Early changes in the skin microcirculation and muscle metabolism of the diabetic foot

Background Changes in the large vessels and microcirculation of the diabetic foot are important in the development of foot ulceration and subsequent failure to heal existing ulcers. We investigated whether oxygen delivery and muscle metabolism of the lower extremity were factors in diabetic foot disease. Methods We studied 108 patients (21 control individuals who did not have diabetes, 36 patients with diabetes who did not have neuropathy, and 51 patients with both diabetes and neuropathy). We used medical hyperspectral imaging (MHSI) to investigate the haemoglobin saturation (SHSIO2; % of oxyhaemoglobin in total haemoglobin [the sum of oxyhaemoglobin and deoxyhaemoglobin]) in the forearm and foot; we also used P-31-MRI scans to study the cellular metabolism of the foot muscles by measuring the concentrations of inorganic phosphate and phosphocreatine and calculating the ratio of inorganic phosphate to phosphocreatine (Pi/PCr). Findings The forearm SHSIO2 during resting was different in all three groups, with the highest value in controls (mean 42 [SD 17]), followed by the non-neuropathic (32 [8]) and neuropathic (28 [8]) groups (p<0.0001). In the foot at resting, SHSIO2 was higher in the control (38 [22]) and non-neuropathic groups (37 [12]) than in the neuropathic group (30 [12]; p=0.027). The Pi/PCr ratio was higher in the non-neuropathic (0.41 [0.10]) and neuropathic groups (0.58 [0.26]) than in controls (0.20 [0.06]; p<0.0001). Interpretation Our results indicate that tissue SHSIO2 is reduced in the skin of patients with diabetes, and that this impairment is accentuated in the presence of neuropathy in the diabetic foot. Additionally, energy reserves of the foot muscles are reduced in the presence of diabetes, suggesting that microcirculation could be a major reason for this difference.