Vestibular Disturbances in Clinical Otosclerosis

Abstract

The aim of this study was to investigate the preoperative vestibular disturbances in patients suffering from otosclerosis. The material consisted of 60 patients suffering from otosclerosis and 20 control subjects. All patients and control subjects with any previous ear operation or head trauma were excluded. In addition to pure tone tests, speech audiometric tests and if possible loudness balance tests according to Fowler were also performed. The occurrence of spontaneous and positional nystagmus was investigated with ENG. The caloric tests were carried out according to Hallpike and in the rotatory tests Polman's rotatory chair was utilized (Mod. 11 e 111).

In the ENG investigation 20 patients (33,3 per cent) revealed positional nystagmus. In five of them the nystagmus was direction-changing (Nylén's type I), in fourteen the nystagmus was found to be direction-determined (Nylén's type II), and in one patient the nystagmus type was irregular direction-changing (Nylén's type III).

In the caloric tests directional preponderance was verified in 29 cases (48 per cent) when measured from the maximum eye speed and in 32 cases (53 per cent) when measured from the summed amplitude of the slow phase of nystagmus. Twenty-two patients (37 per cent) showed directional preponderance when calculated by the two methods jointly.

Caloric excitability was found to be reduced in 34 patients (57 per cent) (a difference exceeding 20 per cent between the two sides) when measured from the maximum eye speed and in 33 cases (55 per cent) when measured from the summed amplitude of the slow phase of nystagmus. Twenty-five paitents (42 per cent) revealed a lower caloric excitability when calculated by the two methods jointly.

Statistically significantly there are more numerous cases of directional preponderance and lowered caloric excitability in otosclerotic patients than in normal control subjects.

Patients with objective vestibular disturbances showed greater hearing losses at high frequencies than the others. The difference was statistically significant at 4 000 Hz in bone conduction and at 4 000 and 6 000 Hz in air conduction.

The mean thresholds of angular acceleration in otosclerotic patients were 0,49°/sec² to the right and 0,60°/sec² to the left. The corresponding values for deceleration thresholds were 0,58°/sec² and 0,50°/sec². These values are all statistically significantly higher than in the control group.

The mean threshold of angular acceleration in this group was to the right 0,37°/ sec² and to the left 0,32°/sec². The values for deceleration were correspondingly 0,33°/sec² and 0,37°/sec².

Patients suffering from otosclerosis and the control series revealed no statistically significant difference when accelerating from zero to 60°/sec at a rate of 1°/sec² as measured from the summed amplitude of the slow phase of perrotatory nystagmus.

This investigation tends to demonstrate that patients suffering from otosclerosis very frequently show vestibular disturbances. The objective disturbances manifested were firstly, caloric hypoexcitability and elevated thresholds of angular acceleration and deceleration, secondly, directional preponderance and, thirdly, positional nystagmus.