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Difficulty: HardRheumatology and Immunology

A 62-year-old woman comes to the emergency department complaining of progressively worsening shortness of breath and right-sided pleuritic chest pain over the past two weeks. She has a 12-year history of seropositive rheumatoid arthritis with severe joint deformities. Her current medications include methotrexate, etanercept, and folic acid. Her temperature is 37.2°C (99.0°F), blood pressure is 132/84 mmHg, pulse is 88/min, and respirations are 22/min. Oxygen saturation is 94% on room air. Physical examination reveals decreased breath sounds and dullness to percussion over the right lower lung field. Jugular venous pressure is 6 cm H2O. Cardiac auscultation shows a regular rate and rhythm with no murmurs or gallops. Examination of the hands shows ulnar deviation of the fingers and subluxation of the metacarpophalangeal joints. A chest radiograph demonstrates a moderate-sized right pleural effusion. A diagnostic thoracentesis is performed. Which of the following pleural fluid profiles is most characteristic of the pulmonary manifestation of this patient's underlying autoimmune disease?

  1. Glucose concentration of 15 mg/dL and lactate dehydrogenase (LDH) of 850 U/LAnswer
  2. B
    Glucose concentration of 95 mg/dL and lactate dehydrogenase (LDH) of 110 U/L
  3. C
    Pleural fluid pH of 7.45 and total protein of 2.1 g/dL
  4. D
    Predominantly polymorphonuclear leukocytes with a positive Gram stain
  5. E
    Elevated triglyceride concentration greater than 110 mg/dL

Answer

An exudative pleural fluid profile with a very low glucose concentration and high lactate dehydrogenase (LDH) is characteristic of rheumatoid pleuritis.
This patient with a long-standing history of severe rheumatoid arthritis (RA) is presenting with a right-sided pleural effusion. Pleural involvement (rheumatoid pleuritis) is a well-recognized extra-articular manifestation of RA, most commonly occurring in men and in patients with subcutaneous nodules and high rheumatoid factor titers. RA pleural effusions are characteristically exudative. What makes them unique is their specific biochemical profile: they typically exhibit a markedly low glucose concentration (often less than 30 mg/dL), an extremely high lactate dehydrogenase (LDH) level (often greater than 700 U/L), and a low pH (often less than 7.20). The low glucose is attributed to a localized block in glucose transport across the inflamed pleura combined with increased consumption by the prominent inflammatory cells in the fluid. Therefore, an exudative profile with a glucose of 15 mg/dL and highly elevated LDH strongly and specifically points to rheumatoid pleuritis.

Step-by-Step Solution

1
Analyze the clinical presentation and physical examination findings.
The patient has long-standing, severe rheumatoid arthritis (RA) and now presents with a unilateral pleural effusion without clinical signs of right heart failure (normal JVP) or systemic bacterial infection (afebrile).
Establishing the pre-test probability of an extra-articular manifestation of rheumatoid arthritis versus a secondary complication like heart failure or pneumonia.
2
Identify the specific biochemical characteristics of rheumatoid pleural effusions.
Rheumatoid pleuritis classically produces an exudative effusion characterized by a very low glucose level (< 30 mg/dL), a high LDH level (> 700 U/L), and a low pH (< 7.20).
This specific profile is caused by defective glucose transport across the inflamed pleura and high metabolic consumption by inflammatory cells, which helps differentiate RA effusions from other exudates.
3
Evaluate the given answer choices against known pleural fluid profiles.
The profile featuring a glucose of 15 mg/dL and LDH of 850 U/L perfectly matches the classic findings of an RA pleural effusion.
The other options represent transudates, bacterial empyema, or chylothorax, which are inconsistent with the patient's presentation of a sterile autoimmune effusion.

Key Concept

Rheumatoid pleuritis typically presents as an exudative pleural effusion characterized by profoundly low glucose levels (< 30 mg/dL), high lactate dehydrogenase (LDH) levels, and low pH.
Estimated Time:1m 15s
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Topics

Rheumatology and Immunology

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