Delays in Diagnosing SMA, Especially Type 3, Still Evident, Study Finds

Delays in diagnosing spinal muscular atrophy are still evident, particularly for those with SMA type 3, despite recent changes in recommendations for disease detection and care, a study from Italy reports.

Such delays are particularly relevant as targeted therapies are now available, and growing evidence links greatest benefit to early treatment.

The study, “Diagnostic journey in Spinal Muscular Atrophy: Is it still an odyssey?,” was published in the journal PLOS One.

A genetic neurodegenerative disorder, SMA is characterized by the gradual loss of motor neurons — nerve cells responsible for controlling voluntary muscles — in the spinal cord, and by progressive muscular weakness. It is divided into subtypes (ranging from type 0 to type 4) depending on age at disease onset and symptom severity.

The diagnosis process is thought to be relatively straightforward, as most SMA patients show a typical constellation of symptoms, including generalized weakness and loss of muscle tone (hypotonia) that is more severe in the arms and legs and does not affect the face.

Physicians also have genetic tests at their disposal for SMA, which are relatively easy to perform nowadays.

“Despite the typical clinical features and the ease in performing the genetic analysis, a recent review of the diagnostic process in SMA reports that this is not always so straightforward and that there is often a delay between the onset of clinical signs and confirmed diagnosis in all types of SMA,” the researchers wrote.

An early diagnosis of SMA is crucial both for genetic counseling and to guide treatment, which should be initiated as soon as possible to ensure better outcomes.

Researchers in Italy set out to determine the age at diagnosis in SMA subtypes manifesting early in life, as well as the time lag between the identification of clinical signs and a confirmed genetic diagnosis.

They reviewed data covering 480 children with a confirmed SMA diagnosis — 191 with type 1, 210 with type 2, and 79 with type 3 — who were being followed at five tertiary, or specialized, centers in Italy.

Parameters analyzed included age at disease onset, age at diagnosis, the time interval between onset and a definitive diagnosis, and the type of tests conducted to achieve a final diagnosis.

In infants with SMA type 1, the mean age of disease onset was 2.75 months, and the mean age of diagnosis was 4.70 months; this means that, on average, these children had a diagnosis delay of nearly two (1.94) months.

With relatively milder SMA types — those with type 2 and 3 disease — the time interval between outward signs and definitive diagnosis tended to lengthen.

In children with type 2, the mean age of disease onset was 10.0 months, and for diagnosis 15.6 months; on average, these children remained undiagnosed for more than five months.

For those with type 3, the mean age of disease onset was 32.0 months (about 2.66 years), and the mean age of diagnosis was 4.34 years. On average, almost 1.5 years passed since these children received a final diagnosis.

In all three groups, disease symptoms were most often first recognized by parents — 62.83% of all type 1 cases, and 74.76% and 84.81%, respectively, among types 2 and 3 cases — than by a pediatrician or other health-related professional.

More than half of the children with SMA type 1 (67.02%) and type 2 (56.19%) had genetic tests as a sole diagnostic tool.

This was also the case for many of those with SMA type 3 (40%), but a higher proportion of type 3 children first underwent tests that included electromyography (EMG), brain magnetic resonance imaging (MRI), and muscle biopsies.

“A possible explanation [for the delay in type 3 patients] is that with decreasing severity, the clinical signs are milder and can be less specific, as also proven by the highest number of investigations such as brain MRI and EMG, performed more often in type 3, and progressively less in type 2 and type 1,” the researchers wrote.

“Our results suggest that despite improved care recommendations there is still a marked diagnostic delay, especially in type 3,” they concluded. “At the time new therapies are becoming available more attention should be devoted to reducing such delay as there is consistent evidence of the benefit of early treatment.”