Diagnostic value of muscle MRI in differentiating LGMD2I from other LGMDs

Mutations in the fukutin-related protein (FKRP) have recently been demonstrated to cause limb girdle muscular dystrophy type 21 (LGMD21), one of the most common forms of the autosomal recessive LGMDs in Europe. We performed a systematic clinical and muscle MRI assessment in 6 LGMD21 patients and compared these findings with those of 14 patients with genetically confirmed diagnosis of other forms of autosomal recessive LGMDs or dystrophinopathies. All LGMD21 patients had a characteristic clinical phenotype with predominant weakness of hip flexion and adduction, knee flexion and ankle dorsiflexion. These findings were also mirrored on MRI of the lower extremities which demonstrated marked signal changes in the adductor muscles, the posterior thigh and posterior calf muscles. This characteristic clinical and MRI phenotype was also seen in LGMD2A. However, in LGMD2A there was a selective involvement of the medial gastrocnemius and soleus muscle in the lower legs which was not seen in LGMD21. The pattern in LGMD2A and LGMD21 were clearly different from the one seen in alpha-sarcoglycanopathy and dystrophinopathy type Becker which showed marked signal abnormalities in the anterior thigh muscles. Our results indicate that muscular MRI is a powerful tool for differentiating LGMD21 from other forms of autosomal recessive LGMDs and dystrophinopathies.