MKSAP Quiz: Follow-up for elevated serum creatinine level
A 35-year-old man is evaluated during a follow-up visit for an elevated serum creatinine level discovered during a recent hospitalization for cellulitis of the right lower leg. He is a migratory agricultural worker. Following a physical exam, lab studies, and kidney ultrasound, what is the most likely diagnosis?
A 35-year-old man is evaluated during a follow-up visit for an elevated serum creatinine level. The elevated serum creatinine was discovered during a recent hospitalization for cellulitis of the right lower leg that was treated with intravenous cephazolin followed by oral cephalexin for a total of 7 days of antibiotic therapy. He is a migratory agricultural worker. He works in the northeastern United States during summer months and returns to Guatemala for the remainder of the year performing similar work. The patient has no other medical problems and takes no medications.
On physical examination, blood pressure is 138/90 mm Hg; other vital signs are normal. BMI is 27. The remainder of the examination is normal.
Laboratory studies:
| Creatinine | 2.0 mg/dL (176.8 µmol/L) |
| Electrolytes: | |
| Sodium | 140 mEq/L (140 mmol/L) |
| Potassium | 5.0 mEq/L (5.0 mmol/L) |
| Chloride | 112 mEq/L (112 mmol/L) |
| Bicarbonate | 18 mEq/L (18 mmol/L) |
| Urinalysis | Specific gravity 1.015; pH 6.5; no blood; 1+ protein; 1+ leukocytes; 2-5 leukocytes/hpf; 0-2 erythrocytes/hpf; no casts |
| Urine protein-creatinine ratio | 400 mg/g |
Kidney ultrasound shows a 9.9-cm right kidney and a 10.3-cm left kidney with increased cortical echogenicity and mild thinning; there is no hydronephrosis.
Which of the following is the most likely diagnosis?
A. Acute interstitial nephritis
B. Acute tubular necrosis
C. Chronic interstitial nephritis
D. IgA nephropathy
E. Infection-related glomerulonephritis
MKSAP Answer and Critique
The correct answer is C. Chronic interstitial nephritis. This content is available to MKSAP 19 subscribers as Question 24 in the Nephrology section. More information about MKSAP is available online.
Chronic interstitial nephritis (Option C) is the most likely diagnosis. Chronic interstitial nephritis in agricultural communities (CINAC; also known as Mesoamerican nephropathy) is an emerging public health problem in many Central American and Asian countries. It is observed most commonly in young- to middle-aged male migratory agricultural workers and often progresses to end-stage kidney disease. This patient has many findings associated with chronic tubulointerstitial kidney disease. He is hypertensive and has a normal anion gap metabolic acidosis. Furthermore, his urinalysis demonstrates pyuria and low-grade proteinuria, and his kidney ultrasound shows nonspecific chronic kidney injury changes (increased cortical echogenicity and mild thinning). These findings, in the context of a patient who is a migratory agricultural worker in Central America, suggest that he has developed CINAC. Kidney biopsy may establish a definitive diagnosis.
Acute interstitial nephritis (Option A) is characterized by urine sediment containing leukocytes and leukocyte casts, unlike this patient's relatively bland urine sediment.
Although patients with acute bacterial infection may occasionally present with acute tubular necrosis (Option B), these patients typically have features of a systemic inflammatory response syndrome at the time of presentation and urine sediment showing granular casts.
IgA nephropathy (Option D) is a chronic glomerular disease typically characterized by microhematuria and occasional episodes of gross hematuria. This patient has a chronic tubulointerstitial disorder, not a glomerular disorder.
Infection-related glomerulonephritis (Option E), which may be seen concurrent with or following cellulitis, is accompanied by erythrocytes and erythrocyte casts in the urine sediment and often resolves after the acute infection resolves.
Key Points
- Chronic interstitial nephritis in agricultural communities is most commonly observed in young- to middle-aged male agricultural workers and often progresses to end-stage kidney disease.
- Patients with chronic interstitial nephritis in agricultural communities may be hypertensive, and urinalysis may be normal or demonstrate pyuria and low-grade proteinuria.