Case 2: An 12-year-old girl with recurrent sleep attacks

A healthy 12-year-old girl presented with episodes of fatigue recurring for more than one year. Fatigue was followed by sleep onset and typically developed in the afternoon during quiet moments. Episodes had occurred while she was in class, talking or even shopping, but could be avoided if she was participating in stimulating activities. She also reported sporadic tonus losses without any falls, which occurred when she experienced strong emotions. She reported sleeping an average of 11 h per night and napping for 1 h during the day. Her parents had recently separated, which had caused sadness, but she still had good relationships with both parents as well as her siblings. She enjoyed school, studied well and did not report any conflicts with friends or teachers, nor was she overwhelmed by any concerns. She reported no infectious contacts, weight or appetite changes, constipation, polyuria or neurological symptoms. An initial evaluation by electroencephalography revealed few irritative elements, and cerebral magnetic resonance imaging showed no significant anomalies. Thyroid-stimulating hormone and hemoglobin A1c levels were normal. Polysomnography (PSG) revealed agitated sleep with short-latency rapid eye movement (REM) sleep after awakening, and several spontaneous micro-awakenings. No signs of obstructive sleep apnea were observed. A diagnosis of narcolepsy was made on the basis of the clinical history and typical features on PSG. Narcolepsy is defined by excessive daytime sleepiness with or without cataplexy, the latter being characterized by conscious, sudden physical collapse typically in response to strong emotions. Afflicted patients also complain of fatigue, hallucinations and sleep paralysis. Because of such atypical symptoms, diagnosis may be delayed by several years. It typically presents during childhood and among young adults, with a prevalence of approximately 0.05% in the Western population. The condition is believed to originate from the destruction of hypocretin-secreting neurons in the hypothalamus. Hypocretin, also referred as orexin, is a neurotransmitter directly associated with wakefulness. Research has shown that narcolepsy is linked with one human leukocyte antigen (HLA) haplotype (DBQB1*0602) for most affected individuals. Symptom severity supports an immune-based explanation of the condition, increasing in a linear manner with allele number and the presence of specific antibodies toward hypocretin-secreting neurons. More recently, infectious triggers of the condition were validated during the swine flu pandemic in China – with fourfold greater identification of narcolepsy/cataplexy among nonvaccinated children – and vast increments of narcolepsy/cataplexy diagnoses in Swedish and Finnish youth exposed to a certain type of flu vaccine (1). Because narcolepsy and cataplexy in paediatric populations present with nonspecific symptoms, it is important to consider such rare diagnoses while performing complete primary evaluation for common pathologies. Along with testing for anemia, dysthyroidism, infections and metabolic illnesses, a thorough mental examination is indicated to rule out mood disorders. Rare illnesses, such as Kleine-Levin syndrome, must be considered because they have similar clinical presentations. The International Classification of Sleep Disorders has established precise criteria for the diagnosis of narcolepsy with or without cataplexy. While patient history is important, nocturnal PSG is key to the diagnosis because it also allows the exclusion of primary sleep disorders such as obstructive sleep apnea. A multiple sleep latency test (MSLT), consisting of five 20 min naps to monitor daytime sleepiness, should be performed the next day. Typical findings consist of limited REM sleep latency (premature apparition of a REM sleep phase linked to loss of muscle tone and dreaming). When available, confirmatory testing by PSG/MSLT is preferred for narcolepsy with cataplexy or, alternatively, decreased orexin level on lumbar puncture. In contrast, confirmatory testing is essential for narcolepsy without cataplexy. Finally, HLA haplotype may also be tested, but is currently not recommended as a routine diagnostic evaluation because it lacks specificity (1). Therapy is oriented toward relieving patient symptoms rather than treating the underlying condition. Patients should avoid irregular sleep patterns because they exacerbate symptoms, and schedule daytime naps when possible. Because there are no specific guidelines concerning pharmacological therapy for children, paediatricians still rely on treatments proven to be effective in adults. It is, therefore, common practice to begin with modafinil (1). Although its mechanism of action is not fully understood, this alpha-adrenergic agonist with wake-promoting effects is taken early in the morning. It is sometimes preferred to psychostimulants for adults because it has lower potential for abuse and rebound hypersomnia. Medications, such as tricyclic antidepressants and selective serotonin reuptake inhibitors, reduce REM sleep as side effects, thus lowering the number of cataplexy attacks. Sodium oxybate is the only drug found to be effective against all symptoms; however, its availability is limited because it is a sodium salt of γ-hydroxybutyrate, and illicit use has adverse effects on the central nervous system. Studies show that the condition has serious social and educational repercussions. Children afflicted by narcolepsy present with a high incidence of behavioural and mood disorders, which directly interfere with their social skills/abilities. Moreover, excessive daytime sleepiness leads to higher absenteeism rates, which, consequently, generate educational difficulties (2). Retrospectively, our patient presented with typical narcolepsy with cataplexy symptoms. Along with sleep studies, she was positive for HLA haplotype DBQB1*0602. Based on local experience, she was first started on low-dose long-acting lys-dexamphetamine, with near-complete resolution of her complaints. Narcolepsy/cataplexy is a rare disorder among children, and has a probable immunological basis. Early diagnosis of narcolepsy/cataplexy is possible through clinician awareness, mostly of clinical symptoms, with specific adjunct evaluations. Sleep hygiene and appropriate medication may allow children afflicted with the condition to develop to their full potential. The authors thank Ovid Da Silva for his help in the preparation of the manuscript, and Drs Pierre G Tremblay and Marianne Deschênes for their valuable clinical input.

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