Response to "Does scorpion bite lead to resistance to the effect of local anaesthetics?".

Sir,

I read with interest the case report “Does scorpion bite lead to development of resistance to the effects of local anaesthetics?” by Panditrao et al.[1] I was reminded of my anaesthesia days 25 years ago at the Naval Hospital in Bethesda, Maryland, where I first encountered a patient who did not get numb from a bupivacaine subarachnoid block despite a technically well performed procedure. As a resident, I was told that I “must have pulled out of the subarachnoid space”, but I continued to note occasional “resistant” patients as an attending at the Naval hospital in Jacksonville, Florida. None of these patients were likely to have been bitten by a scorpion, and yet they were just as “non-numb” as the patient described in this report. I noted similar “failure” of injections as a pain physician, and concluded that, if the patient did not get pain relief from the local anaesthetic, either I was not in the right place, or the patient did not get numb from my local anaesthetic. I then created a skin test for local anaesthetic resistance, and applied it to patients in my practice. In 2003,[2] I published the results of the evaluation of 1,198 consecutive patients; 250 had a history of difficulty of getting numb from procedures (dentist, sutures, or prior procedures), and were tested with lidocaine, bupivacaine, and mepivacaine subcutaneously. Ninety of those patients (7.5% of the total group but 36% of the tested patients) were found to be hypoesthetic only to mepivacaine, and an additional 43 (17% of the tested patients) were noted to be hypoesthetic only to lidocaine.

Since this is not a particularly rare finding, it has always surprised me that it has not been reported more often. The local anaesthetic “resistance” appears to have a genetic link, since several of my “resistant” patients have family member in my practice who also described “resistance” and were subsequently shown to have limited response to bupivacaine. I currently have an add-on project to an ongoing NIH twin study to evaluate the genetics of local anaesthetic “resistance”. It would be very interesting to see the results of skin testing in this patient, and I encourage clinicians to consider local anaesthetic “resistance” as a possible cause of failure of a technique and to consider trying a different local anaesthetic.