Motor and Cognitive Delay in Duchenne Muscular Dystrophy: Implication for Early Diagnosis

Objectives: To examine the relationship between delay in the age of first independent walking and cognitive impairment in boys with Duchenne muscular dystrophy (DMD) to assess how age of diagnosis might be improved.

Study Design: We reviewed the records of 179 boys with DMD evaluated by the senior author between 1989 and June 2012. Delay in walking was defined as occurring at or greater than 16 months of age. Cognitive impairment was identified by school placement in special education or lower than expected grade level during the elementary school years.

Results: Delay in walking and cognitive impairment are highly correlated (P ≤ .0001). If cognitively delayed, boys with DMD were 3 times more likely to have a delay in walking. This association was shown to be independent from the rate of motor degeneration (P = .9) and the age of diagnosis (P = .6, combined average = 5.1 ± 2 years).

Conclusion: Delay in the onset of walking in boys with DMD is strongly associated with cognitive delay. We suspect that primary care givers overlook DMD as a possible cause of delay in the age of independent walking when early features of cognitive delay are also apparent. DMD should be included among those disorders causing global developmental delay. Recognition of this association could substantially decrease the age of diagnosis for many boys with DMD. We suggest that the standard evaluation for boys with global developmental delay include an inexpensive and sensitive serum creatine kinase test.