Table 3.

Teaching points

FS is characterized by proximal tubular dysfunction of the kidneys resulting in nonselective urinary wasting of electrolytes, uric acid, glucose, and amino acids, all of which are normally reabsorbed in the proximal tubule.

The clinical presentation of FS includes hypokalemia, hypophosphatemia, proximal renal tubular acidosis, hypouricemia, normoglycemic glycosuria, and aminoaciduria. It is classified as complete if all of the aforementioned features are present or partial if not.

FS can be inherited or acquired. One rare cause of acquired FS is MM as the monoclonal immunoglobulin light chains are toxic to the proximal tubular epithelial cells.

The development of severe electrolyte depletion, metabolic acidosis, hypouricemia, and/or normoglycemic glycosuria after HSCT in patients with MM should raise the clinical suspicion of FS—even in the presence of concurrent gastrointestinal symptoms, which are not uncommon after the procedure. The pathogenesis is unclear because these patients have already been partially treated and have lower free light chain levels than at diagnosis.

The mMajority of the patients who developed FS after HSCT had IgG kappa MM. These kappa light chains that cause proximal tubulopathy have been found to be highly resistant to proteolysis and capable of spontaneously forming intracellular crystals (vs. lambda).

Lenalidomide is a chemotherapeutic agent used in patients with MM that has been implicated to cause FS.

Acute acquired FS in patients with MM after HSCT appears to be a self-limited and transient phenomenon that requires timely and adequate electrolyte repletion and close monitoring.

FS, Fanconi syndrome; HSCT, hematopoietic stem cell transplantation; IgG, immunoglobulin G; MM, multiple myeloma.