Abnormal and collateral innervations of sympathetic and peripheral sensory fields associated with a case of causalgia

A 41-year-old female developed spontaneous burning pain (causalgia) and stimulus-induced dysesthesia (allodynia) of the dorso-lateral part of her right foot following trauma. An L3 and L4 sympathectomy eliminated the spontaneous burning pain for only 1 year, but did not affect the stimulus-induced dysesthesia. We evaluated her two years post-sympathectomy with grouped sequential anesthetic blocks and sensory testing. Sympathetic blocks at L1 and L2 eliminated the burning pain and normalized heat perception from baseline hyperalgesia, indicating that the causalgia had been reactivated via more rostral sympathetic ganglia. Anesthetic block of the sural nerve eliminated both the burning pain and the stimulus-induced dysesthesia. During the sural nerve block, perception of touch and pin, but not heat, was preserved in the sural distribution. All perception was lost following subsequent block of the peroneal branches. When the peroneals were blocked first, perception of touch, pin and heat remained in the sural distribution. With peroneal block the burning pain was eliminated, but the stimulus-induced dysesthesia remained, even in the anesthetic peroneal territory. When sural block was added to the peroneal block the stimulus-induced dysesthesia was eliminated, and sensation in the sural distribution was lost. We conclude that the sural distribution received overalapping innervation for touch and pin-prick perception, but that heat perception, burning pain and the stimulus-induced dysesthesia were sural nerve dependent. Further, we were able to dissociate causalgia pain from allodynia in this patient.