Seventy-two cases of positional vertigo of the benign paroxysmal type were analysed with respect to several clinical findings, especially the characteristic rotatory nystagmus in the positional and positioning tests. The results of the analysis were as follows.
(1) This disease is much more common in the fourth to sixth decades of life than the others. The sex distribution was 26 males and 46 females or a male to female ratio of 1 : 1.7.
(2) The evidence of otitis media, hypertension or head injury was demostrated 31% of the 72 cases.
(3) In 10 patients, gaze nystagmus was seen and of these, two patients had nystagmus in both directions.
(4) In many cases, there was close correlation between the direction of the rotatory nystagmus, the affected ear and the undermost ear in critical position.
(5) Within four weeks after the onset of the symptom, the positional or positioning nystagmus could almost always be detected with the rotatory element, latent period, decrescendo and fatigability. But these nystagmus were absent in about 50% of the patients examined four weeks after onset. The detection rate of the positional nystagmus decreased more markedly than that of the positioning nystgmus.
Although the criteria for the diagnosis of this disease should be strict, at present rather common cases which can not satisfy the criteria are not so rare. For this reason, we concluded that it is important to detect the characteristic rotatory nystagmus in the p sitional and positioning tests within four weeks after the onset of this condition.
