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Sleep-Related Breathing Disorders (SRBD): Clinical Presentations and Diagnostic Approaches

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CLASSIFICATION (ICSD-3)

1. Obstructive Sleep Apnea (OSA) - adult and pediatric
2. Central Sleep Apneas (CSA) - including Cheyne-Stokes breathing
3. Sleep-Related Hypoventilation Disorders - including Obesity Hypoventilation Syndrome (OHS)
4. Sleep-Related Hypoxemia Disorder

• Isolated symptoms/variants: snoring, catathrenia

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PART I: CLINICAL PRESENTATIONS

A. Obstructive Sleep Apnea-Hypopnea (OSAH)

• Male sex, middle age, obesity (most common)
• Anatomical: micrognathia, retrognathia, nasopharyngeal abnormalities, enlarged tonsils/adenoids
• Metabolic/endocrine: hypothyroidism, acromegaly

• Hypertension (~60%), type 2 diabetes (~33%), coronary artery disease (~28%)
• Heart failure (~14%), stroke/TIA (~6%)
• Depression, anxiety, PTSD (significantly elevated psychiatric comorbidity)
• Polycythemia, memory impairment

• Snoring, mouth breathing, adenotonsillar hypertrophy
• Behavioral problems, hyperactivity, poor school performance (may mimic ADHD)
• Growth failure, neurobehavioral deficits

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B. Central Sleep Apnea (CSA)

• Cyclical waxing and waning (crescendo-decrescendo) respiratory effort
• Separated by central apneas or hypopneas
• Common in CHF, stroke; associated with daytime hypersomnolence, insomnia

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C. Sleep-Related Hypoventilation Disorders

1. Obesity Hypoventilation Syndrome (OHS / Pickwickian Syndrome)
   • BMI >30 + awake PaCO₂ >45 mmHg + no other cause
   • Symptoms: EDS, dyspnea, cor pulmonale in advanced cases
   • Often coexists with OSA (~90%)
2. Congenital Central Alveolar Hypoventilation Syndrome (Ondine's Curse)
   • PHOX2B gene mutation
   • Loss of automatic breathing control during sleep; voluntary breathing preserved
   • Presents in neonates with cyanosis, respiratory failure during sleep
3. Late-onset Central Hypoventilation with Hypothalamic Dysfunction
   • Childhood onset; associated with obesity, hypothalamic tumors (craniopharyngioma)
4. Idiopathic Central Alveolar Hypoventilation
   • Diagnosis of exclusion; normal pulmonary function, no structural lesion
5. Medication/Substance-related Hypoventilation
   • Opioids, benzodiazepines, sedative-hypnotics
6. Medical Disorder-related Hypoventilation
   • COPD, neuromuscular diseases (ALS, myasthenia gravis), kyphoscoliosis, chest wall disorders

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D. Upper Airway Resistance Syndrome (UARS)

• Repeated abnormal respiratory efforts without frank apnea
• Crescendo snoring + arousals (Respiratory Effort-Related Arousals - RERAs)
• Respiratory Disturbance Index (RDI) elevated; AHI may be normal
• Presents with EDS, unrefreshing sleep, fatigue

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E. Sleep-Related Hypoxemia

• SpO₂ <88% for ≥5 minutes during sleep without frank apnea/hypoventilation
• Seen in COPD, pulmonary fibrosis, heart failure

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PART II: DIAGNOSTIC APPROACHES

Step 1: Clinical History and Questionnaires

• STOP-BANG Questionnaire: Snoring, Tiredness, Observed apneas, high blood Pressure, BMI >35, Age >50, Neck circumference >40 cm, Gender (male). Score ≥3 = high risk for moderate-severe OSA
• Epworth Sleepiness Scale (ESS): Score ≥10 suggests clinically significant EDS (scored 0-3 for 8 situations; total /24)
• Berlin Questionnaire: Validated for OSA risk stratification in primary care
• Detailed sleep history: snoring, witnessed apneas, nocturia, headaches, cognitive complaints
• Bed partner interview (witnessed events are diagnostically important)

