Magnetic Resonance Imaging, Vol. 14, No. 10, pp. 1137- 1141, 1996 Copyright 0 1996 Ekevier Science Inc. Printed in the USA. All rights reserved 0730-725X/96 $15.00 + .OO ELSEVIER l Original Contribution PI1 SO730-725X( 96) 00236-O MR QUANTIFICATION OF MUSCLE FATTY REPLACEMENT IN McARDLE’S DISEASE ERIC DE KERVILER,*? ANNE LEROY-WILLIG,? DENIS DUBOC,$$ BRUNO EYMARD,$\/ AND ANDI& SYROTA~ *Service de Radiologie, Hbpital Saint-Louis, 75010 Paris, France, iService Hospitalier Frederic Joliot, CEA, 91406 Orsay, France, $INSERM U153 and, §Service de Cardiologie, HGpital Cochin, 75014 Paris, France, \\Consultation de Pathologie Neuro-Musculaire, H&pita1 de la Salpetribre, 75013 Paris, France McArdle’s disease is an energy-dependant disorder of skeletal muscle caused by the inability to break down glycogen. The aim of this study was to quantify fatty replacement in patients with McArdle’s disease. Calf and thigh axial spin echo T1-weighted magnetic resonance (MR) images (repetition time 500 ms, echo time 25 ms) were obtained at 0.5 T in nine patients with McArdIe’s disease (age 51 + 16 years, range 26-74) and nine sex- and age-matched healthy subjects (age 52 ? 16 years, range 29-78) to quantify intramuscular fat. Regions of interest were drawn manually, encompassing the largest cross section of muscle. A fatty replacement index (IF) was determined from histograms of signal in the regions of interest in calf and thigh muscles. In normal subjects, IF = 3.6 2 2.8% in calf and 4.9 2 2.3% in thigh. In patients, IF = 11 rt 9.3% in calf and 13.5 2 10.4% in thigh, significantly different from IF values in normal subjects 0, = .03). IF correlated well with age in patients (p = .03). In older patients, up to 25% of the muscle volume was replaced by fat. Patients with McArdle’s disease, usually weakly disabled, exhibit significant muscle fatty replacement on MR images. These findings suggest a progressive muscle loss over time related to the disease process. Copyright 0 1996 Elsevier Science Inc. Keywords: Magnetic resonance imaging; Muscle diseases; Muscular glygogenoses; McArdle’s disease. INTRODUCTION McArdle’s disease, which belongs to the wide group of metabolic myopathies, is caused by the absence of myophosphorylase, one of the enzymes involved in glycogenolysis.’ This enzymatic defect is responsible for an inability to break down muscle glycogen and therefore to produce energy. The disease starts with easy fatigability of muscles, exercise intolerance, and intermittent myoglobinuria. Later in adult life, persis- tent weakness and muscle wasting develop. In many myopathies, a progressive replacement of muscle by fat has been shown using various imaging modalities.*-” Metabolic myopathies are much less disabling than muscular dystrophies, in which degener- ating fibers are replaced by connective and adipose tissue. Nevertheless, a few reports of muscle fatty re- placement in metabolic myopathies have been pub- lished.‘2s’3 Having also observed by clinical magnetic reso- nance (MR) examinations abnormal muscles in some patients with metabolic myopathies, we aimed to deter- mine whether MR imaging (MRI) was able to detect and quantify fatty replacement in calf and thigh mus- cles of patients with McArdle’s disease. MATERIALS AND METHODS Patients Nine patients with McArdle’s disease (seven men, two women, age 51 + 16 years, range 26-74) and nine age- and sex-matched healthy sedentary volun- teers (seven men, two women, age 52 + 16 years, range 29-78) were studied. The diagnosis of McAr- dle’s disease was ascertained by histochemical and bio- chemical assays on muscle biopsy samples for all pa- tients.14 The assays showed excessive muscle glycogen RECEIVED l/24/96; ACCEPTED 618196. tal Saint-Louis, 1 avenue Claude-Vellefaux, 75010 Paris, Address correspondence to Eric de kerviler, M.D., HGpi- France. 1137