Differential Diagnosis

• Single most likely diagnosis
  • Hyperparathyroidism: The patient's high calcium level (14.2 mg/dl), low phosphorus level (2.4 mg/dl), and low parathyroid hormone level (7.0 pg/ml) are not consistent with primary hyperparathyroidism, which typically presents with high parathyroid hormone levels. However, the provided parathyroid hormone level is low, which might be seen in cases of parathyroid hormone-mediated hypercalcemia due to a parathyroid hormone-producing tumor or familial hypocalciuric hypercalcemia, but the low parathyroid hormone level here is more suggestive of a non-parathyroid hormone-mediated cause of hypercalcemia. Considering the clinical presentation, a more likely cause of the hypercalcemia could be related to malignancy, given the weight loss, chronic cough, and decreased breath sounds in the right middle lobe, suggesting a possible lung malignancy with hypercalcemia of malignancy. However, the most straightforward interpretation of the lab results provided (especially with the low parathyroid hormone level) points towards a non-parathyroid cause of hypercalcemia.
  • Malignancy-associated hypercalcemia: This diagnosis fits better with the low parathyroid hormone level, as malignancies can cause hypercalcemia through the production of parathyroid hormone-related protein (PTHrP) or other mechanisms, and the clinical presentation (weight loss, chronic cough, decreased breath sounds) suggests a possible malignancy.
• Other Likely diagnoses
  • Lung cancer: Given the chronic cough, weight loss, and decreased breath sounds in the right middle lobe, lung cancer is a strong consideration, especially as it can cause hypercalcemia of malignancy.
  • Other malignancies: Though less directly suggested by the symptoms, other cancers (e.g., breast, kidney) can also cause hypercalcemia of malignancy and should be considered, especially with the significant weight loss.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Pneumonia or lung abscess: Although the lung exam and symptoms could suggest malignancy, infectious causes like pneumonia or lung abscess must be considered due to their potential for serious consequences if not treated promptly.
  • Hypercalcemia of other causes: While less likely given the clinical context, other causes of hypercalcemia (e.g., vitamin D intoxication, sarcoidosis) should not be overlooked as they require different management.
• Rare diagnoses
  • Familial hypocalciuric hypercalcemia (FHH): Although the parathyroid hormone level is low, which is not typical for FHH, this condition can present with hypercalcemia and should be considered in the differential, especially if other tests (like urinary calcium excretion) are suggestive.
  • Multiple endocrine neoplasia (MEN) syndromes: These are rare genetic disorders that can lead to hyperparathyroidism among other endocrine abnormalities, but the low parathyroid hormone level makes this less likely unless there's a complex interplay of hormonal imbalances.