Part A: Clinical information
Gender, Age
Male, 27 years old
Previous illnesses
None
Time period since the onset of the first symptoms
Relatively short: patient presented with a combination of malaise and arthralgia to his general physician and a rapidly progressive AKI was soon detected after which the patient was referred to a nephrologist.
Presentation
Combination of arthralgia, urticaria, slight temperature elevation and rapidly progressive AKI.
Laboratory parameters
Proteinuria: 1.0 grams
Positive urine sediment, erythrocyturia
ANCA, anti-GBM, anti-ds DNA negative.
Why was the decision made for a biopsy?
AKI of unknown cause.
How long after the first symptoms was the biopsy conducted?
Approximately 1 month.
Suspected diagnosis of the indication for biopsy?
The clinical question was: explanation for renal insufficiency?
Note related to annotations: To avoid obscuring the lesions, the annotations are deliberately positioned close to, but not directly over, the lesion areas.
Part B: Kidney biopsy findings
Description of light microscopy:
Kidney biopsy with cortical tissue and medulla, and approximately 12 glomeruli. No global glomerulosclerosis. Glomeruli show a variety of lesions: some show slight mesangial expansion; others have mesangial sclerosis and one has an FSGS (focal segmental glomerulosclerosis) lesion. There is also a glomerulus with a circumferential cellular crescent and endocapillary hypercellularity. A minority of glomeruli is normal. Throughout the biopsy there is quite some IFTA (interstitial fibrosis & tubular atrophy), approximately 30% and moderately associated with mild mononuclear infiltrate. Vessels are normal.
Immunofluorescence:
IF: 3+ positivity mainly in mesangial areas of C3. Other staining (IgA, IgG, IgM, C1q and light chains) are negative.
Electron Microscopy (EM):
EM shows numerous translucent deposits in the mesangial areas.
Considerations:
In this patient, the diagnosis of C3G was unexpected. The IF in combination with EM are characteristic of C3G. C3G has a variable pattern by light microscopy and in this particular case, the findings are also variable within the biopsy. On the one hand, there are active lesions in the form of the crescent and endocapillary hypercellularity. However, there is also a background of chronic lesions with quite some interstitial fibrosis, an FSGS lesion and mesangial sclerosis. Perhaps the patient went through previous episodes of C3G that went by unnoticed. It is unlikely that the chronic changes were caused by another disease – but as they are fairly non-specific, this option cannot be completely ruled out either.