KLS is a rare disorder characterized by recurrent episodic hypersomnia. Other associated symptoms include various behavioral and cognitive disturbances [2]. Male-to-female ratio is about 3:1 [1]. Females are often older at presentation than males [9]. This a noteworthy case because of not only the rarity of KLS especially in young females, but also having an infrequent narcolepsy-like pattern, two SOREMs and decreased sleep-onset latency in MSLT. The large number of cases is reported to be sporadic, as our patient [3, 10].
In 75% of cases, KLS onset occurred during the second decade or earlier [11]. The age at KLS onset is reported to be 16.9 ± 8.5 years (median: 15 years, range: 4–82 years) [1, 10, 12,13,14].
This syndrome is often missed, and there could be delays in diagnosis up to 2.5 years [5, 8], like diagnostic delay of our case. The patient was 20 years old when she was referred to us, but the onset of her KLS was at 14 years of age. She had frequent episodes of hypersomnolence and cognitive dysfunction for 6 years, and had history of taking fluoxetine, ritalin and lithium with no improvement. Our patient presented with hypersomnia and cognitive dysfunction but did not report eating disorder (anorexia or hyperphagia) or disinhibited behavior (such as hypersexuality). Almost all patients have symptoms of hypersomnia and cognitive disturbances such as confusion, concentration, attention and memory defects, while 66–75% had hyperphagia and 50–53% had sexual disinhibition [1, 9, 11].
Episodes of KLS present with an average of 19 episodes (median: 7 episodes, range: 2–130 episodes, mean ± SD: 12 ± 15 episodes). The episodes last between 2 and 80 days (sleep duration ranges: 15–24 h per day, median: 10 days, mean: 12 ± 9 days). Inter episode duration ranges from 0.5 to 72 months (median: 3.5 months, mean: 6 ± 10 months). The median duration of primary KLS is 8 years. The mean age at the end of KLS is reported to be 23 ± 12 years [2, 11, 15,16,17,18,19,20]. Our patient had almost 65 episodes, which lasted for 7 days. The range of inter-episode duration was 20–25 days. Between episodes she was totally normal, such as 96.4% patients. In a few cases, patients reported academic decline and a mild, long-lasting memory dysfunction between episodes [1, 15, 21, 22]. Her hypersomnolence episodes decreased gradually in frequency, duration, and intensity prior to termination and terminated with total and spontaneous recovery [1, 23].
KLS has been categorized into mild, moderate, and severe forms [10]. Accordingly, our patient can be categorized as moderate form. In the moderate form of KLS, patients have more frequent episodes, about 1 per month lasting 7 to 10 days; alternatively, patients experience fewer episodes (2 or 3) per year but the episodes are prolonged (lasting 3–6 months) [10, 24].
While several triggers have been reported to be associated with the initial episodes of hypersomnolence in KLS (61% of patients), there are no known causal links [1].
The most frequent factor was an infection at the disease onset (a flu-like illness or a non-specific fever) in more than two-thirds of the patients, other triggers have been reported, such as alcohol consumption, head trauma or sleep deprivation, already stressed by some authors, seems associated with onset of KLS [1, 3, 15, 17, 25,26,27,28]. The initial episode of our patient hypersomnolence was associated with a severe emotional stress.
Her EEG had suspicious spike and wave in PSG at one of episodes, however, further evaluation by neurologic revealed normal pattern of EEG. Her EEG was done in wakefulness and was normal. Completely normal EEG findings are seen in only about 30% of patients with KLS. In 70% of the patients, a non-specific diffuse slowing of background EEG activity, such as the alpha frequency band being slowed toward 7–8 Hz, was observed. Low-frequency, high-amplitude waves also occur [1, 10, 29]. Rarely, isolated spike discharges, self-limited photo-paroxysmal response or sharp waves are observed, but are considered of no clinical significance [1, 15, 30, 31].
In her PSG, sleep-onset latency was 12 min; total sleep time was 573 min (Stage 1, 10%; Stage 2, 61%; Stage 3–4, 19.8%; REM sleep, 9.2%), accordingly sleep efficiency was 90%. The patients had 8 REM periods. REM latency was 1:11 min. In other reports, mean total sleep time was 445 ± 122 min during the night (Stage 1, 6 ± 4%; Stage 2, 56 ± 9%; Stage 3–4, 19 ± 11%; REM sleep, 19 ± 6%) during an episode [1, 32, 33]. Rapid eye movement (REM) sleep as a percentage of total sleep time is greater during attacks compared to asymptomatic periods. There was increased total sleep time, but decreased sleep efficiency and frequent awakenings from sleep stage N2 [10, 32]. REM sleep is commonly reported during daytime sleep recordings or multiple sleep latency tests (mean sleep latency: 3 ± 1.1 min). Consistent with our patient, in one report, 21% had a narcolepsy-like pattern (≥ 2 sleep onset in REM periods) [1, 32, 33].
In MSLT, She reported sleep in three of four naps. Patient had two sleep-onset rapid eye movements (SOREMs) in four naps and her mean sleep-onset latency was 7 min. In two other reports, adolescents with KLS demonstrated the MSLT criteria for narcolepsy (MSL < 8 min, and 2 ≤ SOREM episodes) during the symptomatic period [34, 35] compared to when they were asymptomatic [10]. The overall mean sleep latency at MSLT was 9.51 ± 4.82 min in other researches [36,37,38,39].
Here, we reported a rare case of KLS in a young patient who had a periodic hypersomnolence pattern with a narcolepsy-like pattern in her MSLT without commonly reported behavioral characteristics of KLS in previous reports. The paper highlights attention of sleep medicine specialists towards patients’ reported symptoms and sleep pattern throughout the time instead of sticking to objective criteria such as MSLT that could be misleading as in this patient.
