Differential Diagnosis for Raised Calcium with Low Normal Phosphate, Low PTH, Normal Vitamin D, Abdominal Lymphadenopathy, and Stable CKD

• Single Most Likely Diagnosis
  • Lymphoma: This is a strong consideration given the abdominal lymphadenopathy. Lymphoma can cause hypercalcemia through various mechanisms, including the production of parathyroid hormone-related protein (PTHrP) or other cytokines that stimulate osteoclast activity, leading to increased bone resorption. The low PTH level in the context of hypercalcemia supports a PTHrP-mediated process or another non-PTH mediated mechanism of hypercalcemia.
• Other Likely Diagnoses
  • Multiple Myeloma: Although less directly linked to abdominal lymphadenopathy, multiple myeloma is another malignancy that can cause hypercalcemia, typically through the production of osteoclast-activating factors. The absence of elevated PTH and normal vitamin D levels, along with low normal phosphate, fits with this diagnosis.
  • Vitamin A Intoxication: While vitamin D levels are normal, excessive intake of vitamin A can lead to hypercalcemia. However, this would typically be associated with a history of excessive vitamin A supplementation.
  • Familial Hypocalciuric Hypercalcemia (FHH): Although PTH is low, FHH could be considered, especially if there's a family history. However, the presence of abdominal lymphadenopathy makes this less likely.
• Do Not Miss Diagnoses
  • Hypercalcemia of Malignancy due to PTHrP or Other Factors: It's crucial not to miss other malignancies that could cause hypercalcemia through PTHrP or other mechanisms. The presence of abdominal lymphadenopathy already points towards a possible malignancy, but other primary sites should be considered.
  • Sarcoidosis: Although less common, sarcoidosis can cause hypercalcemia due to increased conversion of vitamin D to its active form, leading to increased intestinal absorption of calcium. However, vitamin D levels are reported as normal, which makes this less likely unless the disease process is altering the active form of vitamin D not accounted for in standard measurements.
• Rare Diagnoses
  • Thyroid Disorders: Rarely, hyperthyroidism can cause hypercalcemia due to increased bone turnover. However, this would typically be associated with other symptoms of hyperthyroidism.
  • Adrenal Insufficiency: Very rarely, adrenal insufficiency can lead to hypercalcemia, but this would typically be associated with other clinical findings such as hypotension and electrolyte imbalances.
  • Immobilization Hypercalcemia: In patients with high bone turnover states (e.g., Paget's disease, extensive bone metastases), immobilization can lead to hypercalcemia. However, this diagnosis would require a specific context of recent immobilization and underlying bone disease.