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Objectives The aim of this study was to investigate the influence of age on the manifestation of narcolepsy symptoms and cognitive difficulties in patients with narcolepsy. Methods A total of 321 participants were included in the study: 157 were patients with narcolepsy from two Sleep Disorders Clinics and 164 were control participants. Narcoleptic patients were evaluated and diagnosed at the Sleep Disorders Clinic. All participants were interviewed by telephone using the Sleep-EVAL System. The interview comprised, among else, a detailed evaluation of narcolepsy symptoms and of cognitive difficulties. Results The first manifestation of the disease appeared early in life for most narcoleptic patients: 54.1% had their first symptom before the age of 20 years. Daytime sleepiness was the first symptom to appear in 65.5% of cases. In narcoleptics 60 years or older, cataplexy was more likely to be the first symptom to appear (47.4%) compared with other narcoleptic patients (21.4%; P<.05). Reported cognitive difficulties (attention–concentration, praxis, delay recall, orientation for persons, temporal orientation, and prospective memory) were higher in narcoleptic patients compared with the controls. The severity of daytime sleepiness and the presence of a major depressive disorder partly explained the cognitive difficulties. However, attention–concentration deficits and difficulties in prospective memory remained significant. Age was unrelated to cognitive difficulties in narcoleptics patients. Conclusions The first manifestation of narcolepsy appears early in life. Reported cognitive difficulties are important in narcoleptic patients and are only partly explained by age, severity of daytime sleepiness, and major depressive disorder.

Narcolepsy is a rare neurological disorder affecting less than 0.05% of the general population [1] and [2], although Japanese population surveys found higher rates [3] and [4]. Earlier reports from cohort and clinical studies [5] and [6] were already signaling the scarcity of this affection. This disease is characterized by daytime sleep attacks and manifestations of various REM sleep abnormalities (cataplexy, sleep paralysis, and hypnagogic hallucinations). Unfortunately, few studies have investigated the influence of age on the characteristics of narcolepsy, perhaps because this disorder is usually diagnosed late in the life of the patient. A recent study was underlying a fact: In half of the cases, narcolepsy was recognized after the age of 40 years [7]. At the level of clinical, polysomnographic, and multiple sleep latency test (MSLT) assessments, although most of the studies did not find significant changes with age [7] and [8], a recent study reported a decrease with age in the number of sleep-onset REM periods and an increase in the mean sleep latency on the MSLT [9]. Studies that investigated memory and attention in participants with narcolepsy had mixed results. Some studies that examined the level of sleepiness in relationship with cognitive performance in healthy participants found that sleepiness has an impact on memory [10], while others found that memory function remained intact [11] and [12]. Some studies reported that up to half of narcoleptic patients complained of memory problems [13] and [14], while other studies found that narcoleptics did not differ from normal participants on memory tasks [15] and [16]. Studies assessing the performance of narcoleptics on attention tasks found, on one hand, that there was little or no impairment in the ability to sustain attention [15] and [17], while, on the other hand, others demonstrated a clear deficit in vigilance and attention [18] and [19]. Moreover, the cognitive impairment related to age was not clearly identified in those patients. This issue could be of importance in determining the real impact due to the disease on cognitive functions. This disabling disorder has a deep impact on psychosocial functioning of the patients [20] and [21]. In fact, age and narcolepsy in its expressivity has not yet been thoroughly investigated. Consequently, this study aims to answer the following questions: (1) what are the first manifestations of the disease as reported by the patients? At what age did they appear? (2) What are the current clinical symptoms? Are they the same at different ages? (3) What are the specific sleep characteristics of narcoleptic patients by age categories? (4) What is the impact of narcolepsy on cognitive functions? Are these cognitive impairments related to age?

The characteristics of the participants are presented in Table 1. The narcoleptic group included a greater proportion of men than did the control group. It also had a smaller proportion of married individuals and of retired individuals compared with the control group. The BMI of the narcoleptic group was also higher than the one of the control group, even after controlling for age and gender. Table 1. Demographic characteristics of patients with narcolepsy and control group Narcolepsy (n=157) Control (n=164) % Males 68.8⁎ 44.5 Age (mean±S.D.) 46.6 (18.7)⁎ 54.7 (13.7) % Married 51.6⁎ 100 Occupation (%) Working 57.3 45.2 Not working 20.4 18.3 Retired 22.3⁎ 36.6 BMI (mean±S.D.) 26.7 (5.0)⁎ 24.7 (4.2) ⁎ P<.001 between groups. Table options Narcolepsy-cataplexy represented 75% of the narcoleptic group. A total of 24.4% of narcoleptic participants were taking a medication for this sleep disorder. First manifestations of narcolepsy Fig. 1 presents the age at the first appearance of symptoms among the narcoleptic patients. As it can be observed, a peak of frequency is observed between 15 and 19 years of age for daytime sleepiness and cataplexy. A second peak is observed between 20 and 24 years for sleep paralysis and hypnagogic hallucinations. Full-size image (45 K) Fig. 1. Age at the appearance of first manifestations of narcolepsy symptoms. Figure options Narcoleptics younger than 45 years of age were more likely to report the following: (1) Excessive daytime sleepiness (EDS) first appeared during childhood or adolescence (50.8%) than narcoleptics between 45 ad 59 years (19.5%) and 60 years or older (26.5%; P<.05). (2) The first episode of cataplexy occurred during childhood or adolescence (44.7%) than narcoleptics 60 years or older (12.8%; P<.001). Time-sequence of symptoms Overall, participants reported that the first symptom of narcolepsy appeared before age of 12 years in 12.3% of cases, between 13 and 20 years in 41.8% of cases, between 21 and 30 years in 24.6% of cases, and after the age of 30 years in 21.3% of cases. There was no significant difference between the three age groups of narcoleptic patients. Daytime sleepiness, occurring alone or concomitantly with other narcolepsy symptoms, was the first manifestation of disease in 65.5% of cases. In 52.5% of narcolepsy with cataplexy, the first episode of cataplexy appeared closely to first symptoms of EDS. In 29.5% of cases, cataplexy was reported to have occurred before daytime sleepiness, and in 18.0% of cases, EDS appeared before cataplexy. Elderly narcoleptic patients (≥60 years old) were more likely to report that cataplexy occurred before EDS (47.4%) than did other narcoleptics (21.4%; P<.05). Narcoleptic patients reported that episodes of sleep paralysis occurred approximately in the same time than EDS in 52.9% of cases and sleep paralysis occurred after daytime sleepiness in 44.1% of cases.