ORIGINAL ARTICLE

Demographic, clinical, and polysomnographic features in patientswith narcolepsy: an experience of 181 patients with narcolepsyfrom a Turkish sleep center

Murat Erdem • Oguzhan Oz • Adem Balikci •

Mehmet Yucel • Mustafa Alper • Hakan Akgun •

Fuat Ozgen

Received: 1 March 2011 / Accepted: 13 February 2012 / Published online: 2 March 2012

� Belgian Neurological Society 2012

Abstract The present study was designed to describe the

socio-demographic, clinical, and polysomnographic features

of patients diagnosed with narcolepsy in our sleep center. This

retrospective cross-sectional study was conducted on 181

patients diagnosed with narcolepsy based on the results of

clinical evaluation, polysomnography (PSG), and multiple

sleep latency test (MSLT) between 1993 and 2009. Approx-

imately 70% of the patients had cataplexy, whereas 42% had

hallucinations and 55.8% had sleep paralysis. Although

sleep efficiency was higher (91.28 ± 5.89%) in patients

with narcolepsy, they woke frequently during the night, and

their percentages of deep sleep were low (stage 3, 5.12 ±

3.08%, stage 4, 9.60 ± 7.10%). Our study group was divided

into two based on age: individuals aged\30 years (n = 152)

and [30 years (n = 29). REM latency on PSG was shorter

(t = 2.96, p = 0.004) and sleep onset REM (SOREM) on

MSLT was higher (t = 2.56, p = 0.011) in the older group

than in the younger group. Cataplexy is seen in most patients

with narcolepsy. In older patients, REM latency on PSG

is shorter and the number of SOREM on MSLT is higher.

Introduction

Narcolepsy is characterized by irresistible attacks of sleep

under unusual circumstances (for example, while eating,

driving the car, or talking), hypnagogic (vivid) hallucinations

on falling asleep or on waking (hypnopompic hallucinations),

cataplexy (a sudden, usually bilateral loss of muscle tone

provoked by emotional stimuli and which can make the person

fall), sleep paralysis (unpleasant generalized paralysis just

before sleep, while falling asleep, or on waking), and disturbed

nocturnal sleep [1]. The first clinical description of narcolepsy

in the medical literature can be attributed to Sir Thomas

Willis. Yoss and Daly published their criteria for diagnosis of

the narcoleptic syndrome, with a description of the classic

‘‘narcoleptic tetrad’’ comprising the four main symptoms of

narcolepsy: excessive daytime sleepiness, cataplexy, sleep

paralysis, and hypnagogic/hypnopompic hallucinations [2]. In

the next period, biological indicators of narcolepsy were

defined. Vogel has shown the presence of sleep onset rapid eye

movement (SOREM) in these cases, and Honda et al. have

revealed the association of Class II HLA-DR2 antigens with

the disease in 1983 [3]. In studies conducted in the last decade,

cerebrospinal fluid (CSF) hypocretin levels were found to be

lower in more than 90% of the patients with narcolepsy than in

healthy individuals [4–6]. The prevalence of the disease is

around 1/2,000 [7, 8]. The disease is also more common in

men. Typically, narcolepsy starts in the twenties; however,

cases of narcolepsy onset in early childhood or after the age of

60 years have also been reported [6, 9].

In this study, archived patient records from Turkey’s

first sleep disorder center were scanned and examined to

determine socio-demographic, clinical, and polysomno-

graphic features of patients diagnosed with narcolepsy; the

results are discussed in light of the current literature.

Methods

This retrospective study was conducted in the Sleep

Research Center at Gulhane Military Medical Hospital

M. Erdem (&) � A. Balikci � M. Alper � F. Ozgen

Department of Psychiatry, Gulhane Military Medical Academy,

General Tevfik Saglam Street No: 1, 06018 Etlik,

Ankara, Turkey

e-mail: drmerdem@yahoo.com

O. Oz � M. Yucel � H. Akgun

Department of Neurology, Gulhane Military Medical Academy,

Etlik, Turkey

123

Acta Neurol Belg (2012) 112:177–181

DOI 10.1007/s13760-012-0053-x

(GMMH), Ankara, Turkey. Most patients admitted to our

center were diagnosed before they enlisted in military

service. To assess whether individuals are fit for military

service, they are evaluated for sleep-related abnormalities.

