Objective:

Background: Early-onset Friedreich’s Ataxia (FA) concerns a classic pediatric phenotype (p-FA, starting before 18 years of age), characterized by relentlessly progressive ataxia and (cardio)myopathy. Delayed-onset FA (d-FA, starting after 25 years of age) is characterized as a rarer phenotype with mild myopathy and clear neuropathic involvement. Until now, neuromuscular data about the intermediate FA group (i-FA, starting between 18 and 25 years of age) are incomplete. Therefore, we aimed to compare quantitative muscle ultrasound parameters between p-FA and i-FA phenotypes.

Methods: In patients with p-FA [n=8; median assessment age 14 (range 12-41) years], i-FA [n=7; median assessment age 42 (34-53) years] and age-matched healthy controls, we compared visual and quantitative muscle ultrasound density (MUD of proximal (quadriceps) and distal (tibialis-anterior) leg muscles).

Results: Visual muscle ultrasound assessment could discriminate between i-FA and controls (77% correctly identified) but not between p-FA and i-FA phenotypes (50% correctly identified). MUD outcomes of tibialis-anterior and quadriceps muscles discriminated between i-FA phenotypes and controls (both p< 0.03), but not between p-FA and i-FA phenotypes (neither individual MUD outcomes, nor quantitative proximal to distal MUD ratio’s).

Conclusions: Visual and quantitative MUD leg-muscle parameters are substantially higher in i-FA than in controls, but do not discriminate between p-FA and i-FA phenotypes. These findings may implicate that pediatric and intermediate FA onset phenotypes may concern the same neuromuscular phenotype. Future comparative MUD assessment in d-FA phenotypes may hopefully indicate whether the neuromuscular phenotype differs between pediatric & intermediate versus delayed phenotypes, or not.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/muscle-ultrasound-comparison-between-early-and-intermediate-onset-friedreichs-ataxia/