When the Research Studies Disagree
Last week’s post about the difficulty inherent in making the diagnosis of Meniere’s disease is only further complicated by two recent studies, both from some of the best researchers in the business. As vestibular testing technology improves, researchers are working to apply those tests to various diseases, and see if any test patterns may solidify a specific diagnosis.
In patients with suspected Meniere’s disease (MD), the description of recurrent episodes of vertigo, lasting minutes to hours, accompanied by unilateral (one ear) aural pressure and tinnitus preceding or during the vertigo episode, is probably the most relevant information needed to make a provisional diagnosis. Vestibular and audiometric tests will either support your suspected diagnosis or not.
In addition to documentation of fluctuating hearing levels, finding asymmetric responses to caloric irrigation can support the diagnosis of MD. Caloric irrigation specifically tests the very low-frequency portion of the vestibular ocular reflex (VOR) that is associated with extremely slow head movement. One could reasonably make the assumption that MD affects this low-frequency portion of the VOR, but what about the high-frequency VOR associated with rapid head movements? Could MD affect the VOR differently from other vestibular disorders and allow high-speed testing to differentiate MD from other conditions known to cause vertigo?
These questions were considered by well known and respected researchers at Vanderbilt University and out of Berlin, Germany. The scientists compared the results of caloric testing and high-speed head impulse testing (VHIT) in patients with MD. Their approaches were slightly different, and you can read the Vanderbilt study abstract here, and the German study abstract here. Their findings were different as well. While the Vanderbilt researchers found no connection between caloric test results and VHIT results, the German study found that VHIT was abnormal in one-third of patients with MD, and abnormal less than 10% of the time in patients with vertigo from another common cause (vestibular migraine).
These were small and recent studies, and much more information will be needed before any conclusions can be drawn. But these differing findings are indicative of the elusive nature of obtaining solid and consistent information in patients with suspected MD. As I have stated in previous posts, there are several theories as to the pathophysiology of MD, and several different treatments offered. This is because no one is absolutely sure of the pathophysiology, and none of the treatments work consistently over a large group of patients.
The unpredictable nature of the severe symptoms associated with MD, and the difficulties associated with diagnosis and treatment make this a particularly stressful condition for the patient. More on that next week.
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