End-organ and drug-induced vestibular nystagmus

The occurrence of spontaneous, positional and paroxysmal positional nystagmus was studied in patients with end-organ lesions, and in subjects with drug-induced central vestibular nystagmus. Repeated vestibular examination using electronystagmography for assessment of spontaneous and positional nystagmus in the standard head positions was carried out. The findings indicate that the paroxysmal positional nystagmus is the most frequently seen nystagmus prior to its disappearance in end-organ induced nystagmus and also the most frequently seen in drug-induced nystagmus. The direction changing type of nystagmus was very frequently encountered in end-organ lesions. These findings indicate that the type of horizontal vestibular nystagmus by itself is of no diagnostic value in localizing the site of the lesion and that the various types reflect different degrees of vestibular compensation that occur prior to their disappearance. The value of various classifications of positional nystagmus lies mainly in that they help describe the nystagmus clinically.