Early Detection Emphasized Amidst Era of Changing Clinical Course of SMA

As the clinical course of spinal muscular atrophy (SMA) continues to evolve due to the emergence of novel therapies like nusinersen, researchers are offering guidance for primary care providers, who play a vital role in early suspicion and referral for the disease.

Coupled with these new interventions for treating SMA is an emphasis on diagnosing the disease as early as possible to ensure optimal clinical outcomes for patients. Both preclinical and clinical research has pointed to better treatment response and survival outcomes associated with early treatment initiation for the disease.

“SMA is now a treatable neurodegenerative disease, and early detection and treatment are crucial. As a result of the availability of novel, time-critical treatment options, GPs [general practitioners] are now playing a key part in the early recognition of this condition,” explained the researchers in Australian Journal of General Practice. “It is important that all GPs consider urgent referral for a child with delayed motor milestones and signs of symmetrical weakness.”

Delays in diagnosis are not uncommon for SMA, with some research pointing to gaps in diagnosis that range from a few months to more than 3 years. One systematic review has shown that time from the onset of SMA symptoms to a diagnosis was 3.6 months for SMA type 1 (children aged 0-6 months), 14.3 months for SMA type 2 (children aged 6-18 months), and 43.6 months for SMA type 3 (children older than 18 months to younger than 21 years).

The signs and symptoms of SMA could contribute to the delays in the disease’s diagnosis, as many of these manifestations also present with other neuromuscular conditions, including congenital myopathies, limb-girdle muscular dystrophies, and dermatomyositis.

“The classical clinical triad of SMA is muscle atrophy, fasciculations, and areflexia in a cognitively normal child,” the researchers wrote. “However, diagnosis can be delayed because subtle early signs may be difficult to detect. For example, as the individual with SMA transitions from presymptomatic to symptomatic, preserved or brisk tendon reflexes may be evident on examination and fasciculations may not yet be present.”

For children with SMA, the cornerstone of disease is progressive, predominantly proximal weakening of muscles, although the presentations of symptoms will vary based on the severity of disease and the child’s age. For example, younger infants (0-6 months; SMA type 1), who account for approximately 60% of SMA cases, tend to fail basic motor milestones such as head control and rolling because of the severe weakness that could lead to swallowing difficulties or growth failure. Pelvic girdle muscles are also affected. Other features include bright and alert face despite weakness elsewhere and paradoxical breathing pattern.

In infants older than 6 months and in children (SMA types 2 and 3), signs and symptoms tend to be more mild, contributing to the longer delay in diagnosis vs younger infants. Initially these children typically have normal motor trajectory before showing inabilities or delays in functions like walking or going up and down the stairs compared with their peers. Other signs and symptoms include hand tremors, absent deep tendon reflexes, and tongue fasciculations. Notably, they will rarely experience signs in their facial muscles and extraocular extremities.

Reference

Davidson J, Farrar M. The changing therapeutic landscape of spinal muscular atrophy. Aust J Gen Pract. 2022;51(1-2):38-42. doi:10.31128/AJGP-03-21-5924