* Abbreviations: ACE: : angiotensin converting enzyme CNIII: : cranial nerve III CNS: : central nervous system CSF: : cerebrospinal fluid CT: : computed tomography ESR: : erythrocyte sedimentation rate Ig: : immunoglobulin LN: : lupus nephritis RBC: : red blood cell SLE: : systemic lupus erythematosus TB: : tuberculosis WBC: : white blood cell A 14-year-old African American boy presents with fever, right-sided neck swelling, and weight loss of 20 lb over 2-month period. He denies night sweats, illness contacts, or recent travel. He was seen 1 month ago for fatigue, body aches, decreased appetite, and 10 lb weight loss over the previous month. Due to a family history of diabetes, urinalysis was performed, which revealed moderate hemoglobin, protein of 200 mg/dL, white blood cell (WBC) count of 13/high power field, and red blood cell (RBC) count of 5/high power field. He was scheduled to be re-evaluated in 1 week but has been lost to follow-up. The boy appears tired. His weight is 54.2 kg (>50th percentile), height is 165 cm (75th percentile), temperature is 38.9°C, heart rate is 106 beats/minute, respiratory rate is 20 breaths/minute, and blood pressure is 113/64 mm Hg. Physical examination reveals a 3 × 4 cm, tender, nonerythematous, nonfluctuant, slightly mobile right cervical mass located behind the sternocleidomastoid muscle. Findings on the rest of the examination are normal. Complete blood count reveals a WBC count of 5.5 × 103/μL, with 65% granulocytes, 30% lymphocytes, and 5% monocytes, platelet count of 267 × 103/μL, hemoglobin level 9.5 g/dL, hematocrit 29%, mean corpuscular volume 71 fL, RBC distribution width 15.2%, and normal peripheral smear. His erythrocyte sedimentation rate (ESR) is 65 mm/h, and C-reactive protein (CRP) level is 1.081 mg/dL. Metabolic panel reveals a sodium concentration of 141 mEq/L, potassium 4.5 mEq/L, chloride 111 mEq/L, bicarbonate 24 mEq/L, serum urea nitrogen 33 mg/dL, creatinine 1.7 mg/dL, total protein 6 g/dL, and albumin 1.9 g/dL. Urinalysis reveals a protein of 200 mg/dL and rare granular casts. Chest radiograph is normal. Blood and urine cultures are obtained, and a tuberculin test is performed on admission. Additional evaluation reveals the …