Ask the Doctors by Eve Glazier, M.D. and Elizabeth Ko, M.D

Having a Morton’s Neuroma Is a Pain in the Foot

Dear Doctor: I have Morton's neuroma in both feet, and my podiatrist has recommended surgery. I really don’t want to have surgery, so I am desperately looking for another remedy. I read about a drug that was being fast-tracked by the FDA. Has it been approved yet?

Dear Reader: Morton’s neuroma is basically a pinched nerve in the ball of the foot, most often between the third and fourth toes. The nerve, which carries sensation from the toes, becomes swollen due to a benign growth. This allows the nerve to rub against, bump into or become trapped by the bones and connective tissues of the mid-foot. This results in sensations ranging from numbness, burning and tingling in the forefoot, the toes or both, all the way to outright -- and sometimes significant -- pain. Some people also experience swelling between the toes.

The cause for Morton’s neuroma isn’t fully understood. However, contributing factors include narrow shoes, which squeeze the toes; high-heeled shoes, which exponentially increase the pressure exerted on the ball of the foot; and damage to the nerve due to trauma, inflammation and illness. Biomechanical issues such as flat feet or high arches, which can lead to instability around the joints of the toes, are believed to play a role. Bunions or hammer toes are also considered to be risk factors for developing Morton’s neuroma. The repeated stress associated with high-impact sports, such as running and basketball, can also give rise to a neuroma.

Some neuromas can be diagnosed with a physical exam to locate tenderness in the ball of the foot, or to identify a mass. Some people report a sensation of clicking between their toes. Imaging tests such as ultrasound can isolate tissue abnormalities associated with a neuroma. Although an X-ray won’t diagnose the condition, it can rule out other potential causes, such as a stress fracture.

Treatment depends on the severity of the condition. Many people find relief with a change of footwear. Flat-soled shoes with a roomy toe box and adequate padding beneath the ball of the foot can relieve pressure and protect the affected area. Custom shoe inserts, known as orthotics, can also offer relief. Some people require anti-inflammatory medications or cortisone injections to manage pain and inflammation. In severe cases, an outpatient surgery to remove the inflamed and enlarged nerve may be necessary.

The drug you’re asking about, known as CNTX-4975, is being developed to address moderate and severe knee pain associated with osteoarthritis. It’s an intriguing approach to pain management, which uses a laboratory-derived version of a substance called capsaicin, one of the compounds that give chili peppers their heat. The idea is that when delivered via an injection, the capsaicin will interfere with the neurological process that transmits pain signals to the brain.

You’re correct that at one point, the drug was being considered for use in Morton’s neuroma. However, the company developing the drug has decided to focus its use for knee pain due to osteoarthritis. Clinical trials of the drug are ongoing.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)