The short increment sensitivity index (SISI) test, published by Jerger in 1959, has been generally used as an indirect method for the diagnosis of recruitment phenomenon. Accordingly, the auditory disorders revealing a negative SISI-score, should include either normal hearing or various types of hearing loss such as conductive, retrocochlear hearing loss etc. We attempted to measure the difference limen for sensitivity of short increment for the purpose of differential diagnosis of retrocochlear deafness. This measurement was termed as difference limen for short increment (DLSI) test. The DLSI-value was measured in dB as a function of intensity jump of short increment.
Nine hundred and forty-two ears with sensorineural hearing loss were tested by DLSI-test routinely as well as by a battery of audiological examinations for differential diagnosis of perceptive deafness. The affected lesions of 73 cases showing abnormally large DLSI-values were investigated. Thirty-five cases showed a large DLSI-value bilaterally. Almost all except for some with head and neck injury and dizziness were patients with brain stem lesions such as cerebellopontine angle tumour, medullar tumour, vertebro-basilar artery insufficiency, cerebellar ataxia, multiple sclerosis. In 38 unilateral cases, a similar tendency was found. It was concluded that the DLSI-test is useful rather as a test for diagnosis of retrocochlear auditory disturbances than as a recruitment examination.