Case Presentation: A 12 month old female with a prior episode of hyperkalemia in the setting of diarrheal illness presented to the Emergency Department with four days of non-bloody, non-bilious vomiting and three days of non-bloody loose stools. Initial outpatient evaluation included normal abdominal ultrasound and serum potassium of 7.1 mEq/L. Patient was admitted for treatment of hyperkalemia with a repeat serum potassium of 7.3 mEq/L. She was afebrile with vitals appropriate for age. Physical exam was significant for bilateral patellar hyperreflexia, non-focal decreased global tone, and unremarkable cardiorespiratory and abdominal exams. Additional labs were notable for non-anion gap metabolic acidosis with bicarbonate of 18.1 mEq/L without acidemia (capillary pH 7.39), hyperchloremia of 118 mmol/ L, normal aldosterone of 4 ng/dL (reference 2-37 ng/dL) , and decreased renin of 0.12 ng/mL (reference 0.25-5.82 ng/mL). Morning cortisol was normal without hyponatremia. EKG was without sequela of hyperkalemia. She was treated with furosemide, Kayexalate, and IV fluids. Her hyperkalemia initally improved with these interventions and a low potassium diet; however, she continued to require daily Kayexalate for persistent hyperkalemia despite resolution of loose stools. Further work up was remarkable for a low urine transtubular potassium gradient at 2.3. She ultimately required hydrochlorothiazide and a low potassium diet to maintain normal potassium and was discharged with suspected pseudohypoaldosteronism type II (PHAII). On subsequent follow up, she continues to require hydrochlorothiazide to maintain normal potassium levels with return of hyperkalemia during all attempted weaning trials.
Discussion: The initial evaluation of this patient’s hyperkalemia required assessment of cardiac effects and hospitalization for treatment to prevent further deterioration. The recurrent presentation and persistent hyperkalemia despite appropriate interventions prompted further investigation. The constellation of metabolic acidosis, decreased transtubular potassium gradient, suppressed plasma renin levels, and relatively suppressed aldosterone in the context of hyperkalemia as well as normal glomerular filtration and a robust response to thiazide diuretics was highly suggestive of pseudohypoaldosteronism type II. Low plasma renin sets this etiology apart from other causes of hyperkalemia such as chronic kidney disease, hypoaldosteronism, type 4 renal tubular acidosis, and primary adrenal insufficiency. Pathogenesis is thought to be caused by inactivating mutations leading to increased Na-Cl co-transporter activity and inhibition of aldosterone sensitive receptors in the distal renal tubules. Although testing with a Pediatric Disease Panel has been negative for known genetic variants of pseudohypoaldosteronism in this patient, research is ongoing to further identify genetic causes of PHAII. The treatment for pseudohypoaldosteronism focuses on correcting electrolyte abnormalities, often with the use of thiazide diuretics, and the treatment of hypertension should it arise.
Conclusions: This case illustrates a rare cause of persistent hyperkalemia consistent with pseudohypoaldosteronism type II. Awareness of the combination of hyperkalemia, normal glomerular filtration, low plasma renin, and a non-gap metabolic acidosis can lead to prompt diagnosis and treatment with thiazide diuretics.