A physiology-based approach to a patient with hyperkalemic renal tubular acidosis

ABSTRACT Hyperkalemic renal tubular acidosis is a non-anion gap metabolic acidosis that invariably indicates an abnormality in potassium, ammonium, and hydrogen ion secretion. In clinical practice, it is usually attributed to real or apparent hypoaldosteronism caused by diseases or drug toxicity. We describe a 54-year-old liver transplant patient that was admitted with flaccid muscle weakness associated with plasma potassium level of 9.25 mEq/L. Additional investigation revealed type 4 renal tubular acidosis and marked hypomagnesemia with high fractional excretion of magnesium. Relevant past medical history included a recent diagnosis of Paracoccidioidomycosis, a systemic fungal infection that is endemic in some parts of South America, and his outpatient medications contained trimethoprim-sulfamethoxazole, tacrolimus, and propranolol. In the present acid-base and electrolyte case study, we discuss a clinical approach for the diagnosis of hyperkalemic renal tubular acidosis and review the pathophysiology of this disorder.摘要：高钾性肾小管酸中毒（Hyperkalemic renal tubular acidosis）是一种正常阴离子间隙代谢性酸中毒（non-anion gap metabolic acidosis），始终提示钾、铵及氢离子分泌存在异常。临床实践中，该病通常由疾病或药物毒性引发的真性或假性醛固酮减少症（hypoaldosteronism）所致。本文报告一例54岁肝移植（liver transplant）患者，该患者因弛缓性肌无力（flaccid muscle weakness）入院，其血浆钾浓度达9.25毫当量/升（mEq/L）。进一步检查显示其患有4型肾小管酸中毒，伴显著低镁血症（hypomagnesemia）及镁排泄分数升高。患者相关既往病史包括近期确诊的副球孢子菌病（Paracoccidioidomycosis）——一种在南美部分地区流行的全身性真菌感染，其门诊用药包含甲氧苄啶-磺胺甲噁唑、他克莫司（tacrolimus）与普萘洛尔（propranolol）。在本次酸碱平衡与电解质紊乱病例研究中，我们探讨了高钾性肾小管酸中毒的临床诊断思路，并对该疾病的病理生理机制进行综述。