Needle-free anaesthesia prior to botulinum toxin type A injection treatment of palmar and plantar hyperhidrosis

Abstract

Conflicts of interest: none declared. Sir, Botulinum toxin type A (BTX‐A) has emerged as a new technique to treat intractable cases of focal hyperhidrosis (HH).1 Injections on the palms and soles, although effective, are very painful and need some form of anaesthesia. Peripheral nerve blockade, the standard method of anaesthesia used, may have serious drawbacks,2 particularly when used repeatedly. Needle‐free anaesthesia may offer an alternative solution.3 The technique involves the use of needle‐free injection of 0·02–0·04 mL of 2% lidocaine without adrenaline prior to BTX‐A injection with needle. The mixture of lidocaine and BTX‐A does not jeopardize toxin potency.4 The device used to achieve needle‐free anaesthesia is the MED‐JET® MBX (Medical International Technologies, Montreal, QC, Canada; Fig. 1), which has the advantage over similar devices such as the Dermojet® (Robbins Instruments, Chatham, NJ, U.S.A.), of providing an adjustable range of volumes and pressures necessary to control the penetration depth. For palmar HH, the volume is adjusted to 0·02 mL per spurt (range 0·01–0·1 mL) and the pressure system set to 120 p.s.i. A first shot of lidocaine is discharged at the centre of the palm and if a superficial skin weal fails to appear, the pressure is steadily raised until a weal is obtained. Once the weal is formed, injections are evenly distributed at 1·5–2‐cm intervals over the whole palmar surface including the fingers. For plantar HH, higher volumes (0·04 mL) and pressure may be required to produce an anaesthetic weal. On average, 50 sites per hand or 30 sites per foot are injected in this manner. BTX‐A is injected through a 31 gauge needle preferably after each sequence of four or five lidocaine weals (Fig. 2). Injections are carried out intradermally rather than subcutaneously in an attempt to reduce the incidence of significant muscular weakness.5 Universal precautions including full‐face shield or face mask and protective eyeglasses are taken to avoid contamination caused by potential blood splatter. The device has recently been approved by Health Canada, and U.S. Food and Drug Administration approval is pending.