Summation and CRPS?
MAJID SALEEM, MD; AHMED H. GHALEB, MD; CARMELITA S. PABLO, MD.
DEPT. OF ANESTHESIOLOGY, UNIV. OF ARKANSAS FOR MEDICAL SCIENCES
LITTLE ROCK, ARKANSAS

INTRODUCTION: Complex Regional Pain Syndromes (CRPS) I and II are significant health problems in US with high rate of treatment failure. The pathophysiology and natural course of CPRS remains obscure and management contentious. We report a case of ankle repair with history of CRPS I, in which we successfully prevented recurrence of CRPS.
CASE REPORT: Patient is a 32 year-old healthy male with trauma to right lower extremity developed CRPS I which was successfully treated over six months. He was scheduled for right pilon non-union. A popliteal fossa block was done with 0.25% levobupivacaine with bicarbonate and epinephrine in the preoperative area. A subarachnoid block was done in the operating room at L3-L4 interspace in sitting position using 1.2ml of 0.75% bupivicaine, 10 mcg fentanyl and 0.3 mg of morphine. A T10 level sensory level was achieved. Pt tolerated the surgery well and remained pain free asymptomatic.
DISCUSSION: The features of CRPS type I include an initiating noxious event or immobilization, allodynia or hyperalgesia with pain disproportionate to any inciting event, presence of edema, vasomotor and sudomotor changes. CRPS II shares the same symptomatology of CRPS I but follows an injury to a peripheral nerve. In CRPS I, the role of sympathetic blocks in diagnosis have been minimized. Studies suggest a 4–10% recurrence of CRPS after the first event.
Central nociceptive system can under go summation as a consequence of nociceptive afferent barrage. Temporal summation occurs when repetition of a stimulus increases pain perception and results in a short-lasting spinal cord sensitization. Spatial summation occurs when a nonpainful stimulus is perceived as painful when applied to a wider area and mechanisms are poorly understood. Repeated stimulation increases the excitability of spinal cord neurons, which persists after discontinuing the peripheral stimulation. This phenomenon is called "wind-up" and has an important role in acute and chronic pain
syndromes. Epidural anesthesia does not inhibit temporal summation because single stimuli, although not perceived as painful, arrive at the spinal cord and undergo summation and eventually evoke pain. In contrast, intrathecal anesthesia blocks the sensory input, thus completely inhibits the temporal summation and pain after repeated electrical stimulation. Spatial summation of nociceptive stimulation can occur during regional block. The only proven de-afferentation of nociceptive stimuli occurs with spinal anesthesia.
We effectively prevented the recurrence of CRPS I by placing popliteal fossa block and subarachnoid block and successfully inhibited the temporal summation and wind-up phenomenon.
CONCLUSION: The effectiveness of regional analgesia depends on the intensity and type of the stimulus applied. Because of the importance of summation mechanisms, hyperalgesia and allodynia in clinical pain, a greater use of methods that explore these mechanisms is desirable. Ultimately, the treatment goal is pain relief, functional recovery, and psychological improvement.
REFFERENCES:

1. SN Raja et al. CRPS I. Anesthesiology 2002; 96.
2. M Curatolo et al. Sensory assessment of regional analgesia in humans.
   Anesthesiology 2000; 93.

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