Obstructive Sleep Apnoea in MRCP: From STOP-BANG to Tirzepatide

Few respiratory topics weave together physiology, cardiology, endocrinology, ethics and law quite like obstructive sleep apnoea (OSA). MRCP examiners love it because a single stem can simultaneously test screening scores, sleep study interpretation, NICE-funded treatments, DVLA duties and — as of December 2024 — first-in-class pharmacotherapy. This guide condenses everything you need, structured the way an examiner actually thinks.

Why OSA Deserves Dedicated Revision Time

• Part 1: SBA stems built around Epworth scores, STOP-BANG interpretation, AHI severity grading and the classic comorbidity associations (resistant hypertension, AF, acromegaly).

• Part 2 Written: overnight oximetry traces, arterial blood gases in obesity-hypoventilation syndrome (OHS), and treatment selection based on AHI.

• PACES: the sleepy patient appears in Station 2 (history) or Station 5 (consultation) — and unprompted mention of driving regulations is a guaranteed mark.

Core Definitions You Must Nail

AHI severity grading — memorise these numbers:

Pathophysiology in Exam Language

The pharynx collapses when the negative intraluminal pressure generated during inspiration exceeds the stabilising force of the pharyngeal dilator muscles, particularly genioglossus. If asked in a viva why not everyone with a narrow airway has OSA, cite the four interacting traits:

1. Anatomical narrowing — obesity, macroglossia, retrognathia, nasal obstruction

2. High loop gain — intrinsically unstable ventilatory control (overshoot–undershoot cycling)

3. Low arousal threshold — micro-arousals occur before the airway restabilises, fragmenting sleep

4. Poor upper airway muscle responsiveness during sleep

The repeating cycle of collapse → desaturation → sympathetic nervous system surge → arousal elegantly explains the hypertension, atrial fibrillation and non-restorative sleep seen in the classic vignette.

Clinical Clues Examiners Expect You to Spot

Spot the underlying cause — these links earn marks in Part 1 and PACES alike:

• Acromegaly — macroglossia, big hands, headache, visual field loss

• AL amyloidosis — macroglossia + periorbital bruising + nephrotic-range proteinuria (a beloved MRCP combination)

• Hypothyroidism — screen with TFTs; treatment alone may shrink OSA

• Down syndrome, Marfan syndrome — hypotonic or collapsible airways

• Retrognathia — think previous orthognathic issues, class II malocclusion

Screening: Two Scores, Two Different Jobs

STOP-BANG (pre-test probability of OSA)

Scoring: 0–2 = low risk; 3–4 = intermediate; ≥5 = high risk (high risk correlates strongly with moderate-to-severe OSA).

Epworth Sleepiness Scale (severity of sleepiness)

Eight self-rated scenarios of dozing propensity, scored 0–3, total 0–24. ≥11 suggests excessive daytime sleepiness; ≥16 suggests severe sleepiness. It quantifies symptoms — it is not diagnostic of OSA and cannot replace a sleep study.

Choosing and Interpreting the Sleep Study

Trace interpretation pearls:

• Obstructive events: airflow falls but respiratory effort continues (chest and abdominal belts move).

• Central events: airflow and effort both absent.

• Cheyne–Stokes respiration: crescendo–decrescendo breathing with central apnoeas at the nadir — think heart failure.

• Treatment-emergent central sleep apnoea (complex apnoea): central events appear once CPAP is started — do not simply keep cranking the pressure.

The Comorbidity Map — Where Most Marks Hide

Examiner favourite: new or drug-resistant hypertension in an overweight snorer — the answer they are fishing for is a sleep study, not a fourth antihypertensive.

The Management Ladder (NICE-Aligned)

1. Lifestyle and reversible factors: ≥10% weight loss meaningfully reduces AHI; reduce evening alcohol and sedatives; positional measures (tennis-ball technique) for positional OSA; treat rhinitis and hypothyroidism.

2. CPAP — NICE TA139: recommended for adults with moderate or severe symptomatic OSAHS. Benefits: reduced sleepiness, better quality of life and driving-simulator performance, modest blood pressure reduction (~2 mmHg). Side effects: rhinitis, nasal dryness, mask pressure sores, aerophagia, air leak conjunctivitis, partner disturbance. Adherence is the rate-limiting step — early review and mask refitting matter.

3. Mandibular advancement devices (MADs) — NICE TA375: for mild OSAHS inadequately helped by lifestyle measures, or moderate–severe OSAHS when CPAP is not tolerated, contraindicated or declined. Requires adequate dentition; watch for TMJ pain and dental movement.

4. Bariatric surgery per standard NICE obesity criteria where BMI thresholds are met.

5. Surgical options: septoplasty/tonsillectomy in selected anatomical disease; multilevel pharyngeal surgery has limited evidence. Hypoglossal nerve stimulation is recognised in NICE interventional procedures guidance for carefully selected CPAP-intolerant patients (limited by BMI ceiling and absence of complete concentric collapse on drug-induced sleep endoscopy).

Driving: The DVLA Box You Cannot Afford to Miss

• A driver with OSA causing excessive sleepiness must not drive until symptoms are controlled — usually with established, effective treatment.

• Advise the patient of their legal responsibilities and document your advice verbatim in the notes.

• Group 2 entitlements (bus/lorry) are stricter: notification to DVLA and demonstrable compliance with effective treatment are required before re-licensing.

In PACES, raising driving unprompted earns easy safety marks. Omitting it in a sleepy lorry-driver scenario can fail the station outright.

Related Syndromes That Change Management

• Obesity-hypoventilation syndrome (OHS): BMI >30 plus daytime PaCO2 >6.0 kPa (45 mmHg) without another explanation. Clue on routine bloods: raised serum bicarbonate. Managed with NIV (often with CPAP for coexistent OSA) alongside weight management.

