Selective neuropathy and preserved vascular responses in the diabetic Charcot foot

Abstract

Charcot arthropathy is a disabling complication of diabetic neuropathy. It is however, unclear why it occurs in only a small number of neuropathic patients. We have studied 12 diabetic patients (10 insulin-dependent) with an acute Charcot arthropathy, and compared their neuropathy and vascular responsiveness with 12 diabetic patients (10 insulin-dependent) with recurrent neuropathic foot ulceration, 12 diabetic control subjects (9 insulin-dependent) and 10 normal non-diabetic subjects. The Charcot arthropathy patients demonstrated a preservation of warm perception, 6 (5.5) °C, but complete loss of peripheral cold perception, 10 (0) °C, p <0.001 (median (interquartile range)). This contrasted with the ulcerated neuropathy patients, who had equally severe impairment of both warm and cold sensory thresholds, 10 (0.5) °C vs 10 (1) °C, respectively, the diabetic control subjects who were able to detect a 2 (1.3) °C warm stimulus and 3 (3.5) °C cold stimulus and the normal subjects, whose warm threshold was 2 (1) °C and cold was 2 (1) °C. Light touch perception at the foot was preserved in the Charcot patients 4 (4) g vs 100 (50) g, p <0.0002, in the ulcerated neuropathy patients. Vibration perception at the great toe and cardiovascular autonomic function tests (heart rate variability, Valsalva ratio and postural systolic blood pressure fall) were abnormal in both the Charcot patients and ulcerated neuropathy group, with no differences seen between the two groups. Peak skin blood flow at the great toe in response to local heating was preserved in the Charcot arthropathy patients, 63.36 (28.72) flow units when compared to the diabetic and normal subjects, 62.72 (47) flow units and 76.3 (33.92) flow units, respectively and much greater than in the ulcerated neuropathy patients 28.94 (37.39) flow units, p <0.0002. The diabetic patients developing Charcot arthropathy thus have a neuropathy and vascular responsiveness which distinguishes them from diabetic subjects developing neuropathic ulceration. This may be important in the pathogenesis of the Charcot foot.