What is the most likely cause of the pleural effusion in a 53-year-old female with a history of hypertension, obesity, depression, and breast cancer, presenting with worsening cough, fatigue, poor appetite, and chest discomfort, with laboratory results indicating elevated lactate dehydrogenase (LDH) and protein levels in the pleural fluid?

Differential Diagnosis for Pleural Effusion

• Single most likely diagnosis
  • Malignant effusion: The patient has a history of breast cancer treated with chemotherapy and mastectomy four years ago. The presence of a large right pleural effusion, decreased breath sounds on the right base, and the fluid analysis showing a high LDH (284) and low glucose (7) are suggestive of a malignant effusion. The lymphocyte predominance (65%) in the fluid also supports this diagnosis.
• Other Likely diagnoses
  • Pneumonic effusion: Although the patient does not have fever or chills, the exposure to a family member with an upper respiratory illness and the worsening cough could suggest a pneumonia. The fluid analysis shows a high white cell count (5600) and a low pH (7.15), which could be seen in a parapneumonic effusion.
  • Heart failure: The patient has a history of hypertension and obesity, which are risk factors for heart failure. However, the lack of lower extremity edema and the fluid analysis do not strongly support this diagnosis.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Empyema: Although the patient does not have fever or chills, the low pH (7.15) and high LDH (284) in the fluid could suggest an empyema. This diagnosis would require prompt antibiotic treatment and possible drainage.
  • Pulmonary embolism: The patient has a history of breast cancer and recent chemotherapy, which increases the risk of pulmonary embolism. The chest discomfort on the right side with deep breaths could be suggestive of a pulmonary embolism.
• Rare diagnoses
  • Chylothorax: The fluid analysis shows a high triglyceride level (not explicitly stated, but cholesterol is 106), which could suggest a chylothorax. However, this diagnosis is less likely given the patient's presentation and history.
  • Tuberculous pleurisy: The patient's symptoms and fluid analysis do not strongly support this diagnosis, but it could be considered in the differential diagnosis, especially if the patient has a history of exposure to tuberculosis or if the lymphocyte count is very high.