to the editor: Drs. Suleiman and Johnston make a valuable contribution to the literature with their article “The Abdominal Wall: An Overlooked Source of Pain.”1 Neuromas forming in postsurgical scars are a common source of abdominal wall pain. The patient does not always correlate this pain with the scar, because the pain may not localize to the scar and because of a lack of temporal correlation with surgery (neuromas in scars may not express themselves for days or weeks after surgery). Scar sensitivity can be tested by applying a digital shearing force to the scar or by irritating it with an open paper clip.
Capsaicin cream (0.075 percent), available over the counter, offers an alternative for treating patients who fear syringes and trigger point injections. Capsaicin cream is readily absorbed and selectively binds to the vanilloid receptor subtype 1 (VR1). Capsaicin-sensitive nerves are nociceptors that give rise to small diameter, unmyelinated C fibers (rarely, Ad fibers). The signal propagates to dorsal horn ganglia, evoking release of substance P, somatostatin, and calcitonin-gene related peptide (CGRP).2 With repeated exposure to painful stimuli, VR1 receptors become desensitized. This phenomenon underlies the seemingly paradoxical use of capsaicin as an analgesic. Capsaicin cream has been used to treat osteoarthritis, rheumatoid arthritis, diabetic neuropathy, interstitial cystitis, and many other forms of hyperalgesia and allodynia.3
The off-label use of capsaicin cream for treating painful scars is heretofore unreported. Based on our experience (nearly 20 cases since 1994), treating scars with capsaicin may provide permanent pain relief. These results contradict the effects of capsaicin in arthritis, where pain relief requires regular use of capsaicin. Capsaicin cream also alleviates other syndromes described by Drs. Suleiman and Johnston,1 such as rectus nerve entrapment and postherpetic neuralgia.
Patients must be carefully instructed on the topical application of capsaicin. Apply a very small amount to the scar (“the size of a rice grain”), and massage cream into tissues until little or no cream remains on the surface. Gloves should be worn during application, or hands should be washed carefully and immediately after application. Introducing medication into the eyes or broken skin must be avoided. Advise patients that a burning sensation may occur for up to an hour after application. The transient sensation usually disappears after a few days of regular application. This burning sensation is made worse by heat, humidity, sweating, and bathing in warm water. As the pain diminishes after a few days, the patient can apply more cream (“the size of a pea”), and massage can be applied more vigorously, similar to an osteopathic “myofascial release” procedure.4
Compliance can be an issue with capsaicin, because the cream needs to be applied three times a day, at least initially. Pain relief usually begins within two weeks; thereafter the dosage interval can be reduced to twice a day. After two or three months, the patient should try discontinuing the medication. In most cases, the capsaicin has broken the pain-muscle spasm-pain cycle, and the abdominal wall pain does not resume.
in reply: We thank Dr. McPartland for sharing his experiences with using capsaicin cream for the treatment of pain in abdominal wall scars. This use of capsaicin has not been reported previously in the medical literature. However, it makes perfect sense to expect capsaicin to be helpful for this indication. Capsaicin may also be useful in other types of abdominal wall pain in which local irritation of nerve endings may be responsible for the pain. Use of capsaicin is a simple and inexpensive intervention, and there seems little to lose in trying it if other measures fail.