Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.
A 54-year-old woman is evaluated for fatigue, anorexia, polyuria, and nocturia of several weeks’ duration. She had otherwise felt well until the onset of her current symptoms. Medical history is significant for autoimmune pancreatitis diagnosed 1 year ago, treated with a prednisone taper that was completed 8 months ago with resolution of her symptoms. She takes no medications.
On physical examination, temperature is 36.2 °C (97.2 °F), blood pressure is 110/58 mm Hg, pulse rate is 72/min, and respiration rate is 16/min. BMI is 25. Estimated central venous pressure is 7 cm H2O. The lungs are clear. There are no murmurs or extra heart sounds. Abdominal examination is unremarkable. There is no edema.
Laboratory studies:
| Blood urea nitrogen | 56 mg/dL (20 mmol/L) |
| Creatinine | 5.2 mg/dL (459.7 µmol/L) |
| Serum free light chain ratio | Normal |
| Urinalysis | pH 5.0; 1+ protein; 3-5 erythrocytes/hpf; 5-10 leukocytes/hpf; occasional leukocyte casts |
Chest radiograph is normal. Kidney ultrasound shows slightly enlarged kidneys without evidence of obstruction.
Which of the following is the most likely diagnosis?
A: ANCA-associated vasculitis
B: Anti–glomerular basement membrane antibody disease
C: IgG4-related interstitial nephritis
D: Lupus nephritis
MKSAP Answer and Critique
The correct answer is C: IgG4-related interstitial nephritis.
The most likely diagnosis is IgG4-related interstitial nephritis. This patient has a history of autoimmune pancreatitis and now presents with acute kidney injury. Her urinalysis is most consistent with a tubulointerstitial pattern, with mild proteinuria and the presence of inflammatory cells. This history and clinical presentation suggest the possibility of IgG4-related interstitial nephritis. Systemic IgG4-related disease is an uncommon disorder characterized by infiltration of different organs by lymphoplasmacytic infiltrates of IgG4-positive plasma cells with resultant fibrosis associated with elevated serum IgG4 levels. Autoimmune pancreatitis is one form of IgG-related disease, although other organs such as the kidney may be affected, most commonly as interstitial nephritis. IgG4-related interstitial nephritis may present with acute or chronic kidney failure as well as renal mass–like lesions on imaging. As with other IgG4-related diseases, almost all patients with IgG4-related kidney disease will have elevated serum IgG4 levels, and the kidneys may be diffusely enlarged on imaging due to cellular infiltration. Definitive diagnosis requires kidney biopsy with staining for IgG4-positive plasma cells. Treatment is similar to other IgG4-related diseases using immunosuppression with glucocorticoids.
ANCA-associated vasculitis and anti–glomerular basement membrane antibody disease typically cause rapidly progressive glomerulonephritis with significant proteinuria and hematuria in the sediment, occasionally with erythrocyte casts, none of which is present in this patient.
Lupus nephritis is primarily a glomerular lesion with significant proteinuria in the context of other clinical findings suggestive of systemic lupus erythematosus. This patient’s clinical presentation is therefore less consistent with this diagnosis.
Key Point
- IgG4-related disease is characterized by infiltration of different organs by lymphoplasmacytic infiltrates of IgG4-positive plasma cells with resultant fibrosis associated with elevated serum IgG4 levels.
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