D.P.20 CT volumetry demonstrates muscle volume decrement in GNE myopathy

Abstract

GNE myopathy, alternatively called distal myopathy with rimmed vacuoles or hereditary inclusion body myopathy, is caused by missense mutations in GNE gene. Efficacy of sialic acid supplementation therapy is demonstrated in model mice and now phase II clinical trial is planned. However, evaluation method for muscle status, including that for muscle volume, is not well established for GNE myopathy. We previously reported the net muscle volumetry, which estimated the muscle volume of middle part of thigh. To know whether the net muscle volumetry by CT that we previously reported can demonstrate the muscle volume decrement along the disease course in GNE myopathy. Nineteen patients with GNE myopathy were studied twice with 6-month interval. CT images of fourteen 1-cm thickness slices of mid-thigh between 7cm above and below midpoint of trochanter and patella, and of twenty 5-mm thickness slices of mid-lower leg between 5cm above and below midpoint of fibula head and lateral malleolus were analyzed. Muscle density map was obtained using estimated linear-function. Obvious vessels and skin tissues were excluded manually from the density map and net muscle volume of thighs and lower legs was calculated. In the patients whose muscle volume was less than 200cm3, the decrement of muscle volume was not constant, because most muscle was replaced by fat and connective tissue. In patients whose net muscle volume was more than 200cm3, the decrement of net muscle volume of thigh and leg was 6.32%/year and 8.14 %/year, respectively. The leg edema was observed in two patients, that made us difficult to distinguish muscle from edematous tissue in manual eliminating procedure, because CT value of muscle tissue was close to that of edematous tissue. The net muscle volume decrement can be measured by CT. This method may be useful to evaluate muscle status especially in clinical trial.