Mechanism of action of stinging nettles.

OBJECTIVE: Inadvertent exposure to the ubiquitous weed, Urtica dioica, called "stinging nettles" produces an immediate stinging and burning sensation on the skin. This investigation evaluates the structural effect that stinging nettle spicules may have on the clinical manifestation of these symptoms. This hypothesis was investigated by exposing murine skin to stinging nettles and then evaluating the skin using electron microscopy. It was hypothesized that the mechanism of action of stinging nettles is both biochemical and mechanical, which may have clinical significance regarding treatment for acute exposure. METHODS: Fresh post-mortem dermis samples from the carcasses of genetically modified hairless mice were brushed under the stem and leaf of a stinging nettle plant, mimicking the clinical method of exposure a patient might experience. Another set of mouse skin samples was obtained but not exposed to the nettles. Both sets of skin samples were imaged with scanning electron microscopy. RESULTS: The skin samples that were not exposed to nettle leaves were uniform, with occasional striated hairs on the skin surface and no nettle spicules. The skin samples exposed to nettle leaves showed many smooth nettle spicules piercing the skin surface. A few spicules retained their bases, which appear empty of any liquid contents. CONCLUSIONS: The mechanism of action of stinging nettles dermatitis appears to be both biochemical and mechanical. Impalement of spicules into the skin likely accounts for the mechanical irritation in addition to the known adverse chemical effects of stinging nettles. Further investigation of treatment modalities is warranted.

Modified transthecal digital block versus traditional digital block for anesthesia of the finger.

PURPOSE: This study compared the modified transthecal digital block (MTDB) technique with the traditional digital block (TDB) according to the degree of discomfort caused by injection and to the onset and the duration of anesthesia. METHODS: This was a prospective, randomized, double-blinded, and controlled study. The same investigator performed all blocks to the middle fingers of each hand. The hand anesthetized and type of block (TDB or MTDB) received first were both randomized. An orientation was given to the 25 participants detailing how to evaluate their own degree of anesthesia. This orientation included establishing a baseline of sensation with a safety pin, a description and diagram of 12 zones of the finger, an explanation of the 10-cm visual analog pain scale, and an explanation of how to record anesthesia progress in the fingers. On completion of each block, the subjects recorded the degree of pain and time to anesthesia in each finger zone. RESULTS: Twenty-five subjects received 1 TDB and 1 MTDB for a total of 50 blocks. The TDB received a mean rating for pain of 2.972 versus 2.784 for the MTDB (p =.579). The TDB took 3.91 minutes on average to take effect, whereas the MTDB took 7.16 minutes, a difference of 3.25 minutes. This was statistically significant in 11 of the 12 zones. Overall, return to sensation from the MTDB took effect 4.63 minutes sooner than the TDB: on average 85.19 minutes versus 89.82 minutes, respectively. This was statistically significant in 2 of the zones. CONCLUSIONS: The effect of MTDB is equal to that of TDB in terms of pain perception. For the dorsal and radial proximal zones, the TDB appears to have better distribution of anesthesia. The MTDB has slower onset to anesthesia than the TDB.