I saw a patient recently with known obstructive sleep apnea, who came in for a surgical consultation. He could not tolerate CPAP. He had read about sleep endoscopy and inquired about possibly undergoing this procedure.
Many years ago, a series of papers were published extolling the value of placing patients under general anesthesia, and with simulated sleep along with muscle relaxation, you could identify where obstructions were happening along the upper airway. Back then, I tried this technique routinely just before performing sleep apnea surgery, and found that it didn't give me any more useful information than what I saw with a good exam in the office. With a flexible fiberoptic camera, the entire airway is examined, from the tip of the nose to the vocal folds. There are many different areas for narrowing, but the three major areas are the nose, the soft palate (including tonsils), and the tongue base. In most cases, you'll have multiple areas of involvement. If there's no obvious area of narrowing, then sleep endoscopy can use used in selected cases. If you're doing well on CPAP, all this is a moot point.
One technical reason why sleep endoscopy may not be as useful is due to the positioning of the head during upper endoscopy: The head is extended, or tilted up to straighten out the airway. This is similar to the position that sword swallowers use when inserting swords down the esophagus. We otolaryngologists also use rigid, hollow tubes of various lengths to visualize and manipulate the throat, trachea or esophagus. But by extending the head, the tongue pulls away from the back of the throat, opening up the airway artificially. This is also the maneuver that you're taught to do before administering CPR (and what some of the "anti-snore" pillows attempt to do).
The patient mentioned in the beginning was adamant that sleep endoscopy was necessary to find the right area of obstruction. I respectfully disagreed, stating that he had obvious narrowing and collapse behind his tongue, mainly due to his small jaw. I didn't believe in performing an unnecessary procedure, "just to see," no matter how minor the procedure. He left my office a little upset, but I'm sure he eventually found another surgeon willing to comply with his wishes.