Differential Diagnosis

The patient's presentation with normal blood pressure, hypokalemia, hypomagnesemia, and low urine calcium suggests a renal tubular disorder. Here's a categorized differential diagnosis:

• Single most likely diagnosis
  • A. Gitelman syndrome: This is the most likely diagnosis given the combination of hypokalemia, hypomagnesemia, and low urine calcium. Gitelman syndrome is a genetic disorder affecting the distal convoluted tubule, leading to impaired reabsorption of magnesium and potassium, and characteristically low urinary calcium excretion.
• Other Likely diagnoses
  • B. Bartter syndrome: While Bartter syndrome also presents with hypokalemia, it typically involves hypercalciuria (high urine calcium), which contrasts with the patient's low urine calcium. However, it's still a consideration due to the overlap in symptoms like hypokalemia and hypomagnesemia.
• Do Not Miss
  • None of the options provided (C. Liddle syndrome and D. Nephritic syndrome) fit well with the described symptoms. Liddle syndrome would present with hypertension, not normal blood pressure, and nephritic syndrome would typically involve significant proteinuria and hematuria, not specifically low urine calcium or the exact combination of electrolyte imbalances described.
• Rare diagnoses
  • Other rare genetic disorders affecting renal tubular function could potentially present with similar electrolyte imbalances, though they would be less likely than Gitelman syndrome given the specific combination of findings in this patient.

It's crucial to conduct further diagnostic testing, including genetic analysis and detailed electrolyte panels, to confirm the diagnosis and rule out other possibilities.