The results of assessment are then used to determine

qualification for military service. Civilian patients were

also admitted to our center but were present in lower

numbers. Socio-demographic and clinical characteristics

and results of polysomnography (PSG) and multiple sleep

latency test (MSLT) were evaluated at the Sleep Research

Center of the GMMH for 181 patients who were diagnosed

with narcolepsy on the basis of clinical evaluation, PSG,

and MSLT between March 1993 and December 2009.

Patients with abnormal findings in complete blood

count; routine biochemical tests, including kidney and liver

function tests and sedimentation rate; thyroid function

tests; and vitamin B12 levels were excluded from the

study. Patients using sedatives (e.g., benzodiazepines) and

sleep-deprived patients (i.e., sleeping less than 7 h per 24 h

based on sleep diary records) were also excluded. All

patients were evaluated by a psychiatrist to rule out psy-

chiatric disorders. In addition, a neurologist examined the

patients to rule out neurological disorders. Those with

restless legs syndrome (RLS) and obstructive sleep apnea

syndrome (OSAS) were also excluded from the study.

Subjective sleepiness was assessed using the Epsworth

Sleepiness Scale (ESS). The ESS is a specialized, validated

sleep questionnaire containing eight items that ask for self-

reported disclosure of the expectation of dozing in various

situations. The validity and reliability studies of the

Turkish form of the ESS were done by Izci et al. [10].

GRASS Model 78-type analog and Somnostar Alpha Sleep

PSG were used for obtaining sleep records. Consecutive

PSG and MSLT studies were performed on all patients

during diagnosis. Electroencephalogram (EEG), electro-

oculogram (EOG), submental electromyography (EMG),

and electrocardiogram (ECG) data were obtained from

PSG records. With the aim of achieving differential diag-

nosis, during PSG recording, a nasal thermistor was used

for timing respiration, and during EMG recording, leg

electrodes were attached at pre-tibial muscles for assessing

periodic leg movements. Records were scored in 30 second

epochs according to the international criteria [11]. Fol-

lowing PSG, standard MSLTs were performed in accor-

dance with the American Academy of Sleep Medicine

guidelines [12]. Manual analysis of the MSLT data inclu-

ded sleep latency from lights out to first epoch of sleep,

mean latencies to sleep for all naps, and number of

SOREM periods. Four tests (naps) 2 h apart were

performed beginning 2 h after awakening in the morning.

Routine hook-up was carried out after omitting leg EMG

and cardio-respiratory parameters. Sleep was defined as

three consecutive epochs of stage 1 sleep or one epoch of

any other stage of sleep. The test continued for 15 min

after sleep onset to document the presence or absence of

REM sleep. Sleep latency was averaged over all naps and

recorded on the report form. Continuous variables are

given as mean ± standard deviation, and discrete variables

are reported as numbers and percentages in the statistical

analysis.

Results

Men constituted 91.2% of the patients. The high rate of

male patients admitted to our center may be associated

with characteristics of the patient population. The mean

age of patients was 24.61 ± 6.83 years. Of 181 patients,

cataplexy was detected in 126 (69.6%), hallucinations in 76

(42%), and sleep paralysis in 101 patients (55.8%). On an

average, the disease started at the age of 16 years and was

diagnosed approximately 8 years after onset of symptoms.

Socio-demographic and clinical characteristics of all sub-

jects are shown in Table 1.

Polysomnography results showed that the mean sleep

latency and sleep index were 4.68 ± 5.56 min and

91.28 ± 5.89%, respectively. The REM percentage was

16.69 ± 5.84, and REM latency was 24.16 ± 48.07 min.

On MSLT, the SOREM number was detected as

3.20 ± 0.79. PSG and MSLT results of patients are shown

in Table 2.

