RESUMEN
Fanconi syndrome (FS) is a complex disorder characterized by a reabsorption defect in the proximal renal tubule (PT), leading to urinary loss of molecules such as glucose, phosphate, calcium, amino acids, bicarbonate, potassium, and low-molecular-weight proteins. Its etiology can be genetic or acquired, with drug toxicity being a significant cause of the acquired forms. The heterogeneous manifestations of FS, whether in its partial or complete form, can pose challenges in the emergency department; nevertheless, it should be considered in certain patients, as understanding its cause is crucial for initiating effective treatment. We present the case of a 59-year-old female patient with FS who was treated with lenalidomide in the context of stage III IgG kappa multiple myeloma according to the Salmon Durie classification. We highlight the recurrent nature of this syndrome in this patient.