The Hyperactive Vestibular Response

Abstract

A hyperactive nystagmic response following routine vestibular stimulation has long been recognized. Central pathology was suspected as responsible for increased postcaloric or postrotatory nystagmus and more recent experimental studies confirmed hyperactive nystagmus after lesions in the cerebellum were created. In order to utilize the hyperactive nystagmus response as an abnormal clinical sign, it was essential to establish criteria for this phenomenon. In 67 normal subjects weak and strong caloric stimulations were performed and by measuring nystagmus frequency at the culmination a wide range of responses was obtained. Using these data as a base line, three groups of hyperactive responses were classified in 1 700 patients. Group A exhibited nystagmus intensities never encountered in the control subjects. Group B represents an increased nystagmus activity at the range which has been found only exceptionally in normals (in 3 out of 133 normal ears). Group C comprises the category of patients in which responses can be considered as pathologically increased although 10% of the normal subjects showed such excessive frequencies. Therefore, our patients in this borderline area may be considered potentially hyperactive. In unilateral occurrence of hyperactivity the pathological designation is further enhanced. The postrotatory responses were similarly classified. A distribution by diagnosis of our 68 patients who had hyperactive responses demonstrates a variety of central abnormalities. Hyperactivity was found in a few instances with peripheral pathology such as otosclerosis or vestibular neuronitis, but the hyperactivity was found on the contralateral side. In a small group of the patients no pathological findings could be obtained except for exaggerated caloric nystagmus. These patients were overly anxious and concerned about their complaints of dizziness and uncertainty. There were 7 out of 68 who had bilateral hyperactivity and were diagnosed as having “psychosomatic disorders”. The study led to the conclusion that the hyperactive vestibular responsiveness is a clinical entity. It can be detected by standard stimulation and reliable nystagmography. It was found to occur in a wide variety of central nervous system disorders and occasionally in neurotic, psychosomatic patients.