Light chain proximal tubulopathy in a 59-year-old woman with Sjögren's syndrome: a case report and review of the literature.

Light chain proximal tubulopathy (LCPT) is a rare form of monoclonal gammopathy of renal significance (MGRS), characterized by the deposition of monoclonal light chains in proximal renal tubules. We present a case of a 59-year-old female with a 9-year established history of Sjögren’s syndrome (SS) who presented with progressive renal dysfunction. A comprehensive workup revealed a monoclonal IgA-kappa paraproteinemia and a renal biopsy confirmed LCPT. Her diagnosis of SS was re-confirmed with positive anti-SSA/Ro-52 antibodies and focal lymphocytic sialadenitis. The patient exhibited metabolic acidosis, hypophosphatemia, and hypokalemia, consistent with Fanconi syndrome. Notably, her autoimmune condition preceded the development of MGRS by nearly a decade. While this temporal association raises the possibility that chronic immune stimulation in SS could contribute to clonal plasma cell proliferation and subsequent LCPT, such a link remains speculative and cannot be established from a single case. This case highlights the importance of considering MGRS in SS patients with worsening renal tubular dysfunction.