Our study group was then separated into two groups:

patients aged \30 years (n = 152) and [30 years

(n = 29). REM latency on PSG was shorter (t = 2.96,

p = 0.004) and SOREM on MSLT was higher (t = 2.56,

p = 0.011) in the older group than in the younger group.

Discussion

In this study, socio-demographic, clinical, and polysom-

nographic characteristics were evaluated in patients with

narcolepsy. In summary, the results of the study showed

that 70% of all patients experience cataplexy. Although the

incidence of hallucinations (42%) and sleep paralysis

(56%) was less than that of cataplexy, the incidence of

these two symptoms in the present study is higher than that

reported in the literature [2].

Clinical features

The clinical picture of narcolepsy consists of a tetrad of

symptoms: irresistible attacks of sleep, cataplexy, hypna-

gogic hallucinations, and sleep paralysis. In previous

studies, the proportion of patients with the narcolepsy tet-

rad was 10–27.7% [13]. In our study, the percentage of

178 Acta Neurol Belg (2012) 112:177–181

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patients with narcolepsy tetrad was 32.1%. The number of

symptoms increases over time in cases of narcolepsy [13].

In our study, patients’ mean age at onset was low

(16.10 ± 5.45 years); therefore, the high incidence of the

narcolepsy tetrad may be associated with the increase in

number of symptoms over time in patients receiving an

early diagnosis. In addition, genetic factors not assessed in

this study may also have played a role.

Similar to previous studies [8, 13], cataplexy was found

in 69.6% of our patients. Sleep paralysis was found in

55.8% of the cases. The incidence of sleep paralysis is

between 2.3 and 40% in the general population; in the form

of multiple episodes, it is between 1 and 10%. The rates of

sleep paralysis were found to be 17–66% in narcoleptic

patients [2]. This study evaluated only the presence of

sleep paralysis; however, it did not evaluate the duration

and frequency of sleep paralysis after the start of sleep and

whether sleep paralysis occurs during daytime sleep

attacks.

Hallucinations were observed in 42% of our cases. It has

been reported that the rate of hypnagogic-hypnopompic

hallucinations is 36% in healthy individuals [14] and

20–65% in narcoleptic cases [2, 3].

Interval between age at onset and initial diagnosis

In this study, age at onset was 16.10 ± 5.45 years; the disease

began before the age of 20 years in 68.2% of patients. Among

47 narcolepsy patients, Bahammam et al. [13] found that in

patients with cataplexy, age of onset was 20.5 years and that in

patients without cataplexy, it was 25.5 years. Ohayon et al.

[15] found that symptoms started before the age of 20 in

54.1% of 157 narcolepsy patients. The interval between

symptom onset and diagnosis was more than 8 years. Our

findings are consistent with the findings of Bahammam et al.

[13]. The reasons for delay in diagnosis include lack of

clinical knowledge about narcolepsy among physicians,

administration of symptomatic treatment without performing

a detailed clinical and polysomnographic evaluation, as well

as delay in seeking diagnosis by patients.

Epsworth sleepiness scale

The mean ESS score in patients was 18.60 ± 3.23 which is

consistent with the results of previous studies [3, 13]. The

ESS score was higher in patients with cataplexy than in

patients without cataplexy (t = 2.78, p = 0.06). This result

is consistent with that found in 520 patients with narco-

lepsy by Harsh et al. [16].

PSG and MSLT findings

Narcolepsy patients have a total sleep time (TST) similar to

that of controls but with reduced sleep efficiency, shortened

sleep latency, and shorter latency to the first REM episode.

Night time sleep in narcolepsy is highly fragmented and is

interrupted by numerous awakenings and larger amounts of

waking time after sleep onset. This leads to a lighter sleep,

with an increased amount of stage 1 sleep at the expense

mainly of stage 2 sleep, which is reduced. Slow wave sleep

(SWS) may be preserved or reduced, and the amount of

REM sleep is comparable to that in the normal population

[2, 17–20].

