A systematic review and meta-analysis of literature on greater occipital nerve block for the treatment of chronic migraine headaches published in Plastic and Reconstructive Surgery has extensive limitations and ultimately raises more questions than answers, according to a discussion article published in the same edition of the journal.
For their review and meta-analysis, researchers analyzed data pooled from 9 randomized controlled trials (RCTs), concluding that, when compared with placebo, greater occipital nerve blocks reduced both headache severity and the number of headache days. The discussion piece authors countered that this analysis was constrained by the limitations of the trials included. First, the studies were not designed to perform the same comparison: 3 compared local anesthetics alone with local anesthetics combined with steroids, and the other 6 compared local anesthetics with saline, making it difficult to reach meaningful conclusions using the pooled data. It was not possible to assess the efficacy of the local anesthetics because one-third of the studies used them in both the treatment and control cohorts. More instructive results would have come from dividing the studies into 2 separate groups for analysis.
The authors of the discussion piece also noted numerous problems with diagnosis and patient selection. All of the RCTs were conducted by neurologists who, for the most part, do not support the peripheral trigger theory of migraines. The RCTs included in the meta-analysis did not target the greater occipital nerve for the block but rather used it as a central nervous system conduit. The patients included in these studies were a heterogeneous population and were not selected because their migraines originated in a greater occipital nerve trigger site. In particular, more than half of the participants in the RCT conducted by Naja and colleagues suffered from migraines that originated in the facial area. Failure to respond to a greater occipital nerve block in these patients may simply have been because their migraines originated in a different trigger site.
The discussion piece authors pointed out that patient history, Doppler examination, and tomographic scans should be performed to map out a patient’s trigger sites before surgical decompression is considered. Moreover, patients who are not good candidates for surgery or who do not want to undergo surgery can benefit from injections of onabotulinumtoxin A that target specific trigger sites.
They also indicated that blocks can be very useful diagnostically, but they are not a good option for long-term migraine relief because their effects are short-lived. Meta-analysis investigators did note that the average follow-up of the RCTs included in their meta-analysis was only 4 weeks, which is not enough time to assess long-term efficacy because the literature published on the topic suggests that to obtain sustained relief from nerve blocks, injections typically need to be repeated every 2 to 4 weeks.
In the systematic review, researchers relied on the Jadad scale, which scores numerically from 1 to 5, which, although easy to use, is also subjective, simplistic, and inadequate. They recommended the Cochrane Collaboration methodology as a superior approach to meta-analysis because it thoroughly examines each study according to a large number of objective criteria.
In conclusion, they noted, “Unfortunately, this study leaves more questions than answers. For instance, does the addition of corticosteroids to local anesthetics enhance the diagnostic accuracy of blocks? How do blocks and onabotulinumtoxin A compare in terms of diagnostic accuracy and cost? These will be fodder for future studies [that] can help guide treatment algorithms more effectively.”
Khansa I, Janis JE. Discussion: Greater occipital nerve block for the treatment of chronic migraine headaches: A systematic review and meta-analysis. Plast Reconstr Surg. 2019;144(4):953-955.