Pattern of pareses in 5q-spinal muscular atrophy

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Background: This prospective study investigates the pattern of pareses in 5q-associated spinal muscular atrophy (SMA) to identify disease-specific characteristics and potential differences from amyotrophic lateral sclerosis (ALS) and spinobulbar muscular atrophy (SBMA). Detailed knowledge about pareses patterns in SMA facilitates differential diagnosis and supports therapeutic monitoring. Methods: Between January 2021, and June 2021, 66 SMA patients (59.1% male, aged 33.6 ± 15.2 years) were included in the study. Most patients had SMA type II ( n = 28) or SMA type III ( n = 28), seven patients had SMA type I, and three patients had SMA type IV. We analyzed the pattern of pareses using the UK Medical Research Council (MRC) scoring system. Results: In both, upper and lower limbs muscle weakness was less pronounced in distal (upper limbs: MRC median 3.0 (interquartile range 1.5–3.5); lower limbs: 1.5 (0.5–3.0)) compared to proximal muscle groups (upper limbs: 2.0 (1.5–2.6); p < 0.001; lower limbs: 0.5 (0.5–1.5); p < 0.001). Thenar muscles were stronger than other small hand muscles (3.0 (2.0–3.5) vs 3.0 (1.5–3.5); p = 0.004). Muscles had more strength in upper (2.3 (1.5–3.1)) compared to lower limbs (1.1 (0.5–2.3); p < 0.001) and in flexors compared to extensors. Conclusion: We identified a specific pattern of muscle paresis in SMA which is different from the pattern of paresis in ALS and SBMA. As a rule of thumb, the pattern of pareses is similar, but not identical to ALS in distal, but different in proximal muscle groups.

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