SANTA FE, N.M. Botox is an effective treatment for hyperhidrosis, but the large number of units required is painful unless the clinician uses nerve blocks, George J. Hruza, M.D., said at a conference sponsored by the Skin Disease Education Foundation. However, topical anesthesia is sufficient for the axilla, said Dr. Hruza of the Laser and Dermatologic Surgery Center in Town and Country, Mo.
Treating palmar surfaces with Botox (botulinum toxin type A) requires blocks of the median and ulnar nerves. A radial nerve block is unnecessary, since that nerve innervates the dorsal surface of the hand.
The median nerve is right under the palmaris longus tendon and is best reached in the carpal tunnel. Have the patient touch his or her thumb and little fingers; the nerve will be found at the most proximal crease. One can approach from either side, angling the needle to go under the tendon. If an approach from one side proves unsuccessful, try from the opposite side.
"You can feel it pop in when you get to the carpal tunnel," Dr. Hruza said. "Then inject your anesthetic right in there. There's no big vein or artery there to worry about."
While the ulnar nerve can be reached in the wrist, he prefers to block this nerve by injecting at the elbow between the medial epicondyle and the olecranon process. It's important to avoid injections directly into the nerve, so if the patient shows any sign of paresthesia when the needle goes in, one should back away a bit before injecting. Dr. Hruza recalled one patient who suffered from paresthesia for 4 months as a result of an anesthetic injection into the ulnar nerve.
Treating plantar surfaces requires blocks of the posterior tibial, sural, and superficial peroneal nerves, and, optionally, the deep peroneal nerve.
The posterior tibial nerve is next to the tibial artery, which is easy to find if you can feel the pulse. If you can't feel the pulse, you may want to use Doppler ultrasound to localize the artery. Dr. Hruza has one patient whose tibial artery and nerve are 2 cm out of place. For the first few treatments, Dr. Hruza used Doppler ultrasound; after that, he was able to locate the artery without assistance.
After localizing the artery, insert the needle posterior to anterior, anteromedial to the bone, retract a few millimeters, and inject several milliliters of anesthetic.
The sural nerve is at about the same location on the other side of the ankle. However, there's no artery to guide the injection, which should be placed between the lateral malleolus and the Achilles tendon.
Anesthetize the superficial peroneal nerve by laying down a row of anesthetic in the subcutaneous plane on the front of the foot, extending from the medial to the lateral malleolus.
One may also choose to anesthetize the deep peroneal nerve with a deep injection lateral to the extensor hallucis longus tendon. Dr. Hruza chooses not to block this nerve, because it only innervates the web space between the first and second toes, and only one or two botulinum toxin injections will be made in that location.
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