What is the best next step for a 23-year-old woman experiencing excessive daytime sleepiness, despite getting 9 hours of sleep each night, with unrefreshing naps and a history of sudden sleep attacks?

Polysomnography Followed by Multiple Sleep Latency Test

The best next step is polysomnography (PSG) followed by a multiple sleep latency test (MSLT) (option c). This patient's clinical presentation—excessive daytime sleepiness despite adequate sleep duration, frequent unrefreshing naps, and sudden sleep attacks while driving—strongly suggests a hypersomnia of central origin, most likely narcolepsy.

Clinical Reasoning

Why PSG Followed by MSLT is Required

For diagnosis of suspected hypersomnias of central origin, patients require overnight polysomnography followed by a multiple sleep latency test. 1 The MSLT is an electrophysiologic test involving 4-5 daytime naps at 2-hourly intervals that assesses latency to sleep onset and the type of sleep that occurs. 1

The diagnostic criteria are specific:

• A mean sleep latency of ≤8 minutes plus the presence of REM sleep on ≥2 naps are indicative of narcolepsy 1
• The MSLT is indicated as part of the evaluation of patients with suspected narcolepsy and may be useful for suspected idiopathic hypersomnia 2
• PSG and MSLT can diagnose narcolepsy, idiopathic hypersomnia, and parasomnias 1

Why the Overnight PSG Comes First

The overnight PSG is essential to:

• Rule out obstructive sleep apnea or other sleep disorders that could explain the excessive daytime sleepiness 1
• Ensure adequate sleep opportunity before the MSLT (the patient must have sufficient nocturnal sleep for valid MSLT interpretation) 1
• Identify any sleep-disordered breathing that would need to be treated before diagnosing a primary hypersomnia 3

Why Other Options Are Incorrect

Sleep diary followed by MSLT (option a) is inadequate because:

• While sleep diaries are useful assessment tools 1, they cannot replace the overnight PSG
• The PSG is necessary to exclude other sleep disorders and ensure adequate sleep before MSLT interpretation 1

Actigraphy followed by maintenance of wakefulness test (option b) is inappropriate because:

• The MWT is indicated for assessing ability to remain awake in safety-sensitive situations or to assess treatment response, not for initial diagnosis 2
• The MWT is not a diagnostic test for narcolepsy or idiopathic hypersomnia 2

Split-night polysomnogram (option d) is incorrect because:

• Split-night studies are used for obstructive sleep apnea diagnosis and CPAP titration, not for evaluating hypersomnias of central origin
• This patient's presentation does not suggest sleep apnea (no snoring, apneas, or gasping mentioned)

Key Clinical Features Supporting This Diagnosis

This 23-year-old woman presents with classic features suggesting narcolepsy:

• Excessive daytime sleepiness despite adequate sleep duration (9 hours) 1
• Frequent unrefreshing naps (5-6 times daily) 1
• Sudden sleep attacks in dangerous situations (falling asleep at red light), which represents a significant safety concern 1
• Narcolepsy should be considered when excessive sleepiness is accompanied by frequent short naps 1

Important Caveats

The MSLT cannot be used in isolation to confirm or exclude narcolepsy and is most valuable when interpreted in conjunction with clinical findings. 4 The sensitivity of the combination of ≥2 sleep onset REM periods with mean sleep latency <5 minutes is only 70%, with specificity of 97%. 4

The MSLT is not routinely indicated for initial evaluation of obstructive sleep apnea, insomnia, or circadian rhythm disorders. 2 This emphasizes the importance of the clinical presentation matching a suspected hypersomnia of central origin before ordering this test.