- •Muscle ultrasound in three children with SMA type 1 showed progressive atrophy and increased echogenicity over time.
- •Proximal muscles atrophied more than distal muscles.
- •Muscle ultrasound can appear normal in very young children with SMA type 1.
- •Quantitative muscle ultrasound may be a useful biomarker in SMA type 1.
Muscles are small in spinal muscular atrophy (SMA). It is not known if muscle size changes over time in SMA type 1. We quantified changes over time in muscle size and echointensity during two repeated ultrasound examinations of unilateral proximal (biceps brachii/brachialis and quadriceps) and distal (anterior forearm flexors and tibialis anterior) muscles in three children with SMA type 1. We compared muscle thickness (MT) to body weight-dependent normal reference values. Children were 1, 6, and 11 months old at baseline and had 2, 2 and 4 months between ultrasound examinations, respectively. At baseline, MT was normal for weight in all muscles except an atrophic quadriceps in the oldest child. MT decreased and echointensity increased (worsened) over time. At follow up, MT was below normal for weight in the quadriceps in all three children, in the biceps/brachioradialis in two, and in the anterior forearm in one. Tibialis anterior MT remained normal for weight in all three children. Muscle echointensity increased over time in all muscles and, on average, more than doubled in two children. In children with SMA type 1, muscle atrophies and becomes hyperechoic over time. Quantitative muscle ultrasound measures disease progression in SMA type 1 that warrants additional study in more children.
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Published online: August 26, 2015
Accepted: August 25, 2015
Received in revised form: August 10, 2015
Received: June 30, 2015
© 2015 Published by Elsevier Inc.