Histopathological correlations and fat replacement imaging patterns in recessive limb-girdle muscular dystrophy type...

Area of Science:

• Neurology
• Radiology
• Pathology

Background:

• Limb-girdle muscular dystrophy autosomal recessive type 12 (LGMDR12) affects muscles selectively.
• The relationship between MRI proton density fat fraction (PDFF) and muscle biopsy findings in LGMDR12 is not well understood.
• The spatial distribution of fat replacement in LGMDR12 is unknown.

Purpose of the Study:

• To correlate MRI PDFF measurements with histopathological fat percentage in LGMDR12 muscle biopsies.
• To assess the spatial distribution of fat replacement in thigh muscles of LGMDR12 patients.
• To validate MRI PDFF as an outcome measure for LGMDR12.

Main Methods:

• 27 LGMDR12 patients and 27 controls underwent whole-body MRI and thigh 6-point Dixon imaging.
• 16 patients and 15 controls had muscle biopsies from semimembranosus, vastus lateralis, and rectus femoris.
• PDFF from MRI was correlated with biopsy fat percentage and the Rochester histopathology grading scale.

Main Results:

• Strong correlations were found between MRI PDFF and biopsy fat percentage in semimembranosus (r=0.85) and vastus lateralis (r=0.68) muscles.
• Similar correlations were observed between PDFF and the Rochester scale.
• Significantly inhomogeneous proximo-distal fat replacement was observed in all thigh muscles of LGMDR12 patients.

Conclusions:

• MRI PDFF measurements strongly correlate with muscle biopsy fat percentage in LGMDR12.
• Dixon fat fraction imaging is validated as a reliable outcome measure for LGMDR12.
• The inhomogeneous fat distribution highlights the importance of assessing entire muscles, not just samples, for clinical trials.