Short Increment Sensitivity Index (SISI). The Short Increment Sensitivity Index (SISI) test assesses a patient’s ability to detect small changes in the intensity of pure tones. Patients with cochlear lesions can better appreciate these small changes compared to normal subjects or those with conductive or retro-cochlear dysfunction. Thus, the SISI test is used to differentiate cochlear from retro-cochlear lesions.
Procedure: A continuous, supra-threshold tone (20 dB above the hearing threshold) is presented to the patient for 2 minutes. The tone is then increased by 1 dB every 5 seconds, with 20 such increments. The patient is instructed to count the number of increments they hear.
Interpretation:
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- Conductive deafness: SISI score < 15%
- Nerve deafness: SISI score 0–20%
- Cochlear deafness: SISI score 70–100%
Disadvantages: Patients with severe deafness (above 85 dB) cannot be tested with most clinical audiometers, and the test requires active cooperation from the patient.
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Thereafter, the tone is raised by 1 dB every 5 seconds and 20 such tones are given. The patient is instructed to count the number of tones heard.
Learning resources.
- Scott-Brown, Textbook of Otorhinolaryngology Head and Neck Surgery.
- Glasscock-Shambaugh, Textbook of Surgery of the Ear.
- Logan Turner, Textbook of Diseases of The Nose, Throat and Ear Head And Neck Surgery.
- Rob and smith, Textbook of Operative surgery.
- P L Dhingra, Textbook of Diseases of Ear, Nose and Throat.
- Hazarika P, Textbook of Ear Nose Throat And Head Neck Surgery Clinical Practical.
- Mohan Bansal, Textbook of Diseases of Ear, Nose and Throat Head and Neck surgery.
- Anirban Biswas, Textbook of Clinical Audio-vestibulometry.
- W. Arnold, U. Ganzer, Textbook of Otorhinolaryngology, Head and Neck Surgery.
- Salah Mansour, Textbook of Comprehensive and Clinical Anatomy of the Middle Ear.
- Susan Standring, Gray’s Anatomy.
- Ganong’s Review of Medical Physiology.
Author:
Dr. Rahul Bagla
MBBS (MAMC, Delhi) MS ENT (UCMS, Delhi)
Fellow Rhinoplasty & Facial Plastic Surgery.
Renowned Teaching Faculty
Mail: msrahulbagla@gmail.com
India