Neuropathy, a type of pain caused by nerve damage, is not a uniform condition but instead may appear in different forms. Botox might offer effective relief for two forms of neuropathy, a new animal study finds. In fact, botulinum toxin produced a lasting reduction of pain in mice suffering from either physical or chemotherapy-related nerve injury.

Cancer patients often experience a pain known as chemotherapy-induced peripheral neuropathy. The peripheral nerves carry sensations (feeling) to the brain and control the movement of our arms and legs. They also control the bladder and bowel. The chemotherapy drugs cisplatin, carboplatin, and oxaliplatin, though, may damage these nerves. Symptoms may include either shooting pain or a loss of feeling in the hands and feet. Sometimes what should be cold to the touch will cause a burning sensation instead.

For many cancer patients, the symptoms disappear over time. Others, unfortunately, are not so lucky. Past research has shown Botox can treat some forms of chronic pain... could it work on neuropathy?

Medical Use

In an examination of Botox B’s effects on neuropathy, Dr. Tony L. Yaksh, an anesthesiology professor at UC San Diego, and his colleagues specifically investigated the effects of local versus spinal injection of botulinum toxin B (Botox B or Myobloc). Botox-B has been approved by the Food and Drug Administration for medical uses, though not for cosmetic purposes. Because it causes temporary muscle paralysis, botulinum toxin’s pain-reducing effects, scientists say, may derive from simple muscle relaxation. However, other scientists suggest Botox supplies analgesic effects. What's the truth?

To begin the current study, the research team induced mononeuropathy (single nerve injury) in one group of mice by cutting a single spinal nerve and then induced polyneuropathy (multiple nerve injury) by giving another group of mice the chemotherapy drug cisplatin. Then, the scientists injected Botox-B, locally and into the spine. Before and after, they measured pain and motor function in the mice.

In mononeuropathy, injecting Botox-B locally — directly into the affected paw — significantly reduced pain. In polyneuropathy, the local Botox-B injection reduced pain in the injected paw only. (This shows the effects of locally injected botulinum toxin are not due to a general spread of Botox-B through the body.) The pain reduction after local injection wore off after two weeks or so.

For polneuropathy, the spinal injection of Botox-B relieved pain in all paws. The spinal injection did not alter normal reflexes, yet it also did not alter other types of pain.

Looking at the cells of these mice showed the researchers that the two types of injections had differing effects in the pain-processing centers of the spinal cord. The researchers say their findings add to previous studies suggesting that botulinum toxin could be a useful new approach to treating neuropathy. Plus, this study adds to the understanding of the differing effects of local and spinal injections.

Source: Park HJ, Marino M, Rondon ES, et al. The Effects of Intraplantar and Intrathecal Botulinum Toxin Type B on Tactile Allodynia in Mono and Polyneuropathy in the Mouse. Anesthesia & Analgesia. 2015.