Case Presentation

A 51-year-old non-smoker, a professional driver by occupation, presented with excessive daytime sleepiness for the last three years. He had episodes of falling asleep while driving and had sustained motor vehicular accidents twice due to sleepiness.

There was history suggestive of insomnia, disturbed sleep, morning headaches, bizarre dreams, hypnagogic hallucinations and restless leg syndrome. He also gave a history suggestive of sudden loss of muscle power causing loss of posture and falls, with preserved consciousness and awareness of the event, without headache, sensory disturbance or any other neurological symptoms.

He reported occasional snoring, but no choking episodes or witnessed apnoeas. He was a known asthmatic with allergic rhinitis on treatment, with no other medical comorbidities.

Examination and Baseline Investigations

His BMI was 19.8. Spirometry revealed moderate obstruction. He had mild iron deficiency anaemia with haemoglobin 10.7 g/dL. Iron studies showed serum iron 40 mcg/dL, total iron binding capacity 277 mcg/dL and serum ferritin 13 ng/mL. CT brain was normal. The Epworth Sleepiness Scale score was 17.

Polysomnography (PSG)

Although the PSG revealed a low sleep efficiency with no REM sleep, it ruled out obstructive sleep apnoea. It also documented a strikingly high burden of periodic limb movements.

Table 1 · Sleep architecture and respiratory parameters

Table 2 · Limb movement parameters

Multiple Sleep Latency Test (MSLT)

His MSLT revealed a mean sleep latency of 1 minute 15 seconds with four sleep onset REM periods (SOREMs).

Table 3 · MSLT nap data

Diagnosis and Management

Based on the PSG and MSLT findings together with a positive history of cataplexy, a diagnosis of narcolepsy with cataplexy (type 1 narcolepsy) with restless leg syndrome was made.

The patient's asthma treatment was optimized. He was educated about good sleep hygiene and avoidance of medications which impair daytime alertness and nocturnal sleep, and was advised daytime scheduled naps. He was treated with modafinil and methylphenidate for excessive daytime sleepiness, and supplemental iron for restless leg syndrome.

The patient improved in terms of daytime alertness and performance. He has not experienced any further episodes of cataplexy.

Discussion

Excessive Daytime Sleepiness

Excessive daytime sleepiness (EDS) is defined as difficulty staying awake and alert, or an increased desire to sleep during the day. EDS can result in decreased work performance, increased risk of car and work accidents, impaired emotional regulation, impaired quality of life, and social and relationship problems.

Various differential diagnoses need to be considered while evaluating EDS. Insufficient sleep syndrome is the most common cause and can be due to environmental factors, shift work or an irregular schedule. Other sleep disorders such as circadian rhythm disorders, obstructive sleep apnoea, restless leg syndrome (RLS), idiopathic hypersomnolence and narcolepsy also present with EDS. Certain medical conditions, psychiatric illness, substance abuse and drugs are additional causes.

Narcolepsy: The Clinical Syndrome

Narcolepsy is a clinical syndrome of daytime sleepiness, cataplexy, hypnagogic hallucinations, sleep paralysis and occasionally automatic behaviours. Cataplexy is a sudden loss of muscle control, typically on both sides of the body, triggered by strong emotions.

The cardinal symptom of daytime sleepiness occurs in every patient, whereas cataplexy, hypnagogic hallucinations and sleep paralysis have been reported in approximately 70%, 25% and 5% of patients respectively. Narcolepsy with cataplexy is caused by a severe loss of the neurons that produce the orexin (hypocretin) neuropeptides, through an autoimmune mechanism.

The Role of the MSLT

The MSLT is essential for the diagnosis of narcolepsy. It is a validated, objective measure of the tendency to fall asleep, indicated in the evaluation of suspected narcolepsy, and may have utility in differentiating idiopathic hypersomnolence from narcolepsy.

• Consists of five nap opportunities, each of 20 minutes duration, performed at 2-hour intervals.
• Begins within 1.5 to 3 hours after termination of the nocturnal recording (PSG).
• The mean sleep latency and the number of sleep onset REM periods (SOREMs) are the diagnostically useful outputs.

The diagnostic criteria for narcolepsy are described in the International Classification of Sleep Disorders (ICSD)-3 guidelines. As per the guidelines, a mean sleep latency of ≤ 8 minutes with two or more SOREMs on an MSLT is diagnostic of narcolepsy, provided other causes of EDS are ruled out.

Type 1 versus Type 2 Narcolepsy

Narcolepsy is divided into two types. If the patient has cataplexy, or a cerebrospinal fluid (CSF) hypocretin-1 concentration < 110 pg/mL or < 1/3 of the mean value obtained in normal subjects, it is called type 1 narcolepsy or narcolepsy-cataplexy.

Narcolepsy-cataplexy is known to be associated with several other sleep disorders such as parasomnias, obstructive sleep apnoea, and restless leg syndrome / periodic limb movement disorder (PLMS) — as illustrated by the marked PLMS burden in this case.

Treatment

Modafinil is the first-line therapy in the treatment of EDS in narcolepsy. In addition, non-pharmacological interventions consist of scheduled naps, good sleep hygiene and avoidance of drugs that can worsen daytime sleepiness. The second-line therapy for daytime sleepiness is methylphenidate. Sodium oxybate and venlafaxine are indicated for cataplexy.

Conclusion

Narcolepsy should be considered while evaluating EDS after ruling out commoner causes such as insufficient sleep and OSA. Cataplexy is strongly suggestive of narcolepsy. The MSLT is a very important investigative modality for diagnosing narcolepsy and for ruling out other conditions.