EMG STUDY IN THE DIAGNOSIS AND DIFFERENTIAL DIAGNOSIS OF LIPID STORAGE MYOPATHY

Clinical, electromyographic and pathological features were studied in 18 patients with lipid storage myopathy (group I ) and 18 patients with polymyositis and dermatomyositis (group II). The results showed a remarkable lower spontaneous activity(SA) incidence (14% ) in group I than that (55% ) in group II; 46% and 34% short-duration motor unit potentials (MUAPs) with polyphasic potentials and 74% and 71% short-duration MUAPs without polyphasic potentials respectively; the percentages of increased polyphasic MUAPs were same in the two groups. The reduced or pathologic interference patterns accounted for 61 % in the group I and 50% in group II. Increased CPK, LDH and HBD were also found in both of them. It is suggested that the lipid storage myopathy may be diagnosed when patients have muscle weakness and myalgia with short-duration and low-amplitude and polyphasic MUAPs without or with occasional spontaneous activities, and increased CPK, LDH and HBD.

Skeletal Muscle Magnetic Resonance Imaging of the Lower Limbs in Late-onset Lipid Storage Myopathy with Electron Transfer Flavoprotein Dehydrogenase Gene Mutations

Background： Lipid storage myopathy （LSM） is a genetically heterogeneous group with variable clinical phenotypes. Late-onset multiple acyl-coenzyme A dehydrogenation deficiency （MADD） is a rather common form of LSM in China. Diagnosis and clinical management of it remain challenging, especially without robust muscle biopsy result and genetic detection. As the noninvasion and convenience, muscle magnetic resonance imaging （MRI） is a helpful assistant, diagnostic tool for neuromuscular disorders. However, the disease-specific MRI patterns of muscle involved and its diagnostic value in late-onset MADD have not been systematic analyzed. Methods： We assessed the MRI pattern and fat infiltration degree of the lower limb muscles in 28 late-onset MADD patients, combined with detailed clinical features and gene spectrum. Fat infiltration degree of the thigh muscle was scored while that ofgluteus was described as obvious or not. Associated muscular atrophy was defined as obvious muscle bulk reduction. Results： The mean scores were significantly different among the anterior, medial, and posterior thigh muscle groups. The mean of fat infiltration scores on posterior thigh muscle group was significantly higher than either anterior or medial thigh muscle group （P 〈 0.00 l）. Moreover, the mean score on medial thigh muscle group was significantly higher than that of anterior thigh muscle group （P 〈 0.01）. About half of the patients displayed fat infiltration and atrophy in gluteus muscles. Of 28 patients, 12 exhibited atrophy in medial and/ or posterior thigh muscle groups, especially in posterior thigh muscle group. Muscle edema pattern was not found in all the patients. Conclusions： Late-onset MADD patients show a typical muscular imaging pattern of fat infiltration and atrophy on anterior, posterior, and medial thigh muscle groups, with major involvement of posterior thigh muscle group and gluteus muscles and a sparing involvement of anterior thigh compartment. Our findings also suggest that muscle MRI of lower limbs is a helpful tool in guiding clinical evaluation on late-onset MADD.

A novel PNPLA2 mutation causing total loss of RNA and protein expression in two NLSDM siblings with early onset but slowly progressive severe myopathy

Neutral lipid storage disease with myopathy(NLSDM)is a rare autosomal recessive disorder,due to an enzymatic error of lipid metabolism.Patients present always with skeletal muscle myopathy and variable cardiac and hepatic involvement.NLSDM is caused by mutations in the PNPLA2 gene,which encodes the adipose triglyceride lipase(ATGL).Here we report the molecular characterization and clinical findings of two NLSDM siblings carrying the novel c.187t1G>C homozygous PNPLA2 mutation,localized in the splice site of intron 2.Molecular analyses revealed that neither aberrant PNPLA2 mRNA isoforms,nor ATGL mutated protein were detectable in patient’s cells.Clinically,both patients presented early onset muscle weakness,in particular of proximal upper limb muscles.In almost 15 years,muscle damage affected also distal upper limbs.This is a NLSDM family,displaying a severe PNPLA2 mutation in two siblings with clinical presentation characterized by an early onset,but a slowly evolution of severe myopathy.