Untreated complex regional pain syndrome (CRPS) may progress from acute stages with increased hair and nail growth in the affected limb to chronic stages with atrophy of the skin, muscles and bones. The aim of this study was to investigate whether tissue hypoxia could be one mechanism responsible for this late CRPS symptoms. Nineteen patients with CRPS and two control groups (healthy control subjects, surgery patients with edema) participated in this study. Skin capillary hemoglobin oxygenation (HbO(2)) was measured non-invasively employing micro-lightguide spectrophotometry (EMPHO). The EMPHO probe was mounted force-controlled onto the skin of the affected and unaffected hand. HbO(2) was measured at rest and during postischemic reactive hyperemia. HbO(2) did not differ between the right (58.20%+/-1.12) and left (57.79%+/-1.31, ns) hand in control subjects. However, in patients, HbO(2) of the affected side (36.63%+/-2.16) was significantly decreased as compared to the clinically unaffected side (46.35%+/-2.97, P<0.01). As compared to controls, HbO(2) in CRPS was reduced on both sides (P<0.001). Postischemic hyperoxygenation was impaired on the affected side in CRPS (60.81%+/-2.90)--as compared to the unaffected side (67.73%+/-1.50, P<0.04) and to controls (68.63%+/-0.87, P<0.005). The unaffected limb in CRPS did not differ from controls. Despite skin edema, pre- (49.06%+/-2.02) and postsurgery HbO(2) (53.15%+/-4.44, ns) were not different in the second control group. Our results indicate skin hypoxia in CRPS. Impairment of nutritive blood flow in the affected limb may be one factor contributing to atrophy and ulceration in chronic CRPS. The investigation of patients after surgery revealed that edema could not be the only reason for hypoxia.

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Context: Past evidence has shown that invasive and non-invasive brain stimulation may be effective for relieving central pain.Objective: To perform a topical review of the literature on brain neurostimulation techniques in patients with chronic neuropathic pain due to traumatic spinal cord injury (SCI) and to assess the current evidence for their therapeutic efficacy. Methods: A MEDLINE search was performed using following terms: "Spinal cord injury", "Neuropathic pain", "Brain stimulation", "Deep brain stimulation" (DBS), "Motor cortex stimulation" (MCS), "Transcranial magnetic stimulation" (TMS), "Transcranial direct current stimulation" (tDCS), "Cranial electrotherapy stimulation" (CES). Results: Invasive neurostimulation therapies, in particular DBS and epidural MCS, have shown promise as treatments for neuropathic and phantom limb pain. However, the long-term efficacy of DBS is low, while MCS has a relatively higher potential with lesser complications that DBS. Among the non-invasive techniques, there is accumulating evidence that repetitive TMS can produce analgesic effects in healthy subjects undergoing laboratory-induced pain and in chronic pain conditions of various etiologies, at least partially and transiently. Another very safe technique of non-invasive brain stimulation -tDCS -applied over the sensorymotor cortex has been reported to decrease pain sensation and increase pain threshold in healthy subjects. CES has also proved to be effective in managing some types of pain, including neuropathic pain in subjects with SCI. Conclusion: A number of studies have begun to use non-invasive neuromodulatory techniques therapeutically to relieve neuropathic pain and phantom phenomena in patients with SCI. However, further studies are warranted to corroborate the early findings and confirm different targets and stimulation paradigms. The utility of these protocols in combination with pharmacological approaches should also be explored.

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