To the editor:

We were surprised to read the title, abstract and conclusions of a recent article in Nature Medicine by Freund et al.: “Nogo-A specific antibody treatment enhances sprouting and functional recovery after cervical lesion in adult primates” (ref. 1), as no clear anatomical evidence of regeneration is provided in the paper.

The authors performed spinal cord lesions on monkeys, then quantified the “normalized cumulated axonal length” beyond the lesion in six monkeys, three treated with Nogo-A antibody and three with control. In the text, the authors report that the difference between the two groups “was not statistically significant (P = 0.12),” a conclusion that can be verified directly from the specific values reported in Supplementary Table 1 of ref. 1 (48.8 μm, 36.7 μm and 8 μm of regeneration for controls, compared to 59.3 μm, 46 μm and 79.9 μm in monkeys treated with Nogo-A antibody).

The authors do show a statistically significant increase in “the number of axonal swellings.” However, this parameter was not validated as a measure of regeneration. Swellings are just as likely to be signs of incipient degeneration as they are of any anatomical improvement. Unless evidence is provided to the contrary, these data cannot be taken as evidence of enhanced repair.

Finally, the authors refer in the text to Supplementary Figure 1 as showing “sprouting for a total distance of 10–12 mm,” but that figure does not in fact contain those data, nor could we find any data on the extent of sprouting in any of the other figures or tables, nor any indication of the statistical significance of this purported effect.

We were therefore surprised that the concluding paragraph states that “Neutralization of Nogo-A promotes regrowth of corticospinal (and possibly other) axons around the lesion and into the denervated spinal cord in macaque monkeys,” as the data on regrowth (that is, regeneration) showed no statistically significant difference. We were equally surprised that the title and abstract claim that the Nogo-A antibody produces “enhanced sprouting,” as sprouting was not documented.

Because the conclusions of the paper do not match the data that are presented, it would seem appropriate for the authors to revise their conclusions in an erratum.