[Muscular exercise intolerance syndrome in Becker muscular dystrophy]

To determine whether exertional muscle pain syndrome (EMP) is a benign phenotype or an early stage of Becker-type muscular dystrophy (BMD).

Muscle dystrophin analysis led to the diagnosis of BMD in 6 patients complaining of EMP.

Three patients had a history of X-linked inheritance and age at clinical onset was 4 to 11 years in five, and one patient had a later onset aged 23. Pseudohypertrophy of the calf muscles was absent in one patient, but all had experienced mild (5/6) pelvic weakness and (or) atrophy one to 17 years after the onset. High serum CK level was present (X 14). Normal anti-dystrophin immunostaining in two cases did not rule out the diagnosis that was only made made by Western blot analysis or genetic studies. All exhibited in-frame deletions (exons 45-48) within the dystrophin gene.

The 36 patients with BMD-EMP analysed in the literature, exhibited different deletions and no worsening in 66.7% of cases. Western blot was more precise than immunolabelling with 96.8% positivity versus 70.5%. Dystrophin analysis by Western blot and (or) DNA analysis should be included in the evaluation of patients with EMP syndrome without deficient muscle energy metabolism, particularly those with pseudohypertrophy of the calf muscles or high serum CK levels.