This was a sobering exercise.

As part of the update of Trip I came across this article Efficacy of 8 Different Drug Treatments for Patients With Trigeminal Neuralgia: A Network Meta-analysis. So, I excitedly went to see how good our automated review system did for trigeminal neuralgia.  On an initial examination, of the 8 interventions we did well in just one – so, 1 out of 8 – that’s a fail in anyone’s book. However, it’s not as it first seems….

Lidocaine – we gave it an overall score of 0.01 (indicating a pretty neutral score). This was based on three very small studies.  As such we discount really small studies due to their inherent unreliability.  The network meta-analysis (NMA) also referenced three studies (but not the same three!):

Of which our system only incorporated the top one.  We included two others:

What confuses me is that the two references we didn’t find – from the network meta-analysis (NMA) – are not specifically about trigeminal neuralgia. So, I’m thinking our result is potentially better than theirs!!  I’ve emailed the author for clarification!

Botulinum toxin type A – we scored it as 0.45 (maximum score is 1) so it fits with their analysis.

Carbamazepine – A big failure on our part, we scored it -0.03. We included two studies of carbamazepine, neither of which belonged there. So, we should have reported no trials. It should not have even featured in our results.

Tizanidine – We scored it -0.03 with our system found a single trial A clinical and experimental investigation of the effects of tizanidine in trigeminal neuralgia which was very small and reported “The limited efficacy of TZD“. It scores near zero as, due to the size, we consider it unreliable and therefore discount the score.

The actual NMA referenced one other study Tizanidine in the management of trigeminal neuralgia.  This is not in the Trip index (failure of our RCT system as it is included in PubMed). And that paper reported “The results indicate that tizanidine was well tolerated, but the effects, if any, were inferior to those of carbamazepine.” so hardly a glowing indictment of the efficacy of tizanidine!

I actually think our assessment is reasonable and it seems a stretch of the paper to report it as being superior to placebo (even if they don’t claim statistical significance).

Lamotrigine – we found no trials.  Trip includes one of the trials the NMA included Lamotrigine (lamictal) in refractory trigeminal neuralgia: results from a double-blind placebo controlled crossover trial but for some reason it wasn’t tagged properly. Something to investigate

Oxcarbazepine – we found no trials and Trip includes no trials, so our system didn’t fail it was due to the fact Trip doesn’t contain all published clinical trials.

Pimozide – we found no trials. Trip includes one of the trials Pimozide therapy for trigeminal neuralgia but for some reason it wasn’t tagged properly. Something to investigate.

Proparacaine – We scored it -0.07 and the NMA reported it as no better than placebo. In hindsight I think this is what our system found. The system compares interventions with placebo. So towards 1 = better than placebo, -1 = worse than placebo and 0 = similar to placebo.

So, having gone through each entry I actually think our system did better than before.

Correct

  • Botulinum toxin type A
  • Proparacaine

Uncertain, I think our system did better than the paper (on the evidence I’ve seen)

  • Lidocaine
  • Tizanidine

Wrong, due to finding no trials with no trials in Trip and not reporting the intervention (so not too bad as we didn’t make any claim on efficacy)

  • Oxcarbazepine

Wrong, due to finding no trials but missing trials in Trip and not reporting the intervention (so not too bad as we didn’t make any claim on efficacy)

  • Lamotrigine
  • Pimozide

Failure, due to us falsely including two trials and making a ‘claim’ for it’s efficacy. It should not have featured at all!

  • Carbamazepine

Conclusion: When I first looked I was fairly depressed by the results. However, now I’ve understood them I’m actually quite pleased.  Of the eight interventions in the NMA we only clearly got one wrong (Carbamazepine) where we wrongly assigned a score.  We omitted giving a score for three (but we should have for two of those Lamotrigine and Pimozide) however, as that does not create any prediction by our system I’m fairly relaxed about it – but will still investigate why.  There are still two unclear results (Lidocaine and Tizanidine) where I actually think our results are better – but will wait to see what the authors report back.

Interestingly the CKS guidance on trigeminal neuralgia (sorry only available in the UK) suggests using carbamazepine as the first line, before stating:

If carbamazepine is contraindicated, ineffective, or not tolerated, seek specialist advice. Do not offer any other drug treatment unless advised to do so by a specialist.

This indicates a lack of faith in any other intervention! CKS reference the NICE guidance on Neuropathic pain in adults which has a section “2.3 Carbamazepine for treating trigeminal neuralgia” which reports:

Carbamazepine has been the standard treatment for trigeminal neuralgia since the 1960s. Despite the lack of trial evidence, it is perceived by clinicians to be efficacious. Further research should be conducted as described in the table below.

So, it’s not surprising there are no trials but the recommendation itself seems to lack an evidence base.

Bottom line: Initial a ‘fail’ but actually a ‘reasonable pass’

 

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