[Pulse oximetry and obstructive sleep apnea].

We report a case of a 54 years old man, treated with Methylphenidate (Ritalin) because of narcolepsy, who was referred with suspected vertebro-basilar insufficiency. In the hospital, apnoea during sleep attacks were observed. A polysomnography showed marked obstructive sleep apnoea with a disturbed hypnogram, but during the apnoeas the oxygen saturation only decreased by three to six percent. If a patient suspected for obstructive sleep apnoea has only small desaturations, an oximetry can be insensitive as the only "sleep examination", and a full polysomnography is recommended.