Diagnostic interest of whole-body MRI in early- and late-onset LAMA2 muscular dystrophies: a large international cohort

International audienceBackground LAMA2-related muscular dystrophy (LAMA2-RD) encompasses a group of recessive muscular dystrophiescaused by mutations in the LAMA2 gene, which codes for the alpha-2 chain of laminin-211 (merosin). Diagnosis is straightforward in the classic congenital presentation with no ambulation and complete merosin defciency in muscle biopsy, but isfar more difcult in milder ambulant individuals with partial merosin defciency.Objective To investigate the diagnostic utility of muscle imaging in LAMA2-RD using whole-body magnetic resonanceimaging (WBMRI).Results 27 patients (2–62 years, 21–80% with acquisition of walking ability and 6 never ambulant) were included in aninternational collaborative study. All carried two pathogenic mutations, mostly private missense changes. An intronic variant (c.909+7A>G) was identifed in all the Chilean cases. Three patients (two ambulant) showed intellectual disability,epilepsy, and brain structural abnormalities. WBMRI T1w sequences or T2 fat-saturated images (Dixon) revealed abnormalmuscle fat replacement predominantly in subscapularis, lumbar paraspinals, gluteus minimus and medius, posterior thigh(adductor magnus, biceps femoris, hamstrings) and soleus. This involvement pattern was consistent for both ambulant andnon-ambulant patients. The degree of replacement was predominantly correlated to the disease duration, rather than to theonset or the clinical severity. A “COL6-like sandwich sign” was observed in several muscles in ambulant adults, but diferentinvolvement of subscapularis, gluteus minimus, and medius changes allowed distinguishing LAMA2-RD from collagenopathies. The thigh muscles seem to be the best ones to assess disease progression.Conclusion WBMRI in LAMA2-RD shows a homogeneous pattern of brain and muscle imaging, representing a supportivediagnostic tool