Polyuria and Hypokalemia in an Adolescent: Deciphering the Dual Tubulopathy of Primary Sjögren’s Syndrome
This case highlights the rare occurrence of dual tubular defects in a young patient with primary Sjögren’s syndrome, emphasizing the need for careful diagnostic evaluation in similar presentations.
Where it sits
this study against the rest of the desmopressin corpusSummary and findings
This case report describes a 17-year-old female with a 5-year history of polydipsia and polyuria, daily intake/output of 6–7 L, and severe hypokalemia. Desmopressin was administered, resulting in a urine osmolality that remained below 150 mOsm/kg, confirming nephrogenic diabetes insipidus. The patient was diagnosed with primary Sjögren’s syndrome presenting with dual tubular manifestations.
Abstract
Abstract Background Primary Sjögren’s syndrome (pSS) is a systemic autoimmune disorder usually occurred in old-aged women. It can involve the kidneys, most commonly causing distal renal tubular acidosis (dRTA). Overt nephrogenic diabetes insipidus (NDI) is rare, and the simultaneous occurrence of both tubular defects as the presenting feature of pSS, particularly in adolescents, is exceptional and presents a challenging diagnostic puzzle. Case presentation: We present a case of a 17-year-old female presented with a 5-year history of polydipsia and polyuria (daily intake/output 6–7 L), who was found to have severe hypokalemia, hyperchloremic normal anion-gap metabolic acidosis and inappropriately alkaline urine, confirming distal RTA. Water deprivation test with desmopressin demonstrated a urine osmolality that remained below 150 mOsm/kg despite rising serum osmolality and lacked significant increase after desmopressin, establishing the diagnosis of NDI. Positive anti-SSA/SSB, objective sicca findings, and renal biopsy revealing active tubulointerstitial nephritis led to the diagnosis of pSS with dual tubular manifestations. Treatment with prednisone, mycophenolate mofetil, hydrochlorothiazide, and high-dose potassium supplements led to significant clinical and biochemical improvement. Conclusions This case illustrates a systematic approach to polyuria and hypokalemia in an adolescent, unraveling a rare dual tubulopathy as the initial manifestation of pSS. We propose that NDI in this setting may result from a “two-hit” mechanism: direct autoimmune injury to the collecting duct and profound hypokalemia-induced downregulation of aquaporin-2. Recognizing this association and initiating early immunosuppression can partially reverse tubular dysfunction and improve long-term outcomes.