Light chain proximal tubulopathy

Abstract

CASE PRESENTATION A 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 156/70mmHg, pulse 96bpm, temperature 98.6F, respiratory rate 20breaths/min, and pulse oximetry 100% on room air. Cardiac and pulmonary examinations were unremarkable. Abdominal examination revealed splenomegaly with a palpable liver edge 1–2cm below the right costal margin. Laboratory testing (Table 1) was notable for a hemoglobin of 6.1g/dl (normal range, 11.0–15.0g/dl), platelet count 112K/mm 3 (nl 150–400K/mm 3 ), creatinine 3.7mg/dl, BUN 34mg/dl, and calcium 12.4mg/dl (nl 8.5–10.1mg/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 179.0mg/dl (nl 75–135mg/dl) and C4 41.9mg/dl (nl 9–36mg/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 × 10cm) with a hypodense area measuring 7 × 7 × 4cm and mild hepatomegaly. The kidneys measured 11.7 and 12cm 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 1.9mg/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 1.5mg/dl. Computed tomography scan was repeated with contrast and revealed a 19 × 16 × 10cm spleen with an ill-defined 11 × 11 × 13cm 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.