Differential Diagnosis

The patient presents with a complex clinical picture, including low calcium, rising creatinine, confusion, hallucinations, and a history of chronic kidney disease (CKD) and heart failure. The following differential diagnoses are considered:

• Single Most Likely Diagnosis
  • Chronic Kidney Disease (CKD) with Secondary Hyperparathyroidism: The patient's elevated parathyroid hormone (PTH) levels, despite low calcium, suggest secondary hyperparathyroidism, a common complication of CKD. The rising creatinine and history of CKD support this diagnosis.
• Other Likely Diagnoses
  • Hypocalcemia due to Vitamin D Deficiency: The patient's low calcium levels, despite elevated PTH, may be due to vitamin D deficiency, which is common in elderly patients and those with CKD.
  • Sepsis or Infection: The patient's confusion, hallucinations, and elevated white cell count may indicate an underlying infection or sepsis, which can be life-threatening in elderly patients with multiple comorbidities.
  • Medication-Induced QT Prolongation: The patient's ECG shows QT prolongation, which may be due to medication side effects, such as those caused by certain antibiotics or antipsychotics.
• Do Not Miss Diagnoses
  • Hyperphosphatemia-Induced Hypocalcemia: Although the patient's phosphate levels are not extremely high, hyperphosphatemia can cause hypocalcemia, and this diagnosis should not be missed, especially in patients with CKD.
  • Cardiac Arrhythmia or Myocardial Ischemia: The patient's history of heart failure and STEMI, combined with the current ECG findings, necessitate consideration of cardiac arrhythmia or myocardial ischemia as a potential cause of the patient's symptoms.
• Rare Diagnoses
  • Pseudohypoparathyroidism: This rare genetic disorder can cause resistance to PTH, leading to hypocalcemia and hyperphosphatemia, despite elevated PTH levels.
  • Osteomalacia or Rickets: Although less likely, osteomalacia or rickets should be considered in patients with CKD and hypocalcemia, especially if there is a history of vitamin D deficiency or phosphate wasting.