American Journal of Roentgenology, Vol 161, 347-351, Copyright © 1993 by American Roentgen Ray Society
MR imaging as a potential diagnostic test for metabolic myopathies: importance of variations in the T2 of muscle with exercise
P Jehenson, A Leroy-Willig, E de Kerviler, D Duboc and A Syrota
Service Hospitalier Frederic Joliot, CEA, Orsay, France.
OBJECTIVE. Most metabolic myopathies (like glycogenoses and mitochondrial
myopathies) are related to inborn errors of muscle energy metabolism and
often present clinically as exercise intolerance (inability to sustain
normal exercise). We investigated whether the previously observed absence
of normal exercise-induced variation in the T2 of muscle in McArdle's
disease (a metabolic myopathy caused by muscle phosphorylase deficiency)
was specific for this disease and whether the variations in T2 could be
used for screening patients suspected of having metabolic myopathy.
SUBJECTS AND METHODS. Exercise- induced variations in proton MR signal and
in intracellular pH were studied in the forearm flexor muscles of nine
healthy subjects and 49 patients with exercise intolerance due to muscle
pain, suggesting a metabolic myopathy. The relative increase in T2, delta
T2/T2, was measured from MR spin-echo images before and after exercise.
Phosphocreatine (used as a control of the degree of exercise) and
intracellular pH were measured from phosphorus-31 spectra before and during
exercise. The progressive 4.5-min handgrip exercise reached maximal
exertion capability at the end of exercise and decreased phosphocreatine to
less than 50% of its rest value. RESULTS. Variations in T2 and end-exercise
pH were correlated. The nine healthy subjects showed a delta T2/T2 ranging
from +19% to +44% (but little T1 variation). Ten patients with McArdle's
disease showed only slight delta T2/T2 (0-10%). There was no overlap with
values for healthy subjects, but there was some with values for other
patients. Of the 21 subjects with a delta T2/T2 less than 19%, 19 had a
metabolic myopathy. The other two had a congenital neuromuscular disorder
(one central core disease, one nemaline myopathy) with type I fiber
predominance (type I muscle fibers are characterized by a high oxidative
metabolism and a low lactic acid production). CONCLUSION. The altered
increase in T2 was sensitive but not specific for McArdle's disease.
However, as variations in T2 reflect variations in pH, they seem to be
specific for myopathies in which there is little exercise-induced decrease
in pH (some metabolic myopathies and congenital neuromuscular disorders
with type I fiber predominance) among patients in whom exercise intolerance
is the main symptom. Our results suggest that MR imaging might be useful as
a screening test for these diseases.
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