Differential Diagnosis

The patient's presentation with respiratory symptoms, nausea, vomiting, diarrhea, new-onset a-fib, elevated WBC, thrombocytopenia, pericardial effusion, and a cavitary lesion at the left lower lobe suggests a complex and potentially life-threatening condition. The following differential diagnoses are considered:

• Single most likely diagnosis
  • Lung Cancer with Metastasis and Paraneoplastic Syndrome: The patient's history of smoking, new-onset a-fib, and cavitary lesion at the left lower lobe are highly suggestive of lung cancer. The elevated WBC and thrombocytopenia could be indicative of metastasis or paraneoplastic syndrome. The pericardial effusion could be related to the cancer or a paraneoplastic syndrome.
• Other Likely diagnoses
  • Tuberculosis (TB): The cavitary lesion at the left lower lobe and the patient's symptoms could be consistent with TB, especially in the absence of regular medical care. The elevated WBC and thrombocytopenia could be indicative of a disseminated infection.
  • Sepsis: The patient's symptoms, elevated WBC, and thrombocytopenia could be indicative of sepsis, potentially due to a bacterial or fungal infection.
  • Lymphoma: The patient's symptoms, elevated WBC, and thrombocytopenia could be consistent with lymphoma, especially if there is involvement of the lung and pericardium.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Pulmonary Embolism (PE): Although the patient's symptoms are more suggestive of an infectious or malignant process, a PE could be present, especially with the new-onset a-fib and pericardial effusion.
  • Endocarditis: The patient's new-onset a-fib and pericardial effusion could be indicative of endocarditis, which would require prompt antibiotic treatment.
• Rare diagnoses
  • Wegener's Granulomatosis: The patient's symptoms, cavitary lesion, and pericardial effusion could be consistent with Wegener's granulomatosis, a rare autoimmune disorder.
  • Erdheim-Chester Disease: The patient's symptoms, cavitary lesion, and pericardial effusion could be consistent with Erdheim-Chester disease, a rare histiocytic disorder.