Chronic cough

A 59-year-old woman was admitted to our hospital with chronic cough. Her medical history included glaucoma without medication and a resected benign ovarian cyst. In addition, she had been diagnosed with elevated immunoglobulin G (IgG) levels 3 years prior to admission. Three months before her admission, she noticed a sore throat and cough without sputum. She had been diagnosed with pneumonia because of pulmonary infiltration on chest radiography, and levofloxacin was prescribed in another clinic. However, her symptoms did not resolve, and she was referred to our hospital.

On admission, chest auscultation revealed attenuated respiratory sounds in the left upper lung. Complete blood counts revealed leukocytosis with predominant neutrophils (12,300/μL (normal, <9,000); neutrophil, 93%). Blood biochemistry revealed hypoalbuminemia (3.3 g/dL), elevated C-reactive protein (10.4 mg/dL), high-soluble interleukin-2 receptor (3,940 IU/dL (normal, <550 IU/dL)), and normal IgG (1,392 mg/dL (normal, <1,700 mg/dL)). However, immunofixation of the serum revealed a low amount of monoclonal IgG kappa. Others including serum electrolytes, blood urea (9.2 mg/dL), creatinine (0.60 mg/dL), IgA (271 mg/dL), IgM (103 mg/dL), C3 (106 mg/dL), and C4 (34 mg/dL) were within normal limits. Serum tests for PR3-ANCA, MPO-ANCA, anti-Ri antibody, anti-Hu antibody, anti-Yo antibody, anti-dsDNA IgG antibody, and anti-dsDNA IgM were all negative. Despite repetitive evaluations, the patient tested negative for cryoglobulin. Antibody tests for hepatitis B virus, hepatitis C virus, and human immunodeficiency virus (HIV) were also negative. Computed tomography (CT) showed a tumor combined with infiltration in the left lower lobe.

Bone marrow specimens revealed a normal population without the proliferation of plasma cells. Despite normal eGFR, her urine was positive for protein, and the estimated daily urine protein amount was 1.36 g/g. Urinary protein was mainly albumin, and urinary monoclonal gamma globulin was absent. Renal biopsy revealed mesangial proliferation and a thickened glomerular basal membrane. PAS-positive and Congo red-negative deposits were observed in the glomerular capillary walls. Immunofluorescence staining was positive for IgG and C3 in the deposits. Immunohistochemistry showed positivity for kappa light chain and IgG3 and negative for lambda light chain IgG1, IgG2, IgG4, and C1q (data not shown). Electron microscopy indicated randomly aligned tubular structures located in the subendothelial and mesangial areas of the glomeruli. The diameter of these tubular structures was approximately 50 nm.