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In children with Friedreich ataxia, muscle and ataxia parameters are associated
Deborah A Sival1, Maria E Pouwels, Agnes Van Brederode
1Department of Paediatrics, University Medical Center Groningen, University of Groningen, the Netherlands. d.a.sival@bkk.umcg.nl
Insights
In children with Friedreich ataxia (FRDA), muscle weakness significantly influences International Cooperative Ataxia Rating Scale (ICARS) scores. This suggests ICARS may not accurately reflect true ataxia progression in FRDA patients.
Area of Science:
- Neurology
- Pediatrics
- Genetics
Background:
- Friedreich ataxia (FRDA) is a rare inherited disease causing progressive nervous system damage.
- The International Cooperative Ataxia Rating Scale (ICARS) is commonly used to assess ataxia severity in FRDA.
- Muscle weakness is a known symptom of FRDA, but its impact on ICARS scores is not fully understood.
Purpose of the Study:
- To investigate whether muscle weakness confounds ICARS scores in pediatric patients with Friedreich ataxia.
- To determine the relationship between muscle parameters and ataxia assessments in children with FRDA.
Main Methods:
- A study involving 12 children with FRDA and 12 age-matched controls.
- Muscle ultrasound density (MUD), muscle force, and sensory evoked potentials were measured.
- Association between muscle parameters and ICARS scores was analyzed.
Main Results:
- Children with FRDA exhibited increased muscle ultrasound density, particularly in proximal leg muscles.
- Muscle weakness was more pronounced in proximal than distal muscles and in legs compared to arms.
- ICARS leg subscores correlated with leg muscle force in FRDA patients, especially when sensory function was absent.
Conclusions:
- ICARS scores in children with FRDA are significantly confounded by underlying muscle weakness.
- Relying solely on ICARS for longitudinal evaluation may not accurately reflect ataxia progression in FRDA.
- Further research is needed to refine ataxia assessment tools in FRDA.
Aim:
In children with Friedreich ataxia (FRDA), ataxia is assessed using the surrogate marker the International Cooperative Ataxia Rating Scale (ICARS). We aimed to determine whether ICARS scores in children with FRDA are confounded by muscle weakness.
Method:
In 12 children with FRDA (10 males, two females; mean age 13 y 6 mo, SD 2 y 6 mo) and 12 age-matched children without FRDA (nine males; three females), we determined the association between muscle and ataxia parameters (i.e. muscle ultrasound density (MUD), muscle force, sensory evoked potentials, and ICARS scores). Children with FRDA were included on the basis of FXN gene analysis. Children in the comparison group were included on basis of uneventful pregnancy and normal cognitive and neurological development.
Results:
In children with FRDA, muscle ultrasound density was homogeneously increased in the biceps, quadriceps, and tibialis anterior muscles (median 4SD). FRDA muscle weakness was significantly more pronounced in proximal than in distal muscles (-2SD vs -0.5SD respectively; p=0.004), with a stronger impairment of leg muscles than of arm muscles (-2SD vs -0. SD respectively; p=0.001). Comparing MUD between children with FRDA and an age-matched comparison group revealed a relatively strong increase in MUD in the proximal leg muscles in the FRDA group. Under the condition of persistently absent sensory evoked potentials, leg ICARS subscores in the FRDA group appeared to be positively associated with leg muscle force until a maximal plateau level of ICARS subscores was reached.
Interpretation:
In children with FRDA, ataxia scales based on ICARS are confounded by muscle weakness. Longitudinal ICARS evaluations in children with FRDA do not necessarily indicate altered ataxia.
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