Definition and Overview
Stroboscopy is a procedure performed to evaluate the vibration of the vocal cords. It assesses the movement of the vocal folds during the production of sound and produces a detailed picture that can be interpreted by the physician. Stroboscopy is performed together with laryngoscopy, which is the examination of the vocal folds.
Who Should Undergo and Expected Results
Stroboscopy is for patients with laryngeal pathologies that typically present with voice changes. Hoarseness of voice or dysphonia is the usual symptom. Other symptoms include breathing difficulty or hemoptysis. The procedure is recommended for these patients to identify the causes of their symptoms. The procedure can likewise diagnose benign conditions including vocal cord nodules, cysts, and polyps and can be used to evaluate patients with vocal cord paralysis. Stroboscopy can also be performed to diagnose malignant conditions, such as laryngeal cancer and to monitor the effectiveness of treatment of various laryngeal pathologies.
Laryngoscopy examines the anatomy of the vocal fold, while stroboscopy examines its function and biomechanics. These examinations, when performed together, can determine a myriad of vocal cord pathologies.
Specifically, stroboscopy evaluates several parameters of the vibration cycle, including fundamental frequency, periodicity, closure of the glottis, and vocal fold symmetry. Studies have shown that performing stroboscopy contributes to the diagnosis of laryngeal disease in approximately 30% of patients.
The limitation of stroboscopy is that the procedure is operator-dependent. This means that the success of the procedure and the quality of the images are dependent on the skills of the physician performing the procedure. The interpretation of stroboscopy results is likewise dependent on the clinician.
In some cases, additional procedures, such as vocal fold injections or endoscopic excision of nodules, may be performed at the same time as stroboscopy.
How is the Procedure Performed?
Stroboscopy is an office procedure, and patients can go home on the same day. It is performed under topical anaesthesia, as patients need to be awake during the procedure to produce specific sounds.
Stroboscopy utilises a flashing light passed through a scope. The movement of the vocal folds is fast but the technology of stroboscopy enables its evaluation at various phases of the vibratory cycle, in real-time and in slow motion. With stroboscopy, the flashes of light coming from the strobe are timed to the voice frequency. Typically, a microphone detects the frequency of vocal fold vibration, which triggers the light source, producing the intermittent flashes of light. When the light flashes at the same frequency as the vibration of the vocal cords, very clear, detailed images are produced but when the light flashes at a lesser frequency than the vibration of the vocal cords, a slow motion effect is created.
Stroboscopy can be performed using either a flexible or a rigid laryngoscope. The advantage of using the latter is that it produces better images, which are bright and magnified. However, rigid laryngoscopy is generally less comfortable for the patient, requiring a higher tolerance for gagging and more cooperation. On the other hand, flexible laryngoscopy is better tolerated and can be used to view the larynx from various angles, even through a small glottic opening. In recent years, technology has greatly improved, allowing improved image quality and resolution.
When performing a stroboscopy, the patient is made to sit in the examination chair at a comfortable height. The head is extended and neck flexed. Topical anaesthesia, usually a spray, is applied to the tongue and the back of the throat. With rigid laryngoscopy, the tongue of the patient is retracted anteriorly to allow the insertion of the scope in the mouth. On the other hand, for flexible laryngoscopy, the scope is inserted through the nose and positioned above the voice box.
Once the vocal folds are clearly visualised, the patient will be asked to make certain sounds, usually pronouncing a vowel, at various pitches (low frequency, high frequency, and mid-range) and volumes. The images generated are transmitted as a video, which can be recorded and viewed repeatedly. Specific details, such as the mucosal wave and the changes in the shape of the vocal folds, can be examined more accurately with stroboscopy.
Possible Risks and Complications
Complications are rare with stroboscopy with most problems encountered related to patient discomfort during the procedure. Pain is minimal, if any, and resolves spontaneously. Problems with the airway, such as breathing difficulty, may occur, but rarely happens. There have also been reports of adverse reactions related to the anaesthetic used or to the scope; however, these also occur infrequently. Other problems may be attributed to other associated procedures performed at the same time. In general, stroboscopy is a safe procedure and is well tolerated by patients.
Kluch W, Olszewski J. [Videolaryngostroboscopic examination of treatment effects in patients with chronic hyperthrophic larynges]. Otolaryngol Pol. 2008. 62(6):680-5.
Low C, Young P, Webb CJ, et al. A simple and reliable predictor for an adequate laryngeal view with rigid endoscopic laryngoscopy. Otolaryngol Head Neck Surg. 2005 Feb. 132(2):244-6.