I once went to a talk on treatment of neuropathic pain and much to speaker’s surprise I told him I hated that term. Reason being, neuropathic pain with considerable peripheral sensitization (coming from the skin tissues) will respond nicely to neuropathic pain drugs like gabapentin but nerve pain syndromes coming from brain, spine of nerve root near spine ( sciatica) do not. Then comes along a study that lumps them all together – most probably spinally related and the notice no benefits from topical meds. That is nothing nerve shattering – most neuropathies respond poorly to the same drugs orally – a study using drug combinations orally only got 23.7% significant response rate: I wrote about it here:
Severe Neuropathic Pain – Only 1/4 Respond to Standard Drug Protocols – What Else Is There?
based on article:
Moulin, Dwight E., et al. .
Long-term outcome of the management of chronic neuropathic pain: a prospective observational study.
The Journal of Pain 16.9 (2015): 852-861.
I have always been reluctant to use topical compounded agents for pain for the number needed to treat could be high as is the cost. Now, recent analysis suggests they are no good at all. What might be needed is some common sense – certain pain conditions induce considerable skin peripheral sensitization and that becomes part of the pain – that skin sensitization is fair game for topicals. Example? – I have a blog note on how to get rid of a migraine headache with 6 minutes skin pressure on temporal and occipital nerves:
Finger pressure can relieve many migraine headaches
what will be left afterwards is the skin sensitization in frontal scalp tissues which a topical could help.
Compounded Topical Pain Creams to Treat Localized Chronic Pain: A Randomized Controlled Trial
Robert E. Brutcher et al
Ann Intern Med. 2019. in press
Most of the original neuropathic pain studies were done with post-herpetic neuralgia and diabetic peripheral neuropathy. These two have a large peripheral sensitization and respond to oral and topical meds.
Sciatica responds poorly to cymbalta, gabapentin and pregabalin and since over 1/2 of neuropathic pain is from that, present study did not find any use for topicals.
This gives a rough idea of burden of peripheral sensitization and where one might find benefit from topicals.