Sleep Study is the Most Appropriate Investigation
A sleep study (polysomnography) is the most appropriate investigation to establish the diagnosis in this patient presenting with classic features of obstructive sleep apnea (OSA) with associated right heart failure (cor pulmonale). 1, 2
Clinical Reasoning
This patient presents with a constellation of symptoms highly suggestive of OSA:
- Daytime somnolence and poor concentration - cardinal symptoms of OSA 2, 3
- Nocturia - occurs due to increased atrial natriuretic peptide release from right atrial stretch in OSA 1
- Progressive shortness of breath - suggests developing right heart failure secondary to chronic OSA 1
- Obesity - major risk factor for OSA (BMI >30 kg/m²) 2, 4
- Bilateral lower limb edema - indicates right ventricular dysfunction from chronic pulmonary hypertension due to untreated OSA 1, 5
- Normal lung auscultation - rules out primary pulmonary pathology 1
Why Sleep Study First
The American Academy of Sleep Medicine recommends objective testing with polysomnography to confirm OSA diagnosis and determine severity. 2 This is the gold standard diagnostic test that will:
- Quantify the apnea-hypopnea index (AHI) to establish disease severity 1, 6
- Document oxygen desaturations during sleep 3, 6
- Guide treatment decisions regarding CPAP therapy 6
- Assess for other sleep disorders that may coexist 7, 6
The European Urology Association guidelines specifically identify OSA as a key condition in the "SCREeN" framework (Sleep medicine, Cardiovascular, Renal, Endocrine, Neurology) when evaluating patients with nocturia and peripheral edema. 1 The screening question "Have you been told that you gasp or stop breathing at night?" should be asked, along with "Do you wake up without feeling refreshed? Do you fall asleep in the day?" 1
Why Not the Other Options
Chest X-ray would be reasonable as a secondary investigation to assess for cardiomegaly or pulmonary hypertension, but it does not establish the underlying diagnosis of OSA. 1
Echocardiography may eventually be needed to assess right ventricular function and pulmonary pressures, but the primary diagnosis must be established first. 1, 5 The cardiac dysfunction is secondary to OSA, not the primary problem.
High-resolution CT lung is unnecessary given normal breath sounds and would not diagnose OSA. 1
Clinical Pitfalls to Avoid
- Do not assume this is primary heart failure - the normal lung examination and obesity point toward OSA as the primary etiology with secondary cardiac effects 1, 2
- Do not delay sleep study - untreated OSA with cor pulmonale has significant mortality implications 6
- Recognize the high pretest probability - this patient has multiple high-risk features (obesity, daytime sleepiness, nocturia, edema) making the pretest probability of moderate-to-severe OSA very high 4, 8
The STOP-BANG questionnaire has 98% effectiveness in predicting OSA diagnosis and includes symptoms, age, BMI, neck circumference, and hypertension - many of which this patient likely has. 4