Among male children with Duchenne muscular dystrophy (DMD), increased motor skills near the age of their expected peak suggest they’ll reach an older age before they lose their ability to stand and walk, according to study results published recently in Developmental Medicine & Child Neurology.

For children born with DMD who never received corticosteroid treatment, progressive weakening of muscles, lung, and heart function advancing to loss of ambulation (LOA) occurs by age 10. However, patients who have received long-term treatment with corticosteroids will experience LOA about 2 to 4 years later. The North Star Ambulatory Assessment (NSAA) shows healthy male functional abilities peak at 4 years of age and those with DMD typically between 6 and 7 years of age.

The objective of the current study was to evaluate the association between functional test scores (NSAA and the timed rise from floor [TRF]) recorded at peak age for male children with DMD, and the age of those children at LOA.


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The researchers conducted a retrospective study of 293 male patients with DMD enrolled in the UK North Star Network database from 13 centers with a NSAA score taken between 6 years and 7 years 6 months of age, at least one visit older than 8 years of age, and follow-up beyond 3 years. At baseline (6 years 10 months±6 months) the median highest NSAA score was 27 (IQR: 22-31) and the mean TRF was 4.9 seconds (±2.9). Corticosteroid use data at baseline was available for 224 patients. An additional 30 patients had never been treated with steroids though 23 of those patients subsequently received corticosteroid treatment.

For the entire cohort (first visit at 5 years 6 months±1 year 2 months; last visit 12 years 8 months±2 years 11 months; median follow-up 7 years 4 months) a higher baseline NSAA and lower baseline TRF associated with an older age at LOA (P <.001). NSAA scores of 32 to 34 had a probability of 0.61 vs scores of 26 to 31 with probability of 0.34 to remain ambulant beyond 13 years of age. Of the 293 patients in the study, 160 lost ambulation (estimated median age at LOA 11 years 8 months [IQR: 10 years 1 month – 14 years 5 months]). Researchers noted, “In multivariable analysis, NSAA, TRF, and corticosteroid daily regimen (vs intermittent) were all independently associated with outcome (P =.01).”

Study limitations included: missing data in the NSAA database, large percentage of patients switching steroid type or regimen, and looking at data from a single country standard of care.

Researchers concluded, “both NSAA and TRF recorded at the age of expected peak are significant determinants of age at LOA in male children with DMD, the latter being more important even when recorded early in the disease course.” This could be helpful knowledge for early-stage family counseling concerning prognosis.

Reference

Zambon AA, Ayyar Gupta V, Ridout D, et al. Peak functional ability and age at loss of ambulation in Duchenne muscular dystrophy. Dev Med Child Neurol. Published online February 14, 2022. doi:10.1111/dmcn.15176



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