Light chain proximal tubulopathy

CASE PRESENTATIONA 55-year-old Caucasian woman presented to her primary care physician with complaints of progressive fatigue for several months, dyspnea with minimal exertion, loss of appetite, 15-pound weight loss, and recurrent low-grade fevers. Past medical history was significant only for migraine headaches. The patient was taking no prescription or over-the-counter medications. There was no history of environmental toxin exposure, recent travel, smoking, excess alcohol consumption, or use of illicit drugs. She was empirically treated with a course of esomeprazole and amoxicillin.The patient returned 2 weeks later and reported no improvement in her symptoms. Laboratory studies revealed anemia, thrombocytopenia, hypercalcemia, and acute renal failure. The patient was admitted for further evaluation.Upon admission, physical examination revealed a well nourished but pale female in no acute distress. Her blood pressure was 156/70 mm Hg, pulse 96 bpm, temperature 98.6 F, respiratory rate 20 breaths/min, and pulse oximetry 100% on room air. Cardiac and pulmonary examinations were unremarkable. Abdominal examination revealed splenomegaly with a palpable liver edge 1–2 cm below the right costal margin. Laboratory testing (Table 1) was notable for a hemoglobin of 6.1 g/dl (normal range, 11.0–15.0 g/dl), platelet count 112 K/mm3 (nl 150–400 K/mm3), creatinine 3.7 mg/dl, BUN 34 mg/dl, and calcium 12.4 mg/dl (nl 8.5–10.1 mg/dl). Liver function tests, coagulation studies, and parathyroid hormone levels were normal. Urinalysis revealed 1+ protein, 1+ glucose, and trace blood. Negative serologies included anti-glomerular basement membrane antibody, proteinase-3 anti-neutrophil cytoplasmic antibodies, and myeloperoxidase anti-neutrophil cytoplasmic antibodies. Serum complement levels were mildly elevated with C3 179.0 mg/dl (nl 75–135 mg/dl) and C4 41.9 mg/dl (nl 9–36 mg/dl). Serum protein electrophoresis with immunofixation showed no monoclonal protein. A bone marrow biopsy revealed normocellular marrow with no evidence of lymphoma or a plasma cell dyscrasia. A non-contrast computed tomography scan of the chest, abdomen, and pelvis was notable for splenomegaly (18 × 15 × 10 cm) with a hypodense area measuring 7 × 7 × 4 cm and mild hepatomegaly. The kidneys measured 11.7 and 12 cm in length by ultrasound, without evidence of obstruction. A skeletal survey showed no abnormalities.The patient was treated with hydration and a single dose of pamidronate. At the time of discharge 6 days later, her creatinine had fallen to 1.9 mg/dl, and her calcium had normalized.The patient was seen in nephrologic consultation 1 week after discharge, at which time her creatinine had declined to 1.5 mg/dl. Computed tomography scan was repeated with contrast and revealed a 19 × 16 × 10 cm spleen with an ill-defined 11 × 11 × 13 cm mass with areas of probable necrosis. In light of the absence of a clear indication for splenectomy, a renal biopsy was performed to determine the cause of the patient's persistent renal dysfunction.