NEW TOOLS OF FUNCTIONAL EVALUATION OF PATIENTS WITH METABOLIC MYOPATHIES

Metabolic myopathies are an heterogeneous group of genetic diseases in which the defect is at the level of some enzymes responsible for the provision of energy for muscle contraction. The clinical picture may vary from a mild to a serious disease, in which the reduced exercise tolerance may significantly limit the patient’s quality of life. The reduced exercise tolerance needs to be quantified, by non-invasive, sensitive and precise tools, in order to be able to follow the clinical course of the disease, as well as to evaluate the effects of therapeutical and/or rehabilitation interventions. In the present Project we propose to evaluate, in patients with metabolic myopathies, two methods of functional evaluation of skeletal muscle oxidative metabolism (the system in which oxygen [O2] is utilized for energy provision), which were the object of a previous Telethon grant, dealing with studies conducted on animal models, healthy subjects and different types of patients. These methods are the study of the kinetics of adjustment of O2 uptake during the transition from rest to exercise (a faster kinetics indicates better conditions for skelatal muscle oxidative metabolism) and, in particular, the study of muscle oxygenation during exercise by near-infrared spectroscopy (NIRS). This method, completely non-invasive, is based on the administration to muscle, by means of a probe positioned on the skin, of light at some specific wavelengths. Analysis of the absorbed light at the various wavelengths allows to estimate muscle oxygenation, that is the relationship between O2 delivery to and O2 utilization by the tissue under investigation. If some preliminary data will be confirmed, NIRS could allow to identify and quantify a key pathophysiological aspect in these patients, that is the incapacity by muscle to increase O2 extraction from blood in order to sustain increased needs for energy provision.