If you break your arm on Tuesday, it will still be broken on Wednesday when you get in to see your doctor. And it will still be broken when you are sent for an X-ray, and there will be a clear picture of the break. All in all, this is a relatively straightforward and easy diagnosis.
Meniere’s disease, on the other hand, causes severe symptoms lasting for minutes to hours, but by the time you see a doctor, the symptoms may be gone. Alternatively, you may end up in an Emergency Room where staff are great at managing life-threatening conditions, but rarely have the tools or training to make a diagnosis based on the clinical presentation of a Meniere’s attack.
By the time you get to a vestibular specialist you may have no symptoms, or your vestibular test results may be (and in the case of Meniere’s disease, usually are) inconclusive. In the early stages of Meniere’s disease, vestibular tests performed between episodes are often normal. After several episodes there is often a decrease in low-frequency hearing measurable between episodes, and there may be a measurable difference between ears when performing caloric irrigations. The problem is that some times there is no measurable caloric difference, sometimes the affected ear is weaker, and sometimes the affected ear is stronger. A Johns Hopkins study published in 2000 explored this phenomenon. Here is a direct quote from the study abstract by Leonard Proctor:
Caloric weakness was demonstrated in 58% of patients on the involved side and in 19% on the normal side. Complete paralysis was found in 7%. Directional preponderance was seen in 33% of patients and completely normal scores in 27%. During the course of the disease, responses become weaker in 26% of patients and stronger in 11%. Of 39 patients tested more than twice, 26% showed both increases and decreases in caloric responses. After an acute attack, only one of eight patients showed a depressed response on the diseased side, and three showed an increased response. Spontaneous nystagmus, seen within 24 hours of an attack in 54 cases, was directed away from the diseased ear in only about one half of the cases. Benign paroxysmal positional vertigo was found in 44% of these patients.
Can this inconsistency and variability be explained? Well, actually, it can. While the unaffected ear produces a stable response over time, the affected ear is fluctuating up and down. During an attack, the labyrinth is “irritated,” causing a temporary increase in firing rate. With each episode, the affected labyrinth is gradually weakened and the resting state between episodes will be less than in the unaffected ear. In the early stages, the relative weakness on the affected side may not be measurable. A caloric exam may catch this fluctuation at any point in the up and down cycle.
As a diagnostician, I find serial caloric testing difficult if not impractical. On the other hand, serial air/bone audiograms are easy, and the patient does not have to travel to a specialty clinic to have this done. Our clinic protocol for patients with suspected Meniere’s is to have them come in immediately when they are experiencing any symptoms of aural fullness, increased tinnitus, decreased hearing or vertigo. We do a quick air/bone audio and view for nystagmus under video goggles. If they live far away, we suggest they go to a local Audiology or ENT clinic for a quick audiogram. Documentation of fluctuating sensorineural hearing loss goes a long way in firming up a suspected diagnosis of Meniere’s disease.
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