Proton magnetic resonance spectroscopy of the intrinsic tongue muscles in patients with myasthenia gravis with different autoantibodies

Abstract

Objective To assess lipid composition of the intrinsic tongue muscles in patients with myasthenia gravis (MG). Methods This study included 15 MG patients with antibodies against muscle-specific kinase (MuSK), 15 matched MG patients with antibodies against acetylcholine receptor (AChR) and 15 matched healthy subjects. Middle posterior region of the tongue was analyzed by single voxel point-resolved proton magnetic resonance spectroscopy (MRS) using 1.5 T MRI scanner. Results MRS obtained from subject with AChR MG showed a broad resonance arising from methylene groups of lipids (PMN) with no observable shoulder attributed to methyl groups (PML). Full-width at half maximum (FWHM) of PMN + PML peak showed higher value in patients with AChR MG in comparison to healthy subjects and MuSK MG patients (p < 0.05). In patients with MuSK MG, the shape and FWHM of PMN + PML peak was similar as in healthy subjects (p > 0.05), with tendency toward increased ratio between PMN and resonance from vinyl protons of lipids (PV). In both AChR and MuSK MG, total creatine resonance (creatine + phosphocreatine, CP) was almost absent with significant increase of PMN/CP ratio in comparison to healthy subjects (p < 0.05). Conclusion MRS is useful in revealing muscle lipid composition in MG. In patients with AChR MG, MRS showed increased lipid content in the tongue muscles due to the lipid migration from intra- to extramyocellular space. Finding in patients with MuSK MG might reflect intramyocellular lipid deposition in the tongue. CP decrease in tongue muscles indicated impairment of oxidative metabolism in both AChR MG and MuSK MG.