Narcolepsy and hypersomnolence — branching viva

Opening — framing the problem

The examiner begins: a ten-year-old has three months of irresistible daytime sleepiness and, when he laughs hard, his knees buckle and his head drops while he stays fully aware. Talk me through your reasoning. [1] [2]

I would frame this as narcolepsy type 1 until proven otherwise, because the pairing of new, irresistible daytime sleepiness with emotion-triggered loss of muscle tone and preserved consciousness is the clinical signature of cataplexy, which is nearly specific for narcolepsy type 1. The rapid weight gain points to the hypothalamic involvement seen in paediatric narcolepsy. [2] [7]

Branch A — the mechanism

Why does he lose muscle tone when he laughs, and what is the underlying lesion? [4]

Cataplexy is the muscle atonia of REM sleep released into wakefulness by strong emotion. The underlying lesion is loss of the orexin, or hypocretin, neurons in the lateral hypothalamus, which normally stabilise wakefulness and hold REM sleep in place; without orexin, the boundary between wake and REM breaks down, producing sleepiness, cataplexy, sleep paralysis and hypnagogic hallucinations. The loss is thought to be autoimmune on an HLA-DQB1*06:02 background. [4] [6]

Branch B — confirming the diagnosis

How would you confirm this, and what would you expect to find? [3]

I would arrange overnight polysomnography to exclude another cause and confirm adequate sleep, followed by a multiple sleep latency test the next day, expecting a mean sleep latency at or below eight minutes and two or more sleep-onset REM periods. Where the picture is doubtful, a low cerebrospinal fluid orexin level, at or below 110 picograms per millilitre, confirms narcolepsy type 1. I would ensure he is off REM-suppressing drugs first and interpret the numbers against his age. [3] [10]

Branch C — management

The diagnosis is confirmed. How will you treat him? [1]

I would start with the non-drug foundation of sleep hygiene and planned short daytime naps, plus school accommodations, safety advice and psychological support. For the sleepiness I would use a wake-promoting agent such as modafinil first line, with pitolisant, methylphenidate or solriamfetol as alternatives. For the cataplexy I would use sodium oxybate, which also improves sleepiness and night sleep, or a REM-suppressing antidepressant such as venlafaxine, tapering rather than stopping it abruptly. [12] [13]

Branch D — the pivot without cataplexy

Now an adolescent presents with excessive daytime sleepiness but no cataplexy at all. Does that change things? [1]

Without cataplexy I cannot assume narcolepsy type 1, and I must widen the differential to narcolepsy type 2, idiopathic hypersomnia and, most importantly, secondary sleepiness from insufficient sleep, obstructive sleep apnoea, delayed sleep phase, medication or depression. I would exclude these first, then use polysomnography and the multiple sleep latency test, remembering that type 2 is a diagnosis of exclusion that must be reviewed over time. [3] [1]

Closing — the safety rule

Give me the single safety point you would emphasise to this family. [9]

Cataplexy and severe sleepiness create injury risk, so I would advise supervision around water, roads and heights and, in due course, careful attention to driving; and I would warn never to stop an anticataplectic antidepressant abruptly, because sudden withdrawal can precipitate rebound cataplexy or status cataplecticus. [9] [3]