country are not fully determined, it is estimated that there are between 130 and 180 new cases annually, given approximately 1,200,000 live births each year. The total number of SMA patients in the country is about 3,000.

Despite current treatments, muscle weakness and significant functional loss affecting quality of life are commonly observed in SMA patients. At present, the efficacy of SMA treatment is measured through clinical assessment, including monitoring of changes in motor developmental milestones and functional scales. However, the lack of objective biomarkers that are less reliant on patient cooperation, as opposed to functional scales, complicates monitoring treatment response for patients. Establishing reliable methods to assess disease progression and treatment response is crucial for conducting robust clinical studies.

Musculoskeletal ultrasonography presents itself as a suitable imaging modality for use as a biomarker in SMA management due to its non-invasiveness, repeatability, absence of radiation, ability to evaluate multiple muscles quickly, and ease of application. Furthermore, the feasibility of performing ultrasonographic examinations at the bedside facilitates access to a larger number of patients, especially those with limited mobility or requiring respiratory support. Previous literature has reported the advantages of muscle ultrasonography in evaluating neuromuscular disorders, including SMA.

In conclusion, this study, which will investigate the relationship between ultrasonographic muscle thickness measurement and echogenicity evaluation and functional scales in patients diagnosed with SMA for the first time in our country, will guide physicians and researchers seeking to assess disease progression, determine treatment efficacy, and develop rehabilitation strategies.

Inclusion Criteria:

• Age between 0-18 years
• Confirmed diagnosis of SMA through genetic testing
• Having received four loading doses of nusinersen
• Written consent provided for participation in the study

Exclusion Criteria:

• History of surgical operation or trauma in the muscles to be examined
• Presence of spasticity that complicates positioning of the extremities and hinders ultrasound imaging

Patients diagnosed with spinal muscular atrophy (SMA) who are being followed at the Department of Pediatric Neurology and the Department of Physical Medicine and Rehabilitation at Cerrahpaşa Medical Faculty