What are the key clinical features to consider when diagnosing Spinal Muscular Atrophy (SMA) in children?

The key clinical features to consider when diagnosing Spinal Muscular Atrophy (SMA) in children primarily involve progressive muscle weakness and hypotonia [Adam et al., 1993]. These symptoms arise from the degeneration of anterior horn cells in the spinal cord [Adam et al., 1993].

General signs that should prompt consideration of a neurological condition, including SMA, in children include unexplained progressive weakness, persistent hypotonia, or developmental delay affecting motor milestones NICE NG127. Persistent or worsening motor difficulties, changes in muscle tone, or unusual movements also warrant further investigation and specialist referral NICE NG127.

Specific features vary by SMA type. For instance, children with Spinal Muscular Atrophy Type 2 typically experience symptom onset between 6 and 18 months of age [Cancès et al., 2020]. These children can usually sit independently but are unable to stand or walk without support [Cancès et al., 2020]. The weakness is often progressive and more pronounced in the legs than the arms [Cancès et al., 2020]. A common clinical sign in SMA Type 2 is a fine tremor of the hands, known as polyminimyoclonus [Cancès et al., 2020]. Other complications that may be observed due to muscle weakness include scoliosis and joint contractures [Cancès et al., 2020]. Respiratory muscle weakness can also lead to recurrent respiratory infections and restrictive lung disease [Cancès et al., 2020]. Across SMA types, deep tendon reflexes are typically absent or reduced, and intellectual development is usually normal [Adam et al., 1993]. Tongue fasciculations may also be present, particularly in more severe forms [Adam et al., 1993].