Autoimmune Fanconi Syndrome Presenting with Hypokalemic Paralysis in a Young Adult: A Renal-limited Sjögren Variant

Background: Hypokalemic paralysis is a reversible yet potentially life-threatening cause of acute flaccid weakness. While primary periodic paralysis is well recognised, secondary forms due to renal tubular dysfunction are often overlooked. Fanconi syndrome, a proximal tubulopathy, is an uncommon autoimmune manifestation of Sjögren’s syndrome, which more typically presents with distal renal tubular acidosis (RTA). Its occurrence in a 19-year-old young female is highly atypical and proximal tubular involvement in Sjögren’s is distinctly rare. Case Summary: We describe a 19-year-old female who presented with acute flaccid quadriparesis and severe hypokalaemia. Laboratory evaluation revealed hypophosphatemia, non-anion gap metabolic acidosis and inappropriately alkaline urine. Urinalysis showed phosphaturia, glucosuria and proteinuria, confirming Fanconi syndrome. Electromyography (EMG) demonstrated a myopathic pattern. Strongly positive Anti-Sjögren’s syndrome-related antigen A (Ro) antibody (anti-SSA/Ro) antibodies and polyclonal hypergammaglobulinemia suggested an autoimmune aetiology consistent with renal-limited Sjögren’s syndrome. Targeted correction of electrolytes, vitamin D deficiency and metabolic acidosis led to rapid and complete recovery. The combination of very young age and isolated proximal tubular dysfunction underscores the diagnostic challenge and highlights the importance of considering renal-limited autoimmune disease even without sicca symptoms. Conclusion: This case illustrates a rare presentation of autoimmune Fanconi syndrome manifesting as hypokalemic paralysis in a young female. Anti-SSA/Ro seropositivity and polyclonal hypergammaglobulinemia, despite absent sicca features, should prompt evaluation for renal-limited Sjögren’s syndrome. Early recognition is crucial, as timely metabolic correction results in complete clinical recovery.