Less-well appreciated is the occurrence of a slowly progressive vestibulopathy for which no cause can be discerned. The disorder affects men and women alike, with onset in middle or late adult life with the main abnormalities being unsteadiness of gait, which is worse in the dark or with eyes closed, and oscillopsia, which occurs with head movements and is particularly noticeable when walking. Vertigo and hearing loss are absent, as are other neurologic abnormalities. Bilateral vestibular loss can be documented with caloric and rotational testing. Baloh and colleagues, in a report of 22 patients with idiopathic vestibulopathy of this type, found that a significant proportion (9 of 22 cases) had a prior history of prolonged episodes of vertigo consistent with the diagnosis of bilateral sequential vestibular neuritis (see the following text).
This was the term applied originally by Dix and Hallpike to a distinctive disturbance of vestibular function, characterized clinically by a paroxysmal and usually a prolonged single attack of vertigo and by a conspicuous absence of tinnitus and deafness. The entity is, however, more nebulous than most discussions indicate.
This disorder occurs mainly in young to middle-aged adults (children and older individuals also may be affected), without preference for either sex. The patient frequently gives a history of an antecedent upper respiratory infection of nonspecific type, but it is not clear whether this is requisite for the diagnosis. Usually, the onset of vertigo is fairly abrupt, although some patients describe a prodromal period of several hours or days in which they felt “top-heavy” or “off balance.” Persistence of the symptoms for a day or more differentiates the process from Ménière disease. The vertigo is severe as a rule and is associated with nausea, vomiting, and the need to remain immobile.
Nystagmus (quick component) and a sense of body motion are to the opposite side, whereas falling and past pointing are to the side of the affected labyrinth. In some patients, the caloric responses are abnormal bilaterally, and in some, the vertigo may recur, affecting the same or the other ear. Auditory function is normal. Examination discloses vestibular paresis on one side, that is, an absent or diminished response to caloric stimulation of the horizontal semicircular canal. If the patient will tolerate small head movements, the previously described rapid-head-impulse test of Halmagyi and Cremer is one of the best means of demonstrating absent function of one lateral semicircular canal.
Although the symptoms can be quite disabling for a short period, vestibular neuritis is an ostensibly benign disorder. The severe vertigo and associated symptoms subside in a matter of several days, but lesser degrees of these symptoms, made worse by rapid movements of the head, may persist for months. The caloric responses are gradually restored to normal as well. In some patients, there has been a recurrence months or years later, as already mentioned.