Case Study Series – The Art of Clinical Reasoning

#Case1: A Curious Case of Positional Dyspnea

Attending–Resident Dialogue Style

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Okay, 
In this article, we invite you to walk step-by-step through a real-world diagnostic challenge. At each stage, pause and ask yourself — what would I think next? What questions should I ask? What diagnoses come to mind?

Let’s dive in.

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🚪 Doorway Information

Let’s start with a case that feels just a little off from the beginning.

A 74-year-old woman comes in saying:
“I feel short of breath when I sit up.”

Vitals at triage:

• Temp: 36.7°C
• BP: 132/68 mmHg
• HR: 94
• RR: 20
• SpO₂: 91% sitting, 97% supine

🗣️ Have you seen anything like this before? A patient who desaturates simply by sitting up?

Let’s take this as a challenge. How would you approach it?

🔎 Imagine you’re the resident on call. Your attending is about to quiz you — are you ready?

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🧠 Step 1: Let’s Think Out Loud – Fact → Problem → Hypotheses

💬 So, what do we know so far?

Attending:
“Alright, quick case. A 74-year-old woman says she gets short of breath when she sits up. Supine, she feels fine. Her vitals are stable, but her O₂ saturation drops when she’s upright. First thoughts?”

Resident:
“…Hmm. That’s unusual. It sounds like… the opposite of orthopnea?”

🧠 Good observation. Positional dyspnea — but in the opposite direction.

Attending:
“Exactly. So — what’s the term for that?”

Resident:
“Honestly… I don’t think I’ve ever seen this before.”

Attending:
“Most people haven’t. But there’s a name for it: platypnea-orthodeoxia syndrome. Ever heard of it?”

Resident:
“I’ve maybe read the name somewhere, but definitely not in real life.”

Attending:
“Well, you’re about to see it in full color. Let’s build up your differential. If someone desaturates when sitting up, what could be happening physiologically?”

Resident:
“Well, her lungs are clear, and she feels better lying down. So… maybe there’s some kind of shunt that opens up when she’s upright?”

Attending:
“Great. So think through shunts. Where can they happen?”

Resident:
“Intra-cardiac, like a PFO. Or maybe in the lungs — like AV malformations?”

Attending:
“Exactly. Keep going.”

Resident:
“There’s also hepatopulmonary syndrome, right? I think that can cause shunting too?”

Attending:
“Nice recall. Now — before we jump ahead, let’s collect more history and exam. What do you want to know next?”

🧭 Are you thinking of the same differentials? Let’s move to data gathering.

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🔍 Step 2: What Do We Need to Know? (NTK)

Before jumping to tests, let’s outline the information we want.

💭 Take a moment: what questions would you ask this patient?

Resident:
“I’d ask about:

• Duration and progression of dyspnea
• Associated symptoms: fatigue, syncope, cough, leg swelling
• Liver disease, embolism history
• Social history: alcohol, smoking, travel”

Attending:
“Good. And physical exam?”

Resident:
“Clubbing, cyanosis, murmurs, signs of right or left heart failure, hepatomegaly.”

Attending:
“Let’s move on to what you find.”

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🫠 Step 3: History & Physical Exam

Let’s walk into the room with the resident.

Resident:
“She says it started about 3 months ago. It’s positional — worse sitting up, better when lying flat. No fever, no cough, no recent weight loss. No history of liver disease or cardiac issues.”

On exam:

• No cyanosis or clubbing
• No murmurs, no JVD or edema
• Lungs clear
• O₂ sat 91% upright → improves to 97% supine

Attending:
“Nice work. What are you thinking now?”

Resident:
“Definitely fits platypnea-orthodeoxia. I’d like to confirm with ABGs and echo with bubble study.”

✅ We’re honing in. Let’s see what the tests reveal.

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🔢 Step 4: What Did We Find?

• ABG:
• Supine: PaO₂ 85 mmHg
• Sitting: PaO₂ 60 mmHg
• TTE with bubble: positive → bubbles in LA within 3 beats
• TEE: large PFO with positional shunt
• Chest CT: no AVMs or ILD

Resident:
“So we have confirmed platypnea-orthodeoxia due to PFO.”

Attending:
“Yes. What makes it symptomatic now in her 70s?”

Resident:
“Maybe anatomical or hemodynamic changes with aging that unmask the shunt?”

Attending:
“Exactly.”

📌 Let’s lock in the diagnosis.

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✅ Final Diagnosis

Platypnea-Orthodeoxia Syndrome due to Patent Foramen Ovale (PFO)

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💬 Clinical Reflection

Let’s pause here.

💭 What made this case different from other causes of dyspnea?

Attending:
“So what’s the big clue that told you this wasn’t just COPD or CHF?”

Resident:
“The positional nature — she improved lying flat, and her lungs and heart exam were normal.”

Attending:
“Right. When you see hypoxia without clear pulmonary findings, and it’s posture-sensitive, think shunt.”

🧠 A rare but revealing clue. Now let’s shift to a broader perspective.

