Cases from the Brigham and Women's Hospital

An 82 year old female with a recent history of being diagnosed with pneumonia presents to the emergency department with generalized weakness and fatigue.  She syas that her urine has been lately dark-colored in the morning. She is found to have hematuria and proteinuria.  Her past medical history is notable for recent pneumonia, asthma, chronic bronchitis, hypertension, history of supraventricular tachycardia,, pulmonary nodules, hypercholesterolemia. Medications include Flovent 110 mcg 2 puffs twice daily, albuterol as needed, metoprolol tartrate 5 mg one daily, amlodipine 5 mg one daily, furosemide 10 mg one daily, Allegra 60 mg one daily, aspirin 81 mg one daily. Family history: no renal disease. Social history: remote tobacco abuse (quit 50 years ago), no alcohol or illicit drug use. Review of systems is unremarkable. Examination is notable for a BP of 164/84 mmHg, heart rate 70 beats/minute, respirations 20/minute, temperature 98.2, O2 saturation 99% on room air, but is otherwise negative.

Laboratory data shows: WBC 6.9, HCT 34.7%, Hb 11.9 g/dL, Platelets 207 thousands, Na 140 mEq/L, K 4.8 mEq/L, Gluc 92 g/dL, BUN 15, Cr 0.55 mg/dL. Urinalysis shows: color -dark yellow, leukocyte esterase trace, nitrate negative, protein 3+, blood 3+, WBC 10-15, RBC 60-70, bacteria 2+. A renal biopsy is performed.

What is the differential diagnosis and what is the biopsy likely to show?