Unusually low oxyhemoglobin saturation on polysomnography

A 22-year-old male college student with prior diagnoses of mild obstructive sleep apnea, delayed sleep-wake phase disorder, and inadequate sleep hygiene presented to the sleep clinic for an evaluation of ongoing daytime hypersomnolence despite the use of mixed dextroamphetamine/amphetamine salts extended-release preparation (Adderall XR) 20 mg two times a day prescribed by his primary care provider for sleepiness. He reported going to bed at 10:00 pm, falling asleep quickly, sleeping throughout the night until 8:00 am, and not napping during the daytime but feeling extremely sleepy with an Epworth Sleepiness Scale score of 20/24. He described waking with a dry mouth but did not endorse snoring, snort arousals, or headaches upon awakening. There was no history suggestive of leg movements at night, cataplexy, hypnagogic/hypnopompic hallucinations or sleep paralysis. On examination, the patient had a patent oropharynx (Friedman grade I), neck circumference of 45 cm, body mass index of 36.63 kg/m ² , and normal blood pressure. Download from his continuous positive airway pressure (CPAP) device set at 11 cm H2O pressure showed consistent usage for the entire reported sleep duration, minimal air leak, and a low residual apnea-hypopnea index. To evaluate his hypersomnolence further, the patient was tapered off his stimulant medication and two-week actigraphy followed by overnight polysomnography and Multiple Sleep Latency Testing (MSLT) was ordered.