MKSAP Quiz: Evaluation of an elevated serum creatinine level
A 71-year-old man is evaluated in the hospital for an elevated serum creatinine level. He was hospitalized 2 days ago for a 4-day history of progressive right lower leg cellulitis. History is also significant for type 2 diabetes mellitus with prior episodes of cellulitis. Following a physical exam, lab studies, and a kidney biopsy, what is the most likely cause of this patient's kidney disease?
A 71-year-old man is evaluated in the hospital for an elevated serum creatinine level. He was hospitalized 2 days ago for a 4-day history of progressive right lower leg cellulitis. History is also significant for type 2 diabetes mellitus with prior episodes of cellulitis. Medications are basal and prandial insulin.
On physical examination, temperature is 38.9 °C (102.0 °F), blood pressure is 150/100 mm Hg, pulse rate is 100/min, and respiration rate is 20/min. A well-defined area of tender erythema and edema is present over the right foot and leg to just below the knee. The remainder of the examination is unremarkable.
Laboratory studies:
| Leukocyte count | 13,500/µL (13.5 × 109/L) |
| C3 | 50 mg/dL (500 mg/L) |
| C4 | 12 mg/dL (120 mg/L) |
| Creatinine | On admission: 2.4 mg/dL (212.2 µmol/L); baseline: 1.1 mg/dL (97.2 µmol/L) |
| Urinalysis | 3+ blood; 3+ protein |
| Urine protein-creatinine ratio | 4100 mg/g |
Kidney biopsy shows endocapillary proliferation on light microscopy, co-dominant granular staining for C3 and IgA on immunofluorescence microscopy, and subepithelial hump-like deposits on electron microscopy.
Which of the following is the most likely cause of this patient's kidney disease?
A. Staphylococcus aureus
B. Streptococcus agalactiae
C. Streptococcus pneumoniae
D. Streptococcus pyogenes
MKSAP Answer and Critique
The correct answer is A. Staphylococcus aureus. This content is available to MKSAP 18 subscribers as Question 77 in the Nephrology section. More information about MKSAP is available online.
Staphylococcus aureus is the most likely cause of this patient's infection-related glomerulonephritis (IRGN). This patient has acute kidney injury in the setting of cellulitis, with active urine sediment and low serum complement levels. The biopsy shows a proliferative glomerulonephritis on light microscopy with immunofluorescence of C3 and IgA and subepithelial hump-like deposits on electron microscopy, confirming a diagnosis of IRGN. In the developed world, the epidemiology of IRGN has drastically shifted over the past few decades, moving away from streptococcal-associated glomerulonephritides to infections caused primarily by S. aureus and, at a significantly lower rate, gram-negative bacteria. In this patient with cellulitis and IRGN occurring at the time of infection, S. aureus is the most likely culprit pathogen.
In patients with poststreptococcal glomerulonephritis (group A Streptococcus, or Streptococcus pyogenes), there is a latent period between the resolution of the streptococcal infection and the acute onset of the nephritic syndrome, usually 7 to 10 days after oropharyngeal infections and 2 to 4 weeks after skin infections. In adults with non-poststreptococcal IRGN, the glomerulonephritis often coexists with the triggering infection. Sites of infection can include the upper and lower respiratory tract, skin/soft tissue, bone, teeth/oral mucosa, heart, deep abscesses, shunts, and indwelling catheters. Notably, this patient's kidney failure has occurred at the same time as the cellulitis, consistent with a staphylococcal-mediated form of IRGN.
Streptococcus pneumoniae is an uncommon cause of cellulitis, and Streptococcus agalactiae (group B Streptococcus) is capable of causing cellulitis in nonpregnant adults in special circumstances (lymphedema, vascular insufficiency, chronic dermatitis, or radiation-induced cutaneous injury). S. pyogenes and S. aureus are much more common causes of cellulitis, and the co-occurrence of the infection and IRGN points to S. aureus as the most likely culprit.
Key Point
- In adults, most cases of infection-related glomerulonephritis are no longer poststreptococcal, and the glomerulonephritis often coexists with the triggering infection.