What is the appropriate workup for a 16-year-old female with a past history of anorexia nervosa (in remission) and currently taking Prozac (fluoxetine) 40 mg daily, who presents with a one-year history of excessive daytime sleepiness and episodes of falling asleep in class despite adequate nocturnal sleep?

Workup for Excessive Daytime Sleepiness in an Adolescent on Fluoxetine

This 16-year-old requires immediate evaluation for medication-induced sleepiness from fluoxetine, followed by systematic assessment for primary sleep disorders including obstructive sleep apnea and narcolepsy, using polysomnography and multiple sleep latency testing if initial evaluation suggests a central hypersomnia disorder.

Immediate Medication Assessment

Fluoxetine is a known contributor to excessive daytime sleepiness and should be your first consideration. SSRIs, including fluoxetine, are specifically listed as antidepressants that can cause significant daytime sedation and are recognized as insomnia-contributing medications that derange restorative sleep 1, 2. The 40 mg daily dose is substantial for an adolescent.

Key Actions:

• Consider switching fluoxetine administration to bedtime to convert the sedating side effect into a therapeutic sleep benefit, rather than causing daytime dysfunction 2
• If sleepiness persists, consider switching to a less sedating antidepressant or one that doesn't worsen sleep architecture 2
• Document the temporal relationship between fluoxetine initiation/dose increases and onset of sleepiness symptoms

Comprehensive Sleep History

Obtain detailed information addressing specific elements that distinguish between sleep disorders 1:

Critical Questions:

• Cataplexy symptoms: sudden muscle weakness triggered by emotions (laughing, surprise) 1
• Sleep paralysis: inability to move when falling asleep or waking 1
• Hypnagogic hallucinations: vivid dreams or hallucinations at sleep onset 1
• Automatic behaviors: performing tasks without awareness 1
• Nap characteristics: duration, frequency, whether they are refreshing, and if dreaming occurs during naps 1
• Snoring or witnessed apneas: screen for obstructive sleep apnea 1
• Leg discomfort at night: assess for restless legs syndrome 1
• Actual nocturnal sleep duration: verify "adequate sleep" claim with sleep diary 1

Physical Examination

Perform a targeted examination focusing on 1:

• Upper airway assessment: tonsillar hypertrophy, retrognathia, neck circumference
• Neurologic examination: to identify any central nervous system pathology
• Cognitive assessment: document baseline cognitive function for monitoring

Objective Sleep Assessment Tools

Validated Questionnaires:

• Epworth Sleepiness Scale (ESS): most commonly used screening tool; score ≥10 indicates pathological sleepiness 1
• Sleep diary: 1-2 weeks to document actual sleep-wake patterns 1

Laboratory Workup

Order the following tests to exclude metabolic and endocrine causes 1:

• Thyroid stimulating hormone (TSH)
• Complete blood count (CBC)
• Comprehensive metabolic panel (CMP)
• Liver function tests (LFTs)
• Ferritin level: if any symptoms of restless legs; levels <45-50 ng/mL indicate treatable RLS 1

Sleep Study Indications

If the ESS score is ≥10 and medication adjustment doesn't resolve symptoms, proceed with polysomnography (PSG) followed by multiple sleep latency testing (MSLT). 1

Polysomnography (Overnight):

• Rules out obstructive sleep apnea (must be excluded before diagnosing primary hypersomnia) 1
• Identifies periodic limb movements
• Documents sleep architecture disruption
• Required prerequisite before MSLT 1

Multiple Sleep Latency Test (MSLT):

Perform the day following PSG if overnight study doesn't explain sleepiness 1:

• Consists of 4-5 daytime naps at 2-hour intervals 1
• Mean sleep latency ≤8 minutes indicates pathological sleepiness 1
• ≥2 sleep-onset REM periods (SOREMPs) with mean sleep latency ≤8 minutes is diagnostic of narcolepsy 1

Differential Diagnosis Priority

Given this patient's profile, consider in order:

1. Medication-induced sleepiness from fluoxetine (most likely) 1, 2
2. Insufficient sleep syndrome: verify actual sleep duration despite patient's report 3, 4
3. Narcolepsy: especially if cataplexy, sleep paralysis, or hypnagogic hallucinations present 1, 5
4. Idiopathic hypersomnia: if MSLT shows sleepiness without SOREMPs 5, 3
5. Obstructive sleep apnea: less common in adolescent females but must be excluded 1
6. Depression-related hypersomnia: though she's on treatment, depression can cause prolonged sleep 1

Critical Pitfalls to Avoid

• Do not assume all sleepiness is depression-related without excluding primary sleep disorders 2
• Do not add sedating medications (benzodiazepines, zolpidem) to treat presumed insomnia when the patient has excessive daytime sleepiness 1, 2
• Do not diagnose narcolepsy or idiopathic hypersomnia without first performing PSG to exclude sleep apnea 1
• Recognize that feelings of fatigue are more common than true sleepiness in psychiatric conditions; significant sleepiness (actually falling asleep involuntarily) should prompt evaluation for primary sleep disorders 1

Special Considerations for This Patient

Anorexia History:

• Metabolic disturbances from past malnutrition may contribute to sleep disruption 6
• Verify current nutritional status and weight stability
• Consider that fluoxetine, while sometimes used in anorexia maintenance, may have different side effect profiles in patients with eating disorder history 7

Adolescent-Specific Factors:

• Narcolepsy commonly presents in adolescence, with peak onset in the teenage years 5, 3
• Delayed sleep phase syndrome is common in adolescents but wouldn't cause sleepiness with "adequate" nocturnal sleep
• School performance impact (falling asleep in class) represents significant functional impairment requiring urgent evaluation

When to Refer to Sleep Specialist

Refer if 1, 2:

• ESS score ≥10 persists after medication adjustment
• Clinical suspicion for narcolepsy (presence of auxiliary symptoms)
• Cause of sleepiness remains unknown after initial workup
• Patient requires PSG/MSLT for diagnosis