title: Muscle imaging data in late-onset Pompe disease reveal a correlation between the pre-existing degree of lipomatous muscle alterations and the efficacy of long-term enzyme replacement therapy.
abstract: BACKGROUND
  Late-onset Pompe disease (LOPD) is a metabolic myopathy caused by mutations in GAA and characterized by proximal muscle weakness and respiratory insufficiency. There is evidence from clinical studies that enzyme replacement therapy (ERT) with human recombinant alpha-glucosidase improves motor performance and respiratory function in LOPD.
  
  
  OBJECTIVE
  We analyzed quantitative muscle MRI data of lower limbs to evaluate the effects of long-term ERT on muscle parameters.
  
  
  METHODS
  Three symptomatic LOPD patients who received ERT for five years and four untreated presymptomatic LOPD patients were included in the study. T1-weighted MRI images were used to determine volumes of thigh and lower leg muscles. In addition, mean gray values of eight individual thigh muscles were calculated to assess the degree of lipomatous muscle alterations.
  
  
  RESULTS
  We detected a decrease in thigh muscle volume of 6.7% (p < 0.001) and an increase in lower leg muscle volume of 8.2% (p = 0.049) after five years of ERT. Analysis of individual thigh muscles revealed a positive correlation between the degree of lipomatous muscle alterations at baseline and the increase of gray values after five years of ERT (R(2) = 0.68, p < 0.001). Muscle imaging in presymptomatic patients showed in one case pronounced lipomatous alteration of the adductor magnus muscle and mild to moderate changes in further thigh muscles.
  
  
  CONCLUSIONS
  The results demonstrate that fatty muscle degeneration can occur before clinical manifestation of muscle weakness and suggest that mildly affected muscles may respond better to ERT treatment than severely involved muscles. If these findings can be validated by further studies, it should be discussed if muscle alterations detected by muscle MRI may be an objective sign of disease manifestation justifying an early start of ERT in clinically asymptomatic patients in order to improve the long-term outcome.
authors.affiliation: Department of Neurology, Heimer Institute for Muscle Research, University Hospital Bergmannsheil, Ruhr-University, Bochum, Germany.
authors.forename: Kai Michael
authors.initials: KM
authors.lastname: Gruhn
authors.affiliation: Institute of Radiology, University Hospital Bergmannsheil, Ruhr-University, Bochum, Germany.
authors.forename: Christoph Malte
authors.initials: CM
authors.lastname: Heyer
authors.affiliation: Department of Neurology, Heimer Institute for Muscle Research, University Hospital Bergmannsheil, Ruhr-University, Bochum, Germany.
authors.forename: Anne-Katrin
authors.initials: AK
authors.lastname: Güttsches
authors.affiliation: Department of Neurology, Heimer Institute for Muscle Research, University Hospital Bergmannsheil, Ruhr-University, Bochum, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Rehmann
authors.affiliation: Institute of Radiology, University Hospital Bergmannsheil, Ruhr-University, Bochum, Germany.
authors.forename: Volkmar
authors.initials: V
authors.lastname: Nicolas
authors.affiliation: Department of Neurology, Heimer Institute for Muscle Research, University Hospital Bergmannsheil, Ruhr-University, Bochum, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Schmidt-Wilcke
authors.affiliation: Department of Neurology, Heimer Institute for Muscle Research, University Hospital Bergmannsheil, Ruhr-University, Bochum, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Tegenthoff
authors.affiliation: Department of Neurology, Heimer Institute for Muscle Research, University Hospital Bergmannsheil, Ruhr-University, Bochum, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Vorgerd
authors.affiliation: Department of Neurology, Heimer Institute for Muscle Research, University Hospital Bergmannsheil, Ruhr-University, Bochum, Germany.
authors.forename: Rudolf Andre
authors.initials: RA
authors.lastname: Kley
keywords: ERT, enzyme replacement therapy; Enzyme replacement therapy; LOPD, late onset Pompe disease; MRI; MRI, magnetic resonance imaging; Muscle imaging; Muscle volume; Myopathy; Pompe disease; rhGAA, human recombinant alpha-glucosidase