• Overlap syndrome (COPD + OSA): higher risk of hypercapnia, nocturnal desaturation and pulmonary hypertension; CPAP in this group improves outcomes versus no treatment.

• Central sleep apnoea / Cheyne–Stokes in heart failure: the treatment is optimisation of guideline-directed heart failure therapy. Crucially, adaptive servo-ventilation (ASV) is contraindicated in HFrEF (LVEF ≤45%) — the SERVE-HF trial showed increased cardiovascular mortality with ASV in this group.

2024–2025 Update: Tirzepatide (SURMOUNT-OSA)

This is the headline recent advance, and written examiners are already building stems around it:

• SURMOUNT-OSA (NEJM, 2024): 52-week randomised trials in adults with obesity and moderate-to-severe OSA, with and without concurrent CPAP.

• Tirzepatide (dual GIP/GLP-1 receptor agonist) reduced AHI by roughly 55–60% relative reduction — approximately 25–30 events/hour absolute — alongside 10–20% weight loss.

• In December 2024 the FDA approved tirzepatide for moderate-to-severe OSA with obesity — the first pharmacotherapy licensed for OSA, based on efficacy plus improvements in sleepiness, weight and patient-reported outcomes.

• Exam nuance: it is an adjunct for the patient with obesity-related OSA — not a replacement for CPAP in severe symptomatic disease; NICE appraisal status should be checked before UK prescribing; counsel on GI side effects and the need for gradual dose escalation.

Also on the radar: expanding home sleep apnoea testing pathways, and AI-assisted analysis of oximetry and flow traces — plausible futures for a data-interpretation station.

PACES Snapshot: The Sleepy Patient

A 10-minute skeleton you can rehearse:

1. Open: screen for the four cardinal features — snoring, witnessed apnoeas, unrefreshing sleep, daytime sleepiness (include Epworth-style quantification: dozing while driving? at traffic lights?).

2. Collateral: what does the partner notice at night?

3. Cause screen: weight trajectory, alcohol, sedatives, snoring, nasal obstruction; thyroid/acromegaly features.

4. Consequences: morning headaches, nocturia, mood, hypertension, arrhythmia, near-misses while driving.

5. Impact and ICE: occupation (driving!), shift work, safety-critical job, patient concerns and expectations.

6. Close with safety: advise on driving and DVLA responsibilities, agree investigations (limited sleep study), outline management pathway, and provide a senior-level summary.

Ten Rapid-Fire Pearls

1. AHI thresholds: 5 / 15 / 30 for mild / moderate / severe.

2. STOP-BANG ≥3 intermediate, ≥5 high risk.

3. Epworth ≥11 = excessive sleepiness; ≥16 = severe.

4. Resistant hypertension → think OSA and order a sleep study.

5. Macroglossia + periorbital bruising + proteinuria → AL amyloidosis with OSA.

6. CPAP for moderate–severe symptomatic OSAHS (TA139); MAD for mild or CPAP-intolerant (TA375).

7. Sleepy driver: stop driving + DVLA — safety before sympathy.

8. BMI >30 + daytime PaCO2 >6 kPa (bicarbonate raised on bloods) = OHS → NIV pathway.

9. Cheyne–Stokes + LVEF ≤45% → no ASV (SERVE-HF); optimise heart failure therapy.

10. Tirzepatide (2024): first drug licensed for moderate-to-severe OSA in adults with obesity — reduces AHI by over half in trial conditions.

Test Yourself (SBA Style)

Q1. A 48-year-old man, BMI 36 kg/m², neck 45 cm, Epworth 14, loud snoring with witnessed apnoeas and hypertension controlled on two agents. Best next investigation?

• A. Arterial blood gas

• B. In-laboratory polysomnography

• C. Limited home respiratory polygraphy

• D. Echocardiogram

• E. Overnight EEG

Answer: C. High pre-test probability, uncomplicated presentation — a limited home sleep study is first-line in most UK pathways. Reserve PSG (B) for suspected central apnoea or complex cases.

Q2. Limited sleep study confirms AHI 38/hour with daytime sleepiness; ABG shows normal PaCO2. Most appropriate management?

• A. Mandibular advancement device

• B. Positional therapy alone

• C. Watchful waiting with lifestyle advice

• D. CPAP

• E. Modafinil

Answer: D. Severe symptomatic OSAHS — CPAP is the NICE-recommended treatment. Modafinil has no routine role in untreated OSA.

Q3. A 70-year-old woman with ischaemic cardiomyopathy (LVEF 28%), Cheyne–Stokes respiration and a central apnoea index of 25/hour reports daytime sleepiness. Next step?

• A. Start adaptive servo-ventilation

• B. Increase CPAP pressure empirically

• C. Optimise guideline-directed heart failure therapy and review

• D. Immediate overnight NIV

• E. Trial of acetazolamide

Answer: C. Central sleep apnoea in HFrEF is treated by optimising heart failure management; ASV is contraindicated at LVEF ≤45% after SERVE-HF.

Takeaways

• Know the numbers cold: AHI 5/15/30, Epworth ≥11, STOP-BANG ≥3/≥5, PaCO2 6 kPa for OHS, neck >40/>43 cm.

• OSA is a systemic disease — hypertension, AF, diabetes, RTA risk — and the exam rewards the comorbidity links.

• Match the treatment to AHI and symptoms: CPAP (TA139) vs MAD (TA375), with surgery and nerve stimulation in selected cases.

• Driving is a safety-critical domain — mention it before the examiner does.

• And finally, be ready for the new era: tirzepatide in OSA with obesity is exactly the kind of recent-advance stem written exams have started using to separate the well-read from the well-crammed.