The authors raise two important issues when dealing with the assessment of the autonomic nervous system: the definition of the completeness of sympathetic lesion and its relationship with the American Spinal Injury Association (ASIA) neurological examination.

Very few studies have focused on the completeness or incompleteness of the autonomic lesion in spinal cord injury (SCI) individuals. The sympathetic skin response (SSR) is, by far, the most used technique for this purpose: the presence of SSR below the lesion in response to a stimulus above the lesion is indicative of an incomplete sympathetic lesion.1, 2, 3, 4, 5 Apart from the SSR, a few studies have directly addressed this issue. In paraplegics, the lack of vasoconstriction in the calf during the hand cold pressor test, indicates a lack of supraspinal control of sympathetic outflow to the leg vasculature,6 whereas a positive pressor response to mental arithmetic and hand cutaneous cold along with the lack of postural hypotension confirm a functionally competent sympathetic outflow.7 In tetraplegics, the absence of vasoconstriction of the skin of the hand after a sudden loud noise, pin-pricks on the face and neck or ice applied to the same region is indicative of the completeness of the lesion.8

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