I read about this in the Medscape newsletter, but can’t access the journal Neurology to review it. The American Academy of Neurology has issued a practice guideline/ evidence-based review (link to the information release here) recommending that TENS not be use for chronic LBP, but should be considered for pain from diabetic polyneuropathy.
I can’t read the study so I can’t comment, but the Medscape article did mention that an absence of evidence is not evidence of absence, referring to an editorial that is in the same issue as the systematic review (I can’t copy or link to the Medscape article either due to copyright) and noting that meta-analyses are limited by the quality and quantity of trials. The guideline calls for further trials and makes specific recommendations for them.
The editorial did state that “this updated evidence-based review is valuable in providing the limits of our evidence base… Nevertheless, it is not unreasonable to take a practical position that, in spite of the relatively weak scientific and clinical evidence, TENS still represents a valuable therapeutic alternative in neurologic pain disorders.”