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    • The different sleep duration in children their

    2018-10-26

    The different sleep duration in children, their reactions and difficulty in verbalizing their symptoms make it even more difficult to recognize and value the clinical data at these ages. Excessive sleepiness might be interpreted as a physiological need of napping in a small child, and in turn as a manifestation of laziness in older children. In addition to the excessive sleepiness, memory lapses, concentration problems and automatic behaviors, especially during monotonous activities, are also associated and can result in learning disabilities at school age [1,2,5,12,13]. Repeated difficulty in achieving expected or desired levels of performance might lead to irritability, hyperactivity, aggressiveness or even depression [2]. The hypnagogic or hypnopompic hallucinations sometimes associated with sleep paralysis, might be scary to the child, leading to resistance in going to sleep or be interpreted as nightmares or night terrors. Cataplexy is a sudden and reversible reduction in muscle tone, commonly triggered by a stimulus such as laughter, surprise or fright. It may lead to falls, which in small children may not be taken into consideration and/or be misinterpreted as a simple clumsy gait, or lead to differential diagnosis with atonic convulsive crisis [2,14] or cardiovascular syncope. In children, cataplexy might be limited to facial muscles, giving rise to an apathetic face, open mouth and protruding tongue, with a slow and slurred speech. Other symptoms that may be associated are obesity and early puberty [13,15]. The weight increase might be related to nocturnal sleep disturbance and consequent change of the feeding pattern [16,17], or with the fact that hypocretin deficiency may have a direct effect on myeloperoxidase and lower the basal metabolic needs [5]. The lack of symptom specificity and the other mentioned difficulties make diagnosis of narcolepsy in children a real challenge. Sometimes other diagnosis such as attention deficit hyperactivity disorder, epilepsy, behavioral insomnia, depression or other psychiatric disturbance may be evoked. Therefore, diagnosis may suffer significant delays and it is often only achieved in adolescence or early adulthood. Delays of 10–15 years between clinical presentation and diagnostic confirmation have been described [1,6]. In the pediatric population and in cases of sudden onset or less characteristic evolution, it is important to exclude secondary causes of narcolepsy. These may amount up to 25%, with genetic syndromes and hereditary metabolic diseases being the most predominant causes [10]. In these cases, the symptoms appear at an early age and associated with the underlying pathology [1,6,18]. Cataplexy is highly selective and almost pathognomonic of narcolepsy, but it also constitutes one of the symptoms to be considered in some genetic diseases, such as Niemann-Pick type 3, Norrie and Prader-Willi syndromes, myotonic dystrophy type 1, or in CNS trauma and tumors [2,10]. In narcolepsy, cataplexy often appears months or years after EDS; if it appears isolated or at an early age, the hypothesis of hypothalamic lesion must be considered [2]. The diagnosis is based on the results of polygraphic sleep study (PSG) and on the multiple sleep latency test (MSLT). However, in children, caution should be taken in MSLT interpretation due to the difficulty in establishing the lower age limit for application of the diagnostic criteria. Previously, the lower age limit has been established at 8 years age [6,11], but recent studies point to the possibility of its application since 5 years of age in cases with a strong suspicion of narcolepsy [19]. The MSLT is considered positive if the average sleep latency is less than 8min and if there is presence of at least 2 sleep onset rapid eye movement periods (SOREMPs) [19]. PSG must be made the night before the MSLT in order to exclude the existence of another pathology, such as an obstructive sleep apnea syndrome, which might justify the EDS. HLA DQB1*06:02 is the marker with highest specificity for narcolepsy in all ethnic groups [3], and this relation is particularly strong in the cases where cataplexy is present [3]. This allele is present in 90% of the narcolepsy cases, but it is also present in 12–38% of people without the disease [3,11].