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Difficulty: MediumFormulating a Differential Diagnosis

A 68-year-old man comes to the clinic due to a 6-week history of painful swelling in his wrists and ankles. The pain is severe, deep, aching, and exacerbated by weight-bearing. He also reports a 3-month history of a persistent dry cough and an unintentional 4-kg (8.8-lb) weight loss. He has a 40-pack-year smoking history but quit 5 years ago. His temperature is 37.2°C (99.0°F), blood pressure is 138/86 mmHg, heart rate is 88/min, and respiratory rate is 16/min. Physical examination reveals bulbous enlargement of the fingertips with increased convexity of the nail beds. There is palpable tenderness and warmth over the distal tibia, fibula, radius, and ulna bilaterally. Lung auscultation reveals decreased breath sounds and dullness to percussion in the right upper lobe. Complete blood count and basic metabolic panel are within normal limits. Plain radiographs of the lower extremities show symmetric, bilateral periosteal new bone formation along the distal diaphyses of the tibia and fibula. Which of the following is the most likely underlying diagnosis?

  1. Non-small cell lung cancerAnswer
  2. B
    Rheumatoid arthritis
  3. C
    Idiopathic pulmonary fibrosis
  4. D
    Granulomatosis with polyangiitis
  5. E
    Bronchiectasis

Answer

The correct diagnosis is non-small cell lung cancer.
The correct answer is non-small cell lung cancer. This patient's clinical presentation—digital clubbing, sudden-onset painful arthropathy, and radiographic evidence of periosteal new bone formation (periostitis)—constitutes the classic triad of hypertrophic pulmonary osteoarthropathy (HPOA). HPOA is a paraneoplastic syndrome that is strongly associated with intrathoracic malignancies, most notably non-small cell lung cancer (especially adenocarcinoma). The presence of a prominent smoking history, constitutional symptoms (weight loss), and focal right upper lobe physical exam findings (decreased breath sounds and dullness to percussion) further points toward a primary pulmonary malignancy as the underlying driver of his systemic symptoms.

Step-by-Step Solution

1
Synthesize the osteoarticular physical exam and radiographic findings.
The patient has digital clubbing (bulbous fingertips), arthritis/arthralgias (warmth/tenderness in wrists and ankles), and radiographic evidence of periostitis (periosteal new bone formation).
Recognizing this specific combination of symptoms as the triad of hypertrophic pulmonary osteoarthropathy (HPOA) narrows the differential diagnosis to thoracic pathologies.
2
Correlate the systemic paraneoplastic syndrome with the pulmonary findings and risk factors.
The patient has a 40-pack-year smoking history, weight loss, and focal right upper lobe findings (decreased breath sounds, dullness to percussion) suggestive of a pulmonary mass.
HPOA is most strongly associated with underlying intrathoracic malignancies, specifically primary lung cancer, which fits perfectly with the mass-like exam findings and smoking history.
3
Select the most appropriate primary diagnosis from the available options.
Non-small cell lung cancer (NSCLC), particularly adenocarcinoma, is the most common cause of HPOA.
Other options may explain isolated symptoms (like clubbing in bronchiectasis or joint pain in rheumatoid arthritis) but fail to explain the entire clinical and radiographic picture.

Key Concept

Hypertrophic pulmonary osteoarthropathy (HPOA) presents with digital clubbing, arthropathy, and periostitis, and is a paraneoplastic syndrome highly suggestive of an underlying non-small cell lung cancer.
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Formulating a Differential Diagnosis

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