Magnetic resonance imaging techniques demonstrate soft tissue damage in the diabetic foot

Aims. Our objective was to assess the qualitative soft tissue changes which occur in the diabetic neuropathic foot, which may predispose to ulceration , using a specific magnetic resonance imaging (MRI) contrast sequence, magn etization transfer (MT) which produces contrast based on exchange between w ater bound to macromolecules (e.g. collagen) and free water (e.g. extracell ular fluid). Methods. The first metatarsal head of Ig diabetic neuropathic subjects and 11 diabetic non-neuropathic controls was studied using a 'targeted' radiofr equency coil. Neuropathy was classified using vibration perception threshol d (VPT) (< or > 25 V), cold threshold (< 1 degrees C or > 4 degrees C) and Michigan neuropathy score (< 5 or > 15). Peripheral vascular disease was ex cluded. Results were expressed as percentage of tissue MT activity in a cro ss-sectional area. At autopsy full thickness biopsies were taken from the p lantar fat pad of Io unrelated subjects with diabetic neuropathy. Results. Healthy muscle displays high MT activity, whereas adipose tissue i nduces little activity. Muscle MT activity was considerably reduced (75 +/- 20%, 30 +/- 24%, P < 0.001) and fat pad MT activity was considerably incre ased in subjects with neuropathy (37 +/- 17% 68 +/- 21%, P< 0.001). Muscle fibre atrophy decreases MT activity, whereas fibrous infiltration of the fa t pad increases MT activity, fibro-atrophic post-mortem histological change s were found in the plantar fat pads of all neuropathic subjects examined ( n = 10). Conclusions. Changes in MT activity reflect qualitative structural changes which this study reveals are extensive in the diabetic neuropathic foot. Fi brotic atrophy of the plantar fat pad may affect its ability to dissipate t he increased weight-bearing forces associated with diabetic neuropathy.