Sleep, fatigue and circadian disorders in adolescents — branching viva

Stem

The examiner will test whether you understand adolescent sleep physiology well enough to separate the common mechanisms, distinguish sleepiness from fatigue, build a stepped-care plan, and recognise the red flags that mandate referral. [10]

Branch 1 — Physiology

Examiner: Why do adolescents sleep less than children? [8]

Strong answer: Two biological changes combine. The circadian phase delays by about one to two hours at puberty — the dim-light melatonin onset moves later, tied to pubertal stage rather than age — so sleep onset shifts later. At the same time, the social clock does not move: school starts early, so wake-time is fixed. Sleep is squeezed from both ends, producing chronic partial sleep deprivation. The "perfect storm" framing captures the added effects of evening screens (which delay melatonin further) and adolescent autonomy over bedtime. [8] [10]

Examiner: Explain the two-process model. [8]

Strong answer: Borbély's two-process model has Process S — homeostatic sleep pressure that builds while awake and dissipates in sleep — and Process C — the circadian alerting signal that gates sleep through the day and withdraws at night. We fall asleep when rising Process S meets a falling circadian alerting signal. In adolescence both processes shift later: the circadian signal withdraws later in the evening, and homeostatic pressure may accumulate more slowly, so the brain is genuinely alert later and sleepier for longer into the morning. [8]

Branch 2 — The differential of the tired teenager

Examiner: A 14-year-old is "always tired". How do you frame the differential? [11]

Strong answer: First, separate sleepiness (a tendency to doze, pointing to a sleep problem) from fatigue (low energy without dozing, pointing to mood or medical causes). For sleepiness, the three mechanisms are insufficient sleep (not enough opportunity), insomnia (enough opportunity but cannot sleep), and circadian timing disorders such as delayed sleep-wake phase disorder. I then add the rarer but serious causes: central disorders of hypersomnolence (narcolepsy, idiopathic hypersomnia) and obstructive sleep apnoea. For fatigue without dozing, I screen for depression and anxiety, and consider iron deficiency, hypothyroidism, post-viral fatigue, coeliac disease, an eating disorder or chronic disease. [11]

Examiner: How do you tell insufficient sleep from insomnia from delayed phase? [9]

Strong answer: With a two-week sleep diary. Insufficient sleep: short opportunity, but the young person sleeps well when given the chance, with a large weekday–weekend gap. Insomnia: adequate opportunity (nine hours in bed) but a long sleep latency, frequent waking, conditioned anxiety about sleep, and daytime "wired-tired" fatigue. Delayed sleep-wake phase disorder: completely normal, refreshing sleep at a delayed clock time, with marked weekend rebound — the discriminating question is what they do on a free weekend. [9] [10]

Branch 3 — Delayed sleep-wake phase disorder

Examiner: A 15-year-old sleeps 02:00 to 11:00 whenever allowed and cannot get up for school. How do you manage her? [7]

Strong answer: Combine a phase-advance plan: a consistent rise time held seven days a week (the clock's anchor); bright light for 30 to 60 minutes on waking; and low-dose melatonin taken about three to five hours before her current habitual sleep onset, gradually moved earlier with the schedule, with the caveat that paediatric use is off-label in many regions and warrants specialist input. I protect against evening light and screens, and use a sleep diary to monitor progress, reviewing at four to eight weeks. [7] [15]

Examiner: Why not just prescribe melatonin and leave it? [15]

Strong answer: Because melatonin phase-shifts a delayed clock — it is not a general sedative for insomnia or for simple insufficient sleep. Without a fixed rise time and morning light, melatonin alone often fails; without evening-light protection the clock can delay further. A recent meta-analysis confirms it helps sleep parameters in young people, but it works as part of a package, not in isolation. [15]

Branch 4 — Insomnia

Examiner: A 16-year-old lies awake two hours every night and is anxious about sleep. First-line? [13]

Strong answer: Cognitive-behavioural therapy for insomnia (CBT-I), not a hypnotic. The components are stimulus control (bed is for sleep; leave the bed if awake for more than 20 minutes), sleep restriction (temporarily reduce time in bed to consolidate sleep), cognitive therapy for the unhelpful beliefs driving arousal, sleep hygiene, and relapse prevention. The SENSE trial and related work show durable improvement in adolescent sleep and mood; chronic hypnotic use is to be avoided. [13]

Examiner: When would you involve mental-health services? [11]

Strong answer: Whenever insomnia sits alongside depression, anxiety or self-harm risk — which is common, because sleep and mood reinforce each other. I screen mood and safety at every sleep visit, and if there is active suicidal ideation or severe functional decline, mental-health assessment and safety planning take priority over the sleep diary. [11]

Branch 5 — The red-flag stem

Examiner: A 17-year-old sleeps nine sound hours but dozes in afternoon classes; last week his legs buckled when he laughed. What is this? [16]

Strong answer: This is narcolepsy type 1 — daily irresistible sleepiness despite adequate overnight sleep, with cataplexy (emotion-triggered bilateral loss of muscle tone), caused by loss of hypothalamic orexin neurons. It is a red flag. I would refer urgently to a sleep specialist for an overnight polysomnogram followed by a multiple sleep latency test, performed after documented adequate sleep and withdrawal of REM-suppressing medication. I would counsel on drowsy-driving safety and support education and mood while awaiting confirmation. Stimulant and sodium oxybate therapy is specialist-led. [16]

Examiner: Name two other red flags in adolescent sleep. [16]

Strong answer: Loud habitual snoring with witnessed apnoea, especially in an obese adolescent — obstructive sleep apnoea, confirmed with polysomnography. And a tired teenager with anhedonia, hopelessness or any self-harm — a hidden mood crisis, which is a mental-health emergency. [11] [16]

Examiner extras

• Adolescents need 8 to 10 hours of sleep; most get less on school nights because biological onset is delayed while wake-time is fixed. [4]
• The single most discriminating question is what they do on a free weekend. [9]
• Later school start times (08:30 or later) are AAP-endorsed and improve sleep, mood, attendance and driving safety. [10]
• Polysomnography is reserved for suspected OSA and before an MSLT — not for straightforward behavioural problems. [16]