What is the cause of a patient's acute kidney injury with significant lymphadenopathy, given a history of stage 3a Chronic Kidney Disease (CKD), recent onset of inguinal bruising, and blood in stools, with imaging showing right hydroureteronephrosis and lymphadenopathy?

Acute-on-Chronic Kidney Disease with Obstructive Uropathy Secondary to Malignant Lymphadenopathy

This patient has acute kidney injury (AKI) superimposed on chronic kidney disease (CKD), with obstructive uropathy from retroperitoneal and iliac lymphadenopathy causing right hydroureteronephrosis, and the clinical presentation strongly suggests an underlying lymphoproliferative malignancy (likely lymphoma) causing both the obstruction and systemic manifestations (inguinal bruising, gastrointestinal bleeding). 1

Understanding the Kidney Injury Pattern

The dramatic deterioration in kidney function over three months represents AKI on CKD:

• Baseline CKD Stage 3a: GFR 53 mL/min, creatinine 1.34 mg/dL, BUN 18 mg/dL 2
• Current presentation: GFR 11 mL/min (Stage 5/kidney failure), creatinine 4.99 mg/dL, BUN 50 mg/dL—representing a >3-fold increase in creatinine, meeting Stage 3 AKI criteria 1, 3
• This acute deterioration lasting less than 3 months qualifies as acute kidney disease (AKD), which carries significantly increased mortality risk when combined with underlying CKD 1

The Obstructive Component

The right hydroureteronephrosis with distal ureteral obstruction is a critical, potentially reversible cause of the AKI that requires urgent intervention. 3

• Obstructive uropathy must be identified and relieved promptly, as persistent obstruction leads to irreversible kidney damage 3
• Renal ultrasound has appropriately identified hydronephrosis and the level of obstruction 3
• The extensive retroperitoneal and bilateral iliac lymphadenopathy is compressing the distal right ureter, causing the obstruction 3

The Underlying Malignancy

The constellation of findings points strongly toward lymphoma:

• Massive lymphadenopathy: Retroperitoneal and bilateral iliac chains causing ureteral compression 3
• Inguinal bruising: Suggests either direct lymph node involvement, coagulopathy from bone marrow infiltration, or thrombocytopenia 1
• Gastrointestinal bleeding: May indicate gastrointestinal tract involvement by lymphoma or bleeding diathesis 1
• The rapid progression over 3 months is consistent with aggressive lymphoproliferative disease 2

Immediate Management Priorities

Urgent urologic intervention to relieve the obstruction is the first priority, as this is the only potentially reversible component of the kidney injury. 3

1. Relief of Obstruction

• Nephrostomy tube placement or ureteral stent insertion should be performed emergently to decompress the obstructed kidney 3
• This intervention may partially restore kidney function, though complete recovery is unlikely given the severity and duration of obstruction 3
• Monitor for post-obstructive diuresis after relief, which can cause volume depletion and electrolyte abnormalities requiring aggressive fluid replacement 3

2. Establish Malignancy Diagnosis

• Lymph node biopsy (inguinal or image-guided retroperitoneal) is essential to confirm lymphoma and determine subtype 2
• Complete blood count may reveal cytopenias from bone marrow involvement 2
• Lactate dehydrogenase (LDH) is typically elevated in lymphoma 2
• Flow cytometry and immunohistochemistry on biopsy tissue will guide treatment 2

3. Address Acute Kidney Complications

• Avoid nephrotoxic medications during this critical period 3
• Monitor electrolytes closely, particularly potassium and phosphorus, as Stage 5 kidney disease carries risk of life-threatening hyperkalemia 1, 2
• Assess volume status carefully—patients may be volume overloaded from kidney failure or volume depleted from bleeding 1
• Serial creatinine measurements will track recovery after obstruction relief 3

4. Manage Bleeding

• Assess coagulation parameters and platelet count 1
• Type and cross-match blood products if transfusion is needed 1
• Endoscopy may be required to identify and treat gastrointestinal bleeding source 1

Renal Replacement Therapy Considerations

If the patient develops life-threatening complications (severe hyperkalemia, volume overload with pulmonary edema, uremic symptoms, or severe metabolic acidosis), urgent dialysis is indicated regardless of the underlying cause. 1, 3

• Stage 3 AKI with GFR 11 mL/min places this patient at high risk for dialysis requirement 1
• However, relief of obstruction should be attempted first, as partial recovery may obviate dialysis need 3
• Nephrology consultation is mandatory given the severity of kidney injury and complexity of management 3

Prognosis and Long-term Implications

The combination of AKI on CKD (AKD with underlying CKD) carries the highest risk of progression to end-stage kidney disease and death. 1

• Even with successful obstruction relief and lymphoma treatment, complete kidney function recovery is unlikely given the severity and duration of injury 1, 4, 5
• The patient will likely progress to advanced CKD or end-stage renal disease requiring long-term dialysis or transplantation 4, 5
• Survival depends heavily on the lymphoma subtype, stage, and response to chemotherapy 2

Critical Pitfalls to Avoid

• Do not delay obstruction relief while pursuing malignancy workup—these should proceed in parallel, as every hour of continued obstruction causes irreversible nephron loss 3
• Do not use eGFR equations (MDRD, CKD-EPI) during AKI, as they are inaccurate in non-steady-state conditions 3
• Do not assume kidney function will fully recover after obstruction relief—this patient has sustained significant injury and requires long-term nephrology follow-up 1, 3
• Avoid contrast-enhanced CT for further imaging given the severe kidney dysfunction, unless absolutely necessary for urgent surgical planning 2
• Recognize that chemotherapy for lymphoma will need dose adjustments for kidney function and may further compromise renal function 2

Follow-up Strategy

After acute management, this patient requires:

• Nephrology follow-up at 3 months post-discharge to assess for progression to CKD or incomplete recovery from AKD 1, 3
• Oncology management for lymphoma treatment with careful attention to nephrotoxic chemotherapy agents 2
• Monitoring for recurrent obstruction if lymphoma responds slowly to treatment 3
• Blood pressure control and medication reconciliation, avoiding nephrotoxic agents 1, 3