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Seventy-two patients suffering from chronic pain were treated with high frequency transcutaneous electrical nerve stimulation (hi-TNS). Significant predictors for a positive result were pains of neurogenic origin and pains located mainly in the extremities. CSF endorphin levels were determined for 22 patients with organic pain and the group with positive results from the treatment had somewhat (but not significantly) lower levels of fraction I endorphins. Age, sex or reported severity of pain had no predictive value.
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Johansson et al. (1980) studied this question.
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