Table 1 Demographic and clinical characteristics of patients

Feature Number (%) Mean ± SD

Age – 24.61 ± 6.83

Education level (years) – 9.70 ± 3.62

Sex

Female 16 (8.8) –

Male 165 (91.2)

Age at onset – 16.10 ± 5.45

Disease duration – 8.47 ± 5.59

Body mass index (kg/m2) – 25.08 ± 3.62

Cataplexy

Yes 126 (69.6) –

No 55 (30.4)

Hallucination

Yes 76 (42.0) –

No 105 (58.0)

Sleep paralysis

Yes 101 (55.8) –

No 80 (44.2)

The number of episodes of sleep – 2.96 ± 1.28

Epworth Sleepiness Score – 18.60 ± 3.23

Table 2 PSG and MSLT results of patients

Mean ± SD Min–max

value

Total sleep time 546.08 ± 189.30 291–984

Sleep latency (min) 4.68 ± 5.56 0–26

Sleep index (%) 91.28 ± 5.89 65–99

Percentage of stage 0* 7.66–5.72 0–34

Percentage of stage 1 2.46 ± 3.36 0–22

Percentage of stage 2 58.18 ± 10.89 6–80

Percentage of stage 3 5.12 ± 3.08 0–13

Percentage of stage 4 9.60 ± 7.10 0–32

Percentage of REM 16.69 ± 5.84 5–35

REM latency (min) 24.16 ± 48.07 0–287

Number of wakefulness 16.30 ± 8.13 1–45

MSLT average sleep latency

(min)

2.84 ± 1.91 0.40–8

MSLT SOREM number 3.20 ± 0.79 1–4

Acta Neurol Belg (2012) 112:177–181 179

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Mean sleep latencies in narcoleptic patients are on aver-

age 3.1 ± 2.9 min [21]. In a study by Bahammam et al. [13]

the time required to fall asleep was 5.6 ± 1.1 min for

patients with cataplexy and 10.0 ± 2.6 min for patients

without cataplexy. In our study, the average sleep latency in

patients with narcolepsy was 4.68 ± 5.56 min.

According to the PSG findings in the present study of

patients with narcolepsy, sleep latency is short, sleep effi-

ciency is high, percentage of stage 2 sleep is high, rate of

slow wave sleep is low, REM latency is short, and the

number of bouts of wakefulness is high. Our findings are

consistent with some of the previous studies [16, 22, 23].

The presence of a REM period at the beginning of the

sleep is a significant feature of narcolepsy [24, 25].

SOREM is defined as the appearance of REM sleep within

15 min of the initiation of the recording. This occurs in

nearly 45% of narcolepsy patients [17, 18]. In our study,

the average REM latency was *24 min, and SOREM was

found in 74.6% of the cases. The reason for the higher

SOREM incidence compared with other studies may be the

lower mean age (24.6 years) of patients. In two separate

studies, the incidence of SOREM in young patients was

high and decreased with age [26, 27]. REM latency was

shorter and SOREM number on MSLT was higher in the

older age group than in the younger age group. MSLT is an

important tool in the diagnosis of narcolepsy and was

shown to be useful in distinguishing narcolepsy from idi-

opathic hypersomnolence [28].

Weaknesses of our study are that it is retrospective with

data collected over a long period, i.e. 16 years, and that

there is known inter-reader variability in sleep recording

analyses. With these reservations in mind, we believe that

the data from our cohort of 181 patients contribute to better

define the clinical and polysomnographic characteristics of

narcolepsy and the influence of age on them.

In summary, our findings in a large group of patients

diagnosed with definite narcolepsy according to demo-

graphic, clinical and polysomnographic features are largely

consistent with available data from the literature. The

nature and symptomatology of narcolepsy are insufficiently

known both by patients and physicians, which may delay

the diagnosis. Cataplexy is found in most narcolepsy

patients. In older patients, REM latency on PSG is shorter,

but the number of SOREM on MSLT is higher.

Conflict of interest None.

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