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Suspected OSAHS with false-negative respiratory polygraphy — SCE Respiratory MCQ

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HardObstructive Sleep ApnoeaSuspected OSAHS with false-negative respiratory polygraphySCE Respiratory

A 51-year-old woman is assessed for 18 months of sleep-maintenance insomnia, unrefreshing sleep, morning headaches and nocturia. Her partner reports loud snoring, recurrent breathing pauses and snorting arousals, particularly when she is supine. Her Epworth Sleepiness Scale score is 7/24. BMI is 32 kg/m² and examination shows a crowded oropharynx. Technically satisfactory home type III respiratory polygraphy records 8 hours 12 minutes and reports a respiratory event index of 4.3/hour. Recurrent inspiratory flow limitation and small desaturations cluster during a 2.5-hour period when her sleep diary indicates that she was asleep; she reports lying awake for much of the remaining recording. No central apnoeas are identified. Which investigation is the most appropriate next step?

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Correct answer: C — Perform full polysomnography with EEG-based sleep staging

Explanation lettering: B = shown as A · A = shown as B · E = shown as D · D = shown as E

Despite the formally negative respiratory event index, the pre-test probability of OSAHS remains high: she has multiple characteristic symptoms, witnessed obstructive events, obesity and upper-airway crowding. A low Epworth score does not exclude OSAHS, particularly in a patient presenting predominantly with insomnia and sleep fragmentation. Type III respiratory polygraphy lacks EEG sleep staging. Its event index is therefore generally calculated using recording or monitoring time rather than true sleep time. In this case, prolonged wakefulness has enlarged the denominator and may have materially underestimated event frequency. Limited-channel studies may also miss hypopnoeas associated with EEG arousal but little desaturation. NICE recommends considering polysomnography when respiratory polygraphy is negative but suggestive symptoms continue. Repeating the same modality (A) may reproduce the same denominator and arousal-scoring limitations. Oximetry (B) is less informative than the already completed polygraphy and may miss minimally desaturating obstructive events. Multiple sleep latency testing (D) evaluates objective hypersomnolence and is not the next diagnostic test for suspected OSAHS, especially with an Epworth score of 7. Drug-induced sleep endoscopy (E) may assist anatomical planning for selected surgical interventions after OSAHS is established, but it does not replace physiological diagnosis.

Reference: Obstructive sleep apnoea/hypopnoea syndrome and obesity hypoventilation syndrome in over 16s: section 1 (20 August 2021) — https://www.nice.org.uk/guidance/NG202/chapter/1-obstructive-sleep-apnoeahypopnoea-syndrome ERS technical standards for using type III devices (limited channel studies) in the diagnosis of sleep disordered breathing in adults and children (6 January 2023) — https://publications.ersnet.org/content/erj/61/1/2200422