Differential Diagnosis for Hypokalemia in an 18-month-old Boy
- Single most likely diagnosis
- Renal Tubular Acidosis (RTA) Type 1: This condition is characterized by a failure of the distal tubules to acidify the urine, leading to a metabolic acidosis with a high urine pH, hypokalemia, and often growth retardation. The patient's laboratory results showing a high urine pH (7.6) despite metabolic acidosis (low HCO3 and low pH on arterial blood gas) are consistent with this diagnosis.
- Other Likely diagnoses
- Bartter Syndrome: A rare genetic disorder affecting the kidneys, leading to excessive urinary loss of potassium, sodium, and chloride. It presents with hypokalemia, metabolic alkalosis, and often growth failure. However, the metabolic acidosis in this patient makes this less likely.
- Gitelman Syndrome: Similar to Bartter Syndrome but typically presents later in life and with hypomagnesemia, which is not mentioned in the case.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Adrenal Insufficiency: Although less likely given the specific electrolyte imbalances, adrenal insufficiency can cause hypotension, electrolyte disturbances, and failure to thrive. It's crucial to consider due to its potential severity and the need for urgent treatment.
- Pseudohypoaldosteronism Type 1: A condition characterized by resistance to aldosterone, leading to severe hyponatremia, hyperkalemia (less commonly hypokalemia in certain variants), and metabolic acidosis. The presentation can vary, making it a "do not miss" diagnosis due to its severity.
- Rare diagnoses
- Liddle Syndrome: A rare genetic disorder leading to excessive sodium absorption and potassium secretion in the collecting ducts, resulting in hypertension, hypokalemia, and metabolic alkalosis. The patient's low blood pressure makes this less likely.
- Other genetic disorders affecting renal electrolyte transport: There are several rare genetic conditions that can affect electrolyte balance and renal function, leading to hypokalemia among other symptoms. These would be considered if more common causes are ruled out.