Vestibular neuritis: Involvement and long-term recovery of individual semicircular canals.

OBJECTIVE: In this retrospective study, the aim of the authors was to examine the frequency of involvement of the individual semicircular canals (SCCs) in vestibular neuritis (VN) and to assess the degree of long-term recovery. A secondary aim was to retrospectively determine the usefulness of a three-step bedside oculomotor test (the HINTS-test) for the differential diagnosis of peripheral VN.

METHODS: 44 cases were evaluated during the acute phase and approximately two months later. The gain of the vestibuloocular reflex was determined using video-head-impulse test, carried out using Otometrics ICS Impulse Otosuite Vestibular V 1.2.

RESULTS: In 19 cases (43%), a typical, so called "superior" VN could be diagnosed; in 17 cases (38%), all three SCCs were involved; in 4 cases, an isolated inferior canal involvement was seen; and in another 4 cases, a slight, isolated horizontal canal involvement was registered. Slight, isolated horizontal canal vestibular neuritis causing acute vestibular syndrome has not yet been reported in the literature. A three-step bedside oculomotor examination, the HINTS-test (head-impulse test, examination of gaze evoked nystagmus, and test of skew-deviation), suggested peripheral involvement in all cases with superior pattern VN and in cases when all three SCC were involved. It indicated 'stroke' in cases with inferior pattern and in the cases with isolated involvement of the horizontal canal. At follow-up, the horizontal canal function normalized in 55%, the anterior canal in 38%, and the inferior in 38%. When all cases were pooled, 14 patients recovered completely. In cases with severe initial decrease of gain in the horizontal canal (initial value less than 0.5), the canals had a 50 per cent chance to recover significantly.

CONCLUSION: In vestibular neuritis, in cases with severe decrease of gain in the horizontal canal (initial value less than 0.5), the canal has a 50 per cent chance to recover significantly. The vertical canals have worse prognosis, and especially the inferior canals seldom improve. Slight, isolated horizontal canal vestibular neuritis may cause acute vestibular syndrome, most probably by the same mechanism as full-blown vestibular neuritis. In these cases, the three-step bedside oculomotor test may indicate cerebellar stroke (may be false positive).