Pressure pain perception in the diabetic Charcot foot: facts and hypotheses.

Background: Reduced traumatic and posttraumatic (nociceptive) pain is a key feature of diabetic neuropathy. Underlying condition is a gradual degeneration of endings of pain nerves (A-delta fibers and C-fibers), which operate as receivers of noxious stimuli (nociceptors). Hence, the absence of A-delta fiber mediated sharp pain ("first" pain), and of C-fiber mediated dull pain ("second" pain). However, patients with diabetic neuropathy and acute Charcot foot often experience deep dull aching in the Charcot foot while walking on it.

Aim: To create a unifying hypothesis on the kind of pain in an acute Charcot foot.

Result: Absence of punctuate (pinprick) pain perception at the sole of a Charcot foot, as was shown recently, likely corresponds to vanished intraepidermal A-delta fiber endings. C-fiber nociceptors are reduced, according to histopathology studies. Both types of fibers contribute to posttraumatic hyperalgesia at the skin level, as studies show. Their deficiencies likely impact on posttraumatic hyperalgesia at the skin level and, probably, also at the skeletal level.

Conclusion: It is hypothesised that deep dull aching in an acute diabetic Charcot foot may represent faulty posttraumatic hyperalgesia involving cutaneous and skeletal tissues.