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A 5 year old boy with motor retardation presented with proximal weakness maximal in the lower limbs and generalised muscular atrophy. The deep tendon reflexes were absent. Tremor or fasciculations were not seen. The muscles of the boy were examined by a high resolution ultrasound system and real time compound imaging. The deep muscles consisted of atrophic fibres (bright areas in fig 1) with groups of hypertrophic fibres (black areas in fig 2). The analysis of the survival motor neurone (SMN) 1 gene resulted in a homozygous deletion of exon 7 and 8 confirming the diagnosis of spinal muscular atrophy.
Muscle fibres of the denervated motor unit atrophy. Reinnervation by collateral sprouting results in grouping of hypertrophic fibres with the same histochemical type, commonly called “type grouping”.
Using this new ultrasound technique, ultrasound morphological findings can be compared to histological findings.
Competing interests: none declared