Abstract

OBJECTIVE—To characterize structural changes and the metabolic profile of foot muscles and correlate them with diabetic neuropathy measurements using phosphorus-31 (³¹P) rapid acquisition with relaxation enhancement (RARE) magnetic resonance imaging (MRI).

RESEARCH DESIGN AND METHODS—We studied 12 control subjects, 9 nonneuropathic diabetic patients, and 12 neuropathic diabetic patients using ³¹P RARE and proton (¹H) MRI at 3 Tesla. The ratio of the total cross-sectional area of the foot to that of the muscle tissue was calculated from transaxial ¹H and ³¹P images. The average ³¹P concentration across the metatarsal head region was measured from the ³¹P images.

RESULTS—The muscle area−to−total area ratio differed among all three groups (means ± SD): 0.55 ± 0.04 vs. 0.44 ± 0.05 vs. 0.06 ± 0.06 for control, nonneuropathic, and neuropathic subjects, respectively (P < 0.0001). The average ³¹P concentration also differed among all groups: 27.7 ± 3.8 vs. 21.7 ± 4.8 vs. 7.9 ± 8.8 mmol/l for control, nonneuropathic, and neuropathic subjects (P < 0.0001). The muscle area−to−total area ratio strongly correlated with clinical measurements: Neuropathy Disability Score, r = −0.83, P < 0.0001; vibration perception threshold, r = −0.79, P < 0.0001; and Semmes-Weinstein monofilaments, r = −0.87, P < 0.0001.

CONCLUSIONS—Small muscle atrophy is present in diabetes before clinical peripheral neuropathy can be detected using standard clinical techniques. The ³¹P RARE MRI method evaluates the severity of muscle atrophy, even in the early stages when neuropathy is absent. This technique may prove to be a useful diagnostic tool in identifying early-stage diabetic foot problems.