Pressure pain perception at the injured foot: the impact of diabetic neuropathy

At feet with painless diabetic neuropathy (PDN) and a healed fracture (quiescent Charcot-foot), cutaneous pressure pain perception threshold (CPPPT) is elevated beyond the range of measurement, whereas deep pressure pain perception threshold (DPPPT) may be normal. It is unknown, how these thresholds behave under the conditions of a foot injury. We therefore measured CPPPT and DPPPT in the vicinity of a unilateral active foot injury. 18 diabetic patients with PDN and plantar injury, partly involving the skeleton (Wagner grade I-II ulcer), 10 non-neuropathic subjects with acute painful skeletal injury (sprain, fracture) and 20 healthy control subjects without foot injury were studied. CPPPT was measured using calibrated monofilaments, and DPPPT was measured by Algometer II® over muscle and joint. Compared to control subjects, non-neuropathic acutely injured (and contralateral) feet displayed lowered CPPPT and DPPPT. Conversely, ulcerated and contralateral feet with PDN displayed unmeasurably elevated thresholds in 100% (CPPPT), 72% (DPPPT over joint), and 28% (DPPPT over muscle) of patients, respectively. In the vicinity of an active foot injury, physiologic hyperalgesia was demonstrated in the non-neuropathic subjects, but not in the patients with PDN in whom neglect of foot trauma is, therefore, common.