2.2 Major Sleep Disorders

Why Disorder Recognition Is Tested

Quick Answer: The exam expects you to pair a clinical presentation with the correct polysomnographic (PSG) finding. The single highest-yield skill is distinguishing obstructive from central events (effort present vs. absent), and recognizing the multiple sleep latency test (MSLT) pattern of narcolepsy versus the loss of REM atonia in REM sleep behavior disorder.

Disorders are organized into sleep-disordered breathing, movement disorders, central disorders of hypersomnolence, parasomnias, insomnia and circadian rhythm sleep-wake disorders. The technologist's role is to acquire a clean signal, recognize patterns in real time, and document them so the interpreting physician can diagnose - never to diagnose independently (see section 2.3).

Sleep-Disordered Breathing

The AASM defines the two core respiratory events the technologist scores:

• An apnea is a >=90% drop in airflow for >=10 seconds, classified obstructive (effort continues), central (effort absent) or mixed (central onset, obstructive end).

• A hypopnea is a >=30% drop in airflow for >=10 seconds accompanied by a >=3% oxygen desaturation and/or an arousal (the recommended AASM rule).

• Obstructive sleep apnea (OSA): Repetitive upper-airway collapse. The hallmark is airflow cessation with continued or increased thoracoabdominal effort, usually ending in an arousal and desaturation. Severity uses the apnea-hypopnea index (AHI) - events per hour of sleep: 5-14 mild, 15-29 moderate, >=30 severe. Typical presentation: loud snoring, witnessed apneas, daytime sleepiness, obesity, large neck circumference, hypertension.

• Central sleep apnea (CSA): Airflow cessation without respiratory effort because the brainstem fails to drive breathing. Cheyne-Stokes breathing - a crescendo-decrescendo pattern with central apneas at the troughs - is classic in congestive heart failure and stroke. Treatment-emergent (complex) CSA can appear when positive airway pressure is started for OSA.

• Sleep-related hypoventilation: Sustained elevation of carbon dioxide (CO2) rather than discrete apneas, producing prolonged desaturation. It requires CO2 monitoring (end-tidal capnography or transcutaneous CO2). Common in obesity hypoventilation syndrome and neuromuscular disease.

Worked example: repeated 15-second airflow stops, chest and abdomen still moving, each ending with a 4% desaturation and an arousal - score these as obstructive apneas, and the running event count drives the AHI. If chest and abdomen are flat during the stops, score central.

Movement Disorders

• Periodic limb movement disorder (PLMD): Repetitive, stereotyped limb movements during sleep scored on the anterior tibialis EMG (each 0.5-10 s, in runs of >=4 separated by 5-90 s) as a periodic limb movement index. PLMD is diagnosed only when the movements cause sleep disturbance and are not better explained by another disorder such as OSA.
• Restless legs syndrome (RLS): A clinical, awake diagnosis - an urge to move the legs, worse at rest and in the evening, relieved by movement. RLS is strongly associated with periodic limb movements of sleep and with low iron/ferritin, so iron studies are part of the workup.

Central Disorders of Hypersomnolence

• Narcolepsy: Excessive daytime sleepiness; type 1 includes cataplexy (sudden emotion-triggered loss of muscle tone) and low cerebrospinal-fluid hypocretin/orexin. The diagnostic MSLT is performed the day after an adequate overnight PSG and shows a mean sleep latency <=8 minutes with >=2 sleep-onset REM periods (SOREMPs); a SOREMP on the preceding overnight PSG can count as one of the two.
• Idiopathic hypersomnia: Excessive sleepiness with a short MSLT latency but <2 SOREMPs, distinguishing it from narcolepsy.

Parasomnias, Insomnia and Circadian Disorders

• NREM parasomnias (sleepwalking, sleep terrors, confusional arousals) arise out of N3 in the first third of the night; the patient typically has no memory of the event and is hard to fully waken. They are most common in children, consistent with the robust N3 of that age group.
• REM sleep behavior disorder (RBD): Loss of the normal chin/limb atonia of REM, allowing dream enactment (kicking, punching, falling out of bed). It occurs in the last third of the night, affects older adults, and can precede neurodegenerative disease (Parkinson disease, dementia with Lewy bodies). PSG shows increased EMG tone during REM.
• Chronic insomnia disorder: Difficulty initiating or maintaining sleep with daytime impairment >=3 nights/week for >=3 months; it is a clinical diagnosis and PSG is not routinely required unless another disorder is suspected.
• Circadian rhythm sleep-wake disorders: Misalignment of the internal clock and the desired schedule - delayed sleep-wake phase (common in adolescents), advanced sleep-wake phase (common in older adults), shift-work disorder and jet lag. They are evaluated with sleep logs and actigraphy over days to weeks, not a single-night PSG.

Clinical Presentation vs. PSG Finding

Common traps the exam exploits:

• Effort is the discriminator between obstructive and central apnea - desaturation occurs in both, so do not use desaturation alone to classify the event.
• RLS is diagnosed awake from the patient's history; periodic limb movements on PSG support but do not by themselves make the RLS diagnosis.
• Hypoventilation is about sustained CO2, not discrete 10-second events, so the AHI can be deceptively low while the patient is profoundly hypoxemic.
• NREM parasomnias arise from deep N3 early; RBD arises from REM late - timing in the night and the atonia status separate them.