What is the likely diagnosis and appropriate management for a 13‑year‑old with difficulty falling asleep, difficulty estimating elapsed time (time‑blindness), intense hyperfocus on specific interests, and no hyperactive symptoms?

Likely Diagnosis: ADHD Predominantly Inattentive Presentation with Comorbid Delayed Sleep-Wake Phase Disorder

This 13-year-old most likely has ADHD predominantly inattentive presentation (ADHD/I) with comorbid delayed sleep-wake phase disorder (DSWPD), and should be evaluated systematically using DSM-5 criteria with information from multiple settings before initiating treatment that addresses both conditions. 1

Diagnostic Evaluation

ADHD Assessment

The primary care clinician should determine that DSM-5 criteria are met, requiring at least 6 symptoms of inattention present for at least 6 months, with documented impairment in at least 2 settings (home, school, social), and symptoms present before age 12. 1

• Key inattentive symptoms to assess include: poor attention to details, difficulty sustaining attention, appearing preoccupied, difficulty completing tasks, organizational challenges, avoidance of tasks requiring sustained mental effort, losing things, easy distractibility, and forgetfulness 1
• The hyperfocus described is characteristic of ADHD—patients can paradoxically sustain intense attention on preferred activities while struggling with non-preferred tasks 1
• The absence of hyperactive symptoms suggests ADHD/I (314.00 [F90.0]) rather than combined or hyperactive-impulsive presentations 1
• Obtain information from parents/guardians, teachers, and other school personnel using standardized rating scales 1

Time Perception Deficits in ADHD

The "time blindness" described is a well-documented feature of ADHD:

• Children with ADHD demonstrate significant impairments in time discrimination, requiring intervals approximately 50 milliseconds longer to distinguish time differences compared to controls 2
• Time perception deficits are more pronounced in longer duration intervals and prospective tasks, consistent with deficient utilization of temporal information secondary to working memory and executive function deficits 3, 4
• This temporal processing deficit may impact language skills, motor timing, and the ability to estimate elapsed time 2

Sleep Disorder Assessment

DSWPD should be diagnosed when there is extreme difficulty falling asleep at typical bedtimes with difficulty waking at required times, but normal sleep quality when sleeping at delayed times, with symptoms present for at least 3 months and documented with sleep diaries for at least 7 days. 1

• DSWPD manifests as a delay of the major sleep episode with respect to desired timing or timing required for school and social demands 1
• Patients report extreme difficulty falling asleep at bedtimes considered typical among peers, but sleep quality is normal when allowed to sleep at delayed times 1
• Document sleep patterns with sleep diaries tracking bedtime, sleep latency, number of awakenings, wake after sleep onset, time in bed, total sleep time, and sleep efficiency 1

Rule Out Alternative Causes

Before confirming ADHD, systematically exclude:

• Anxiety disorders and depression, which can mimic inattention and are highly comorbid with ADHD 1, 5
• Sleep-disordered breathing or obstructive sleep apnea, which produce attention deficits resembling ADHD 5
• Medications that contribute to insomnia: SSRIs, stimulants (if already prescribed), decongestants, cardiovascular medications, or pulmonary medications 1
• Substance use, particularly caffeine, which can disrupt sleep and worsen attention 1

Management Algorithm

Step 1: Address Sleep First (Critical)

Begin with behavioral interventions for DSWPD before initiating ADHD medication, as stimulants will worsen insomnia and sleep must be stabilized first. 6

Behavioral Sleep Interventions (First-Line)

• Establish consistent bedtime routines with visual schedules to leverage preference for sameness and reduce anxiety about the sleep process 6, 7
• Apply bedtime fading: temporarily move bedtime later to match natural sleep onset (likely 11 PM-1 AM), then gradually shift earlier in 15-30 minute increments every 3-7 days 6, 7
• Implement strict sleep hygiene: consistent wake time (even weekends), limit screen time 1-2 hours before bed, dark/cool bedroom environment, avoid caffeine after noon 1
• Provide hands-on parent education about proper sleep-onset associations and consistent limit-setting 6, 7

Light Therapy and Melatonin (Second-Line)

• If behavioral interventions are insufficient after 4 weeks, add melatonin 1 mg given 30-60 minutes before desired bedtime, titrating up to maximum 6 mg based on response 6, 7
• Strategic morning bright light exposure (30-60 minutes upon waking) helps advance circadian phase in DSWPD 1
• Strategic avoidance of evening light exposure (blue light blocking glasses after 8 PM) prevents further phase delay 1

Monitoring Sleep Treatment

• Schedule follow-up within 2-4 weeks to assess progress using sleep diaries 6, 7
• Melatonin improves sleep-onset latency by approximately 39 minutes and total sleep duration by 44 minutes 6
• Treating sleep problems may improve daytime ADHD symptoms including inattention, impulsivity, and problematic behaviors 6

Step 2: Initiate ADHD Treatment (After Sleep Stabilization)

For Adolescents ≤70 kg

• Initiate atomoxetine (non-stimulant) at 0.5 mg/kg/day, increase after minimum 3 days to target dose of 1.2 mg/kg/day (maximum 1.4 mg/kg or 100 mg, whichever is less), administered as single morning dose or divided morning/late afternoon doses 8
• Atomoxetine is preferred initially because it does not worsen sleep and has lower abuse potential 8

For Adolescents >70 kg

• Initiate atomoxetine at 40 mg daily, increase after minimum 3 days to target dose of 80 mg, administered as single morning dose or divided doses 8

Alternative: Stimulant Therapy (Only After Sleep Stabilized)

• If atomoxetine is ineffective after adequate trial (6-8 weeks at target dose), consider stimulants (methylphenidate or amphetamine formulations) 5
• Critical: Do not start stimulants until sleep is stabilized, as they worsen insomnia 6
• Approximately 60% of patients show moderate-to-marked improvement with stimulants 5

Step 3: Monitor and Adjust

• Schedule follow-up every 2-4 weeks initially to assess treatment response, side effects, and functional outcomes in multiple settings 1, 5
• Use standardized rating scales from parents and teachers to objectively measure improvement 1
• Monitor for suicidal ideation, particularly in first weeks of atomoxetine treatment (0.4% risk vs 0% placebo) 8
• Screen for emerging comorbidities: depression (9% comorbidity), anxiety, substance use 5

Step 4: Referral Criteria

Refer to psychiatry or developmental-behavioral pediatrics if:

• Sleep problems persist despite behavioral interventions plus melatonin 6, 7
• ADHD symptoms persist despite adequate medication trial 1
• Complex comorbidity requiring specialized management (severe anxiety, depression, suspected bipolar disorder) 5
• Concern for alternative diagnoses (autism spectrum disorder, learning disabilities, psychotic disorders) 5
• Suspected primary sleep disorders (sleep apnea, periodic limb movements) 6

Critical Pitfalls to Avoid

• Never start ADHD stimulant medication before stabilizing sleep—this will worsen insomnia and create a vicious cycle 6
• Do not rely solely on self-report or parent report without obtaining teacher/school information from at least 2 settings 1
• Do not diagnose ADHD if symptoms are better explained by sleep deprivation alone—treat sleep first and reassess 1, 5
• Do not use benzodiazepines for sleep problems due to risk of disinhibition and behavioral side effects in adolescents 6, 7
• Do not implement behavioral sleep strategies without adequate parent education—success depends on proper implementation 6, 7
• Do not overlook that time blindness is a core feature of ADHD, not a separate diagnosis—it reflects deficient temporal information processing 2, 4
• Do not forget to document childhood onset before age 12 using collateral information (old report cards, teacher comments, parent recall) 1, 5