A broad term encompassing histomorphological patterns and disease processes/entities, affecting primarily the glomeruli. Despite the name, inflammation is not necessarily a feature in many of these disease and glomerulonephropathy might be a better term.
The classification and disease labels are confusing as some terms may refer to histological patterns as well as disease. A specific pattern can be caused by various diseases and, conversely, a single disease