Tinnitus as Neuropathy

Did You Know that tinnitus can be a type of neuropathy? I didn’t until recently when an article prompted me to do some research and tap a couple of doctors on the shoulder.

Tinnitus is usually manifested as ringing in the ears, and it ranges in severity from noticeable to disabling. Tinnitus has been around for as long as medical histories have been documented, and one of the earliest cures was actually to bake a loaf of bread, and straight from the oven as hot as you could stand, to cut the loaf in half and hold each piece to the ears until it cooled. In spite of the drama, the cure was also reported as ineffective, but at least the bread could be eaten –once the ear wax was scraped away.

Seriously, tinnitus is one of the possible side effects of chemotherapy, and like peripheral neuropathy is a kind of brain affect. I came across this information as I was chasing down information on the blood-brain barrier. An article I wrote about cognitive affectations resulting from chemo brought a response. A reader commented that it was not possible for chemotherapy to harm the brain because it was blocked from reaching gray matter by the blood brain barrier. They were right that the barrier existed and that it filtered the majority of impurities from the blood, but it did pass proteins through, including  damaging proteins. So on one hand they were right, but on the other hand they weren’t. The way our hearing works is a little more complex than most people think it is. I only just learned that the little hairs that were vibrated by the movement of air we know as sound were not connected directly to some area of the brain that decoded the sounds we hear. I imagined it much like a microphone and amplifier but found it was more like digital processing.  There is actually a little network that makes up a sort of bucket brigade for the signals emanating from the little hairs. There are  five areas of the brain involved in our hearing along with the auditory cortex, and that between the cortex and the rest of the brain exists the caudate and putamen.

There is a categorization that happens in the caudate and putamen that determines where to send the signals from there. When damage occurs from chemotherapy, a sort of feedback loop is accidentally created between there and the brain stem that we end up hearing as the ringing in our ears. It’s a bogus as the sensations felt through peripheral neuropathy. The precise mechanism of this process isn’t known; research is fairly new, but this much has been established. Experimentation has shown that  stimulating the putamen and caudate in certain ways can actually cure or significantly diminish tinnitus. This was accidentally discovered by an ENT physician named Thomas Lowry in 2004. He suffered a stroke which damages his cautate and putamen, and the tinnitus which he’d suffered for 40 years. As a kid he worked on a farm with loud tractors, and it resulted in his affliction. Following his stroke he discovered that his tinnitus was gone, yet no other aspect of his hearing was diminished or even affected. That created a hypothesis which he was able to prove out with five  Parkinson’s patients who were implanted for their Parkinson’s, and also suffered tinnitus. The electrodes were inserted through the caudate and putamen as a matter of course, and they agreed to allow him to stimulate those areas as the electrodes were implanted. Of the five, it cured four and reduced the fifth’s tinnitus significantly. In essence, it was discovered that the feedback loop could be affected and make it stop.

The hearing system employs a tone map, a part of the categorizing system for sound, and a pair of German researchers had luck in subjecting tinnitus patients to 12 hours of music per week with the frequencies of their tinnitus filtered out. I ended up causing the brain to rewrite the tone map, and significantly improved or stopped the tinnitus in their patients. A lot more study needs to go into the subject. But the studies have demonstrated clearly that tinnitus is a disease we can whip, it’s just going to take more research. We also know that there isn’t just one pathway or network on which to focus for the cure. Too many different portions of the brain are involved, and the tinnitus can be induced in any of them. This demonstrates the degree to which the brain is accessible to side effects of chemotherapy. Further, we also have empirical evidence that getting the brain to focus on something unrelated to the tinnitus can cause temporary relief –which is why people speak of their ear ringing as better or worse at different times. The more you can distract the brain away from tinnitus, the less it affects you. That’s exactly the same thing that happens with peripheral neuropathy, and why giving competing senses to the affected areas can diminish the neuropathy at least temporarily while the brain is distracted from it.

Chemotherapy can affect the brain and with the advances in studies happening, our level of knowledge about the brain is gaining all the time. There’s every reason to believe that the more we learn about the brain and the way it can be affected chemically the more we will learn about tinnitus and its bigger, meaner brother, peripheral neuropathy.