Upper Airway Resistance Syndrome (UARS)

Upper airway resistance syndrome (UARS) is a clinical entity within the spectrum of sleep-disordered breathing (SDB), first described by Christian Guilleminault and colleagues in 1993 to characterize patients with sleep fragmentation and daytime symptoms but without the meeting traditional definitions of obstructive sleep apnea (OSA). UARS is characterized by repetitive episodes of partial upper airway narrowing causing increased respiratory effort (negative pleural pressure swings) without sufficient flow limitation to meet criteria for apnea (90% reduction in airflow for 10+ seconds) or hypopnea (30% reduction in airflow with 4% oxygen desaturation OR 50% reduction with arousal — variable definitions). However, the increased respiratory effort eventually triggers arousal from sleep (respiratory effort-related arousal, RERA), leading to sleep fragmentation, increased sympathetic activity, and daytime symptoms. The pathophysiology involves a combination of anatomic predisposition (narrow upper airway, narrow high-arched palate, mandibular retrognathia, long face, narrow nasal passages, nasal obstruction) and physiologic factors (increased pharyngeal collapsibility, decreased pharyngeal muscle tone during sleep, particularly REM sleep). The relationship between UARS, snoring, OSA, and central sleep apnea is debated — some authors consider UARS as part of the OSA spectrum, others as distinct entity with different demographics, symptoms, and pathophysiology. The 2014 AASM scoring rules officially incorporated RERAs and broadened hypopnea definition (3% desaturation or arousal), reducing prevalence of UARS as distinct entity in clinical practice.

Demographics and clinical presentation: UARS patients tend to be different from classical OSA patients — typically younger (mean age 30-40 years), leaner (BMI often less than 25-30), with greater female predominance (1:1 or female-predominant in some series, vs 2-3:1 male predominance in OSA), and often with craniofacial features predisposing to upper airway narrowing (narrow palate, mandibular retrognathia, long-face syndrome, narrow nasal passages, large tongue). Symptoms often differ from OSA: while excessive daytime sleepiness is common, UARS patients are more likely to have INSOMNIA (paradoxically — difficulty maintaining sleep, with frequent awakenings or perceived poor sleep quality), profound fatigue often disproportionate to sleepiness, frequent morning headaches, depression and anxiety (often misdiagnosed as primary psychiatric disorder), decreased concentration, memory difficulties, and decreased academic or work performance. Autonomic symptoms are notable: orthostatic intolerance, dizziness, cold extremities, peripheral vasoconstriction, low blood pressure, irritable bowel syndrome, chronic fatigue. Snoring is often but not always present (UARS can occur in non-snorers). Loud crescendo snoring as in OSA is less common. Witnessed apneas are rare. The combination of insomnia, fatigue, headache, and depression in a young thin patient with subtle craniofacial features and possible mild snoring should prompt consideration of UARS. Differential diagnosis: chronic fatigue syndrome, fibromyalgia, depression, narcolepsy, idiopathic hypersomnia, primary insomnia, postural orthostatic tachycardia syndrome (POTS), and chronic primary headache disorders.

Diagnosis: full attended polysomnography (PSG) is required, ideally with measures sensitive enough to detect RERAs. Gold standard for RERA detection: esophageal pressure manometry (Pes) — measures intrathoracic pressure swings, with progressive crescendo of negative pressure followed by arousal indicating RERA. Esophageal manometry is uncomfortable, technically demanding, and not widely available, limiting clinical use. Alternative methods now standard: nasal pressure transducer with simultaneous airflow signals (sensitive to flow limitation pattern of inspiratory flow flattening), with arousals scored on EEG. Per 2014 AASM scoring rules: a respiratory event is scored as RERA if there is sequence of breaths lasting at least 10 seconds with crescendo of respiratory effort or flattening of inspiratory flow that does not meet hypopnea criteria, but ends in arousal. Respiratory disturbance index (RDI) = (apneas + hypopneas + RERAs) / hour of sleep. UARS diagnosis: AHI less than 5 events/hour but RDI greater than 5/hour (or RERA index greater than 10/hour) with characteristic clinical symptoms. Other useful PSG features: increased fragmentation index, decreased sleep efficiency, decreased deep sleep stages (N3), decreased REM sleep, alpha intrusion in NREM sleep (alpha-delta sleep, may explain non-restorative sleep). Workup also includes: thorough sleep history (Berlin Questionnaire, STOP-BANG, Epworth Sleepiness Scale, insomnia severity index), upper airway examination (nasal obstruction, septum deviation, turbinate hypertrophy, narrow palate, retrognathia, large tongue, Friedman tongue position III/IV, modified Mallampati score III/IV, dental occlusion), thyroid function tests, complete blood count, ferritin and iron studies (restless legs association), screening for depression and anxiety. Treatment: similar to mild OSA. (1) Continuous positive airway pressure (CPAP) is the most effective treatment, with auto-titrating or fixed pressures typically lower than for OSA (5-8 cm H2O often sufficient). Adherence may be challenging in UARS as patients often less aware of breathing problems. (2) Oral appliances (mandibular advancement devices, MADs) are very effective for UARS, often preferred by patients due to comfort and portability — referral to dental sleep specialist for custom fitting. (3) Positional therapy (avoid supine sleep) for positional UARS. (4) Weight management for overweight patients. (5) Treatment of nasal obstruction is critical: septoplasty for septal deviation, turbinate reduction (radiofrequency, microdebrider), nasal valve repair, nasal corticosteroids for allergic rhinitis, nasal dilators. (6) Surgical airway expansion for selected patients with anatomic abnormalities: uvulopalatopharyngoplasty (UPPP, less effective for UARS), expansion sphincter pharyngoplasty, lateral pharyngoplasty, tonsillectomy, base of tongue surgery, hypoglossal nerve stimulation (rarely indicated for UARS), maxillomandibular advancement (most effective surgical option, especially for craniofacial UARS in younger patients). (7) Treatment of comorbid insomnia with cognitive behavioral therapy for insomnia (CBT-I), as treating SDB without addressing insomnia component may not fully resolve symptoms. (8) Treatment of associated depression and anxiety. Long-term follow-up: untreated UARS may progress to OSA over years (particularly with weight gain, aging, hormonal changes such as menopause). Quality of life improves significantly with effective treatment. Symptoms of fatigue, headache, and concentration often resolve within weeks of effective therapy.