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Dizziness Due to Loss of Vestibular Function in Both Ears You have had several spells of vertigo in the past, but now you are constantly dizzy and off balance. When you walk, the area in front of you seems to bounce up and down. When you ­ ride in an automobile, your vision becomes unstable and road signs seem to vibrate or blur, becoming clear when you stop. The balance prob­ lem is worse in the dark, where you may stumble and fall. Bilateral vestibular failure (BVF) occurs when the balance mechanism of both ears is damaged. By contrast, vertigo is a symptom of asymmetric, or one-­ sided, damage. BVF can occur with any disease that damages both ears, ­ either one ear­ after the other or both ears at the same time. Most such diseases ­ will also damage hearing, so any person who is deaf in both ears might have BVF. Some drugs and several ge­ ne­ tic disorders can selectively damage the vestibular part of the inner ear and cause BVF without affecting hearing. Anyone who is taking drugs that may be toxic to vestibular function needs to know how to recognize early symptoms of damage so the drug can be stopped before the damage is severe. The main symptoms of BVF are imbalance when standing and walking and visual distortion with head movement, called CHAPTER  9 Constant Dizziness for Months, Years 142 oscillopsia. Since one of the main functions of the vestibular system is to keep the eyes stable when the head is moving, it is not surprising that ­ after that system is damaged, the eyes move when the head moves and visual acuity is degraded. In order for a person with BVF to see clearly, she must stop and hold her head perfectly still. Some ­ people with BVF find that they must hold their heads still with their hands on their chins in order to read. BVF initially came to the attention of most doctors in the early 1940s, when a frequent treatment for Ménière’s disease involved cutting the vestibular nerve. As noted in chapter 3, a small percentage of patients with Ménière’s disease eventually develop disease in both ears—­ and in the past some patients had their vestibular nerves cut on both sides. ­ After the second surgery, in which the vestibular nerve was cut on the side opposite to that of the first surgery, ­ these patients had severe prob­ lems with balance and found their vision blurred when they ­ were in motion. In some cases the symptoms of BVF ­ were worse than the symptoms of Ménière’s disease that surgery was intended to cure. For this reason, surgeons now rarely cut the vestibular nerve on both sides. Awareness of BVF increased ­ after streptomycin became widely used, around 1950, when it was one of the only treatments for tuberculosis. By then, tuberculosis had killed more than 1 billion ­ people. But streptomycin can be extremely toxic to the vestibular system. ­ After receiving streptomycin for suspected tuberculosis, a doctor named John Crawford described his symptoms in a famous 1952 letter to the editor of the New­ Eng­ land Journal of Medicine, “Living without a balancing mechanism .” He reported his feeling of imbalance to his doctors, but they disregarded the symptom and continued his streptomycin treatment. On his daily walks he had difficulty seeing the 143 DIZZINESS DUE TO LOSS OF VESTIBULAR FUNC TION­ faces of passersby and developed the tactic of saying hello to every­ one so as not to offend any friends he could not recognize . When contacted years ­ later, when he was in his eighties, Dr. Crawford said that he still had the symptoms of BVF but had adapted and lived a reasonably normal life. Streptomycin is now rarely used, but another antibiotic in the same class, gentamicin, is widely used and equally toxic to the vestibular system. It is remarkably selective for the vestibular system, which means that it affects that system but usually does not affect hearing. Gentamicin is an extremely popu­ lar drug for use in the hospital ­ because it kills many dif­ fer­ ent types of bacteria, and it is inexpensive. In some countries , such as China, it is one of the most commonly used antibiotics. While in the United States at least a hundred patients a year are recognized to develop BVF due to gentamicin toxicity, in China the number is likely in the thousands. Gentamicin is excreted by the kidneys, so it should not...


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