Step 2: Physical Examination

• BMI, neck circumference (>40 cm in women, >43 cm in men)
• Oropharyngeal assessment: Mallampati score, tonsillar hypertrophy, retrognathia, macroglossia
• Nasal patency (deviated septum, polyps)
• Cardiovascular: hypertension, signs of cor pulmonale (right heart failure)
• Neurological assessment if CSA suspected

Step 3: Objective Sleep Testing

A. In-Laboratory Polysomnography (PSG) - Gold Standard

• EEG (3+ channels) - sleep staging
• EOG (electro-oculogram) - REM identification
• EMG (chin/submental, tibialis) - muscle tone, limb movements
• Oronasal thermistor + nasal pressure sensor - airflow
• Chest and abdominal bands (inductive plethysmography) - respiratory effort
• Pulse oximetry (SpO₂)
• ECG - arrhythmia detection
• Audio/video recording

• Mild: 5-14 events/hour
• Moderate: 15-30 events/hour
• Severe: >30 events/hour

B. Home Sleep Apnea Testing (HSAT) / Out-of-Center Sleep Testing (OCST)

• Type III portable monitors (most commonly used): Record airflow, respiratory effort, SpO₂, heart rate - without EEG
• Type IV monitors: Single/2-channel (oximetry only) - screening only

• High pretest probability of moderate-severe OSA
• No significant comorbidities (no CHF, severe COPD, neuromuscular disease)
• No suspicion of other sleep disorders (parasomnias, narcolepsy)
• When in-laboratory PSG is not feasible

• AHI based on recording time (not sleep time) → underestimates severity
• Cannot detect RERAs (no EEG)
• Reduced sensitivity for mild OSA
• If HSAT negative but clinical suspicion high → proceed to in-lab PSG

C. Overnight Pulse Oximetry

• Screening tool: "sawtooth pattern" of recurrent desaturations suggests OSA
• Not sufficient alone for diagnosis; high false-negative rate
• Useful for monitoring treatment response

D. Additional Diagnostic Tests

• Arterial Blood Gas (ABG): Essential in suspected hypoventilation (PaCO₂ >45 mmHg awake = OHS when unexplained)
• Multiple Sleep Latency Test (MSLT): Rules out narcolepsy as cause of EDS; mean sleep latency <8 min with ≥2 SOREMPs = narcolepsy
• Maintenance of Wakefulness Test (MWT): Assesses ability to remain awake; used in safety-critical occupations
• Serum bicarbonate: Elevated HCO₃⁻ (>27 mEq/L) suggests chronic CO₂ retention; useful OHS screening marker
• Thyroid function tests: Rule out hypothyroidism in OSA/hypoventilation
• Echocardiography: Assess for pulmonary hypertension, right ventricular dysfunction (cor pulmonale)
• Lateral cephalometry/CT of upper airway: Anatomical assessment pre-surgery
• Drug/genetic testing: PHOX2B mutation testing in suspected congenital central alveolar hypoventilation

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DIAGNOSTIC ALGORITHM SUMMARY

Clinical suspicion (snoring + EDS + obesity/witnessed apneas)
        ↓
History + ESS + STOP-BANG
        ↓
High pretest probability + no comorbidities → HSAT (Type III)
Low probability / comorbidities / CSA suspected → In-lab PSG
        ↓
HSAT negative but clinically suspected → Repeat HSAT or PSG
        ↓
AHI ≥5 (with symptoms) or ≥15 (without) → OSA confirmed
ABG + Serum HCO₃ raised → Evaluate for OHS/hypoventilation
Absent respiratory effort on PSG → CSA workup (Echo, brain MRI, medications review)

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KEY DISTINGUISHING POINTS (Exam-Oriented)

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• Kaplan & Sadock's Comprehensive Textbook of Psychiatry, Ch. 23
• Kaplan and Sadock's Synopsis of Psychiatry, Ch. 15
• Fishman's Pulmonary Diseases and Disorders, Ch. 98
• Bradley and Daroff's Neurology in Clinical Practice, Ch. 101
• Goldman-Cecil Medicine, Ch. 374