The SISI test is an audiometric and completely risk-free test procedure of ENT medicine, which corresponds to a simplification of the Lüscher test and is used in the assessment of sensorineural hearing loss. In the course of the test, an audiometer is used to play suprathreshold volume jumps into the patient’s ears, which are either detected by the test person or remain undetected. The evaluated percentage of detected loudness increases helps to assess whether there is a positive or negative recruitment.
What is the SISI test?
The test belongs to the group of suprathreshold hearing tests because it offers the patient volume fluctuations above the hearing threshold. SISI stands for “short increment sensitivity index” and refers to a subjective and audiometric test procedure in otolaryngology. The test belongs to the group of suprathreshold hearing tests, since the patient is offered volume fluctuations above the hearing threshold. The method has a relevance mainly for recruitment, i.e. a psychoacoustic phenomenon in inner ear disorders. The SISI can be used to draw conclusions about the cause of sensorineural hearing loss. The test results can be used to diagnose positive or negative recruitment. The test was developed in 1959 by James Jerger and colleagues. At the time, this development was based on the Lüscher test, which is based on the same principles, but requires significantly more effort on the part of patients and test personnel.
Function, effect, and goals
In the SISI, intensity differences in the level range are measured based on the excitation of hair cells in the inner ear. The basis for the test is the assumption that inner ear hearing impaired people perceive small level variations as clearly as hearing healthy people. An audiometer is required to perform the SISI. Tones with a suprathreshold level are played to the patient through headphones. In addition to many hospitals, most ENT clinics and practices also have such an audiometer. As a rule, the SISI is only performed on patients suffering from a hearing impairment of at least 40 dB. The test is not used for lower hearing thresholds, as the test procedure then lacks significance. The threshold of 60 dB should not be exceeded during the entire test procedure. Since the test belongs to the subjective audiometric test procedures, the patient’s cooperation during the SISI is explicitly required and is even crucial for the reliability of the results. During the course of the test, the subject is given tones of various levels on the ears through headphones, which become progressively louder by tiny dB jumps. The patient is asked to comment on detected db jumps. The test is opened by a test tone level that is about 20 dB above the individual hearing threshold. This test tone level is periodically amplified for short durations. As a rule, the time interval between the volume changes is about five seconds. The amplitude of the intensity change is usually one dB at a time. The duration of each tone amplification is one second. After each change in tone intensity, the patient indicates whether he or she detected a jump in level. At the beginning of the audiometry, the jump is usually clearly recognizable to him. Often, however, toward the end of the examination, the detectability fades. The data collected during the examination are still documented during the SISI and later evaluated by the staff in relation to recruitment. For those with normal hearing, a level change of one dB above the hearing threshold is not detectable. If, on the other hand, a cochlear sensorineural hearing loss is present, then the patient 20 dB above the hearing threshold will usually detect volume changes of one dB without a doubt. If, on the other hand, the sensorineural hearing loss is retrocochlear, for example due to damage to the auditory nerve, the intensity changes are not detected in the SISI test. The evaluated test result corresponds to the percent of detected loudness changes and is used to diagnose recruitment. Values between 60 and 100 percent are associated with positive recruitment. Values between 0 and 15 percent are associated with negative recruitment. In the test range of 0 to 30 percent, there is thus a high degree of certainty that no cochlear hearing loss is present. In the range between 70 and 100 percent, on the other hand, cochlear hearing loss can be assumed with a high degree of probability.
Risks, side effects and dangers
The SISI is inseparably related to the Lüscher test, on which James Jerger officially based its development. As with the Lüscher procedure, the SISI focuses on the increased detectability of fluctuations in sound intensity that patients with cochlear sensorineural hearing loss exhibit compared with those with normal hearing. Ultimately, the SISI represents a methodological simplification of the Lüscher test procedure and has made the basis of the Lüschner test applicable on a large scale. Consequently, the SISI is neither associated with great effort nor with risks or side effects for the patient. Nevertheless, the SISI is not usually applied to young children, nor to people with mental retardation. Neither is the subjective test suitable for unwilling test subjects. Since the patient’s cooperation is crucial to the accuracy of the data collected, the patient must be able to understand the test procedure and must also be willing to cooperate. However, the results of the SISI are not always meaningful even on willing patients. For example, in the transition range between 15 percent and 60 percent detected loudness change, no clear conclusion can be made regarding recruitment or the likelihood of sensorineural hearing loss.
