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Docetaxel is effective against numerous tumors, mainly in metastatic breast cancers; however, it can lead to other conditions, in particular cutaneous reactions, such as onycholysis and hand–foot syndrome. The ungual toxicity of docetaxel is well-known and occurs in 40–50% of cases. The mechanism of this toxicity is of neurogenic origin. Local symptoms are due to incorrect information resulting from one or more lesions or anomalies in the nervous pathways that direct these painful nerve impulses to the sensory cerebral cortex. During large-scale release of neuromediators, particularly substance P, the inflammation becomes neurogenic. As substance P is one of the main agents implicated in inflammation of this type, any molecule preventing its release or blocking its post-synaptic action could be a potential inhibitor of this inflammation, which is deleterious to nails. Ungual side effects following chemotherapy often involve progressive destruction of the nail that can lead to intense localized pain (onycholysis). The nail may crumble or even fall off, causing problems with walking when toenails are involved or gripping difficulties when fingernails are altered. Wasner et al.1 reported a case of a patient suffering from a cancerous tumor in the right breast, who was rendered paralyzed in the right arm following infiltration of the brachial plexus by this tumor. Treated with docetaxel, no ungual side effects appeared on the right (paralyzed) side, while significant ungual side effects were observed on the patient’s left hand. The article underlines the neurogenic mechanism of side effects linked to chemotherapy. Substance P released under the effects of chemotherapy is described as pro-inflammatory and vasodilatory.
A new hydrophilic-film-forming solution containing lithium, Evonail®, acts by interfering with the signalling mechanisms determined following activation by the substance P receptors, as shown by Boisnic et al.2 In this in vitro study, a human sebocyte culture model was stimulated by substance P and corticotrophin-releasing hormone (to mimic stress conditions; see Figure 1A) and the mineral constituents of Evaux thermal spring water (including lithium)—both pure and diluted by 50%—had an inhibitory effect on sebocyte proliferation (see Figure 1B). To clinically illustrate these preliminary results, some clinical case reports follow.