What is the most likely diagnosis for a 58-year-old woman with progressive abdominal pain, constipation, nausea, chronic cough, significant weight loss, fatigue, hypercalcemia, and impaired renal function, who has a history of tobacco use for 30 years and presents with tachycardia, hypotension, and decreased breath sounds in the right middle lobe?

Differential Diagnosis

• Single most likely diagnosis
  • C. Squamous cell lung cancer: The patient's long history of tobacco use, chronic cough, weight loss, and fatigue are all consistent with lung cancer. The decreased breath sounds in the right middle lobe could indicate a mass or obstruction, which is further supported by the patient's symptoms and history.
• Other Likely diagnoses
  • A. Primary hyperparathyroidism: The patient's elevated calcium level (14.2) and low phosphorus level (2.4) could suggest primary hyperparathyroidism. However, this diagnosis alone does not account for all of the patient's symptoms, such as the chronic cough and weight loss.
  • B. Multiple myeloma: Although multiple myeloma can cause hypercalcemia, the patient's presentation and laboratory results are not as strongly suggestive of this diagnosis as they are of lung cancer.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Pneumonia or lung abscess: The patient's decreased breath sounds and chronic cough could indicate a pulmonary infection, which would require prompt treatment.
  • Malignant bowel obstruction: The patient's abdominal pain, constipation, and nausea could be indicative of a bowel obstruction, which is a medical emergency.
• Rare diagnoses
  • Paraneoplastic syndrome: The patient's hypercalcemia and other symptoms could be due to a paraneoplastic syndrome associated with a malignancy other than lung cancer.
  • Sarcoidosis: Although less likely, sarcoidosis could cause hypercalcemia, lung symptoms, and other systemic symptoms, and should be considered in the differential diagnosis.