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🧠 Discussion: Let’s Try Another Lens

📖 Let’s revisit what we’ve learned so far:

A 74-year-old woman presents with posture-dependent dyspnea — specifically worse when sitting up — with a corresponding drop in oxygen saturation.

We walked through this together step-by-step:

• Recognized the unusual positional pattern
• Explored differential diagnoses involving shunt physiology
• Confirmed the diagnosis of Platypnea-Orthodeoxia Syndrome due to PFO with a targeted workup

🗣️ Now, let’s flip the script.

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💭 When “Heart Failure” Isn’t the Heart

Before we jump into our next case — let’s take a moment to reflect:

A patient presents with dyspnea, fatigue, lower extremity edema… sounds like heart failure, right?

But what if the lung exam is clear?
What if the BNP is mildly elevated, but not diagnostic?
What if the echo shows a dilated right ventricle, but a normal left side?

🧭 In moments like these, it’s worth asking:
Could this be pulmonary hypertension? And what kind?

Let’s meet our second patient.

Attending:
“What if the patient were a 65-year-old obese man, with exertional dyspnea, snoring, and daytime sleepiness, plus mild LE edema?”

Resident:
“Sounds like possible sleep apnea or obesity hypoventilation?”

Attending:
“Let’s explore. Here’s his data:

• BMI 42, neck circumference 46 cm
• PaCO₂ 54, PaO₂ 64
• Echo: RV hypertrophy, PASP 60 mmHg”

Resident:
“Obesity Hypoventilation Syndrome with pulmonary hypertension. Probably Group 3 PH.”

Attending:
“Exactly. Now let’s recall the PH classification.”

🪞 Let’s pause and reflect.

This case looked like classic heart failure — dyspnea, edema, and fatigue. But on closer inspection, it wasn’t the left heart at fault. It was the lungs and right heart.

🗣️ So next time you see “heart failure–like” symptoms, ask yourself:

• Is the left heart truly failing?
• Could this be Group 3 PH from obesity or chronic hypoxia?
• Are we missing pulmonary causes beneath the surface?

These clues can keep you from mislabeling the diagnosis — and lead you to the right treatment.

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🫀 Understanding Pulmonary Hypertension

When we suspect pulmonary hypertension (PH), classification can help us—but even more important is to recognize the shared physiology:

• Increased pulmonary vascular resistance
• Progressive right heart strain
• Often subtle symptoms initially mimicking CHF

Let’s briefly revisit the types.

📂 Pulmonary Hypertension Groups

Group	Cause	Examples
1	Pulmonary Arterial HTN	IPAH, connective tissue disease
2	Left Heart Disease	HFpEF, mitral regurgitation
3	Lung/Hypoxia	COPD, ILD, OHS
4	Chronic Thromboembolic Disease	CTEPH
5	Miscellaneous	Sarcoid, sickle cell, CKD

*Note: In Japan, edoxaban has recently been approved for use in chronic thromboembolic pulmonary hypertension (CTEPH), expanding anticoagulation options beyond traditional warfarin for long-term outpatient management.*

📝 Key Takeaway

• Platypnea = upright dyspnea; orthodeoxia = upright hypoxia
• Think shunt: PFO, AVM, HPS
• Positional changes in O₂ sat are diagnostic clues
• Obesity + hypercapnia + RV findings = suspect Group 3 PH

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💡 Clinical Pearls

• “If oxygen drops when sitting up, think shunt.”
• Platypnea-orthodeoxia is rare but diagnostic when recognized.
• PFOs can remain silent for decades before symptoms emerge.

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📌 Take Home Message

• Platypnea-orthodeoxia syndrome should be suspected in posture-dependent dyspnea with normal lung findings.
• Obesity hypoventilation can masquerade as CHF — think beyond the left heart.

🧭 Keep your differential wide when dyspnea doesn’t behave the way you expect.

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🧭 Looking Ahead

If this case sparked your interest, here are more articles to explore:

• 👉 Symptom-Based Approach Index : 🩺 Symptom-Based Clinical Reasoning
• 👉 Mock Patient Scripts: Top Page
• 👉 日本語版はこちら

Each case brings a different clinical twist — from subtle signs to complex pathophysiology. Dive in!

If this case sparked your interest, we invite you to explore more in this series:

• What if hypoxia persists after pneumonia resolves?
• Can POCUS help you differentiate causes of dyspnea?
• When should you suspect pulmonary AVMs?

Stay tuned for future cases.

📚 References & Recommended Reading

• Agrawal A. Platypnea-Orthodeoxia Syndrome. Circulation. 2007;116\:e319–e321.
• Shujaat A et al. Platypnea-orthodeoxia syndrome: an overview. Postgrad Med J. 2012;88(1044):520–524.
• Simonneau G, et al. Haemodynamic definitions and updated clinical classification of pulmonary hypertension. Eur Respir J. 2019.
• Japanese Ministry of Health Notice on Edoxaban Approval for CTEPH, 2023.

Recommended Book: ダ・ヴィンチのカルテ（中山祐次郎 著）— A thought-provoking read on clinical decision-making and diagnostic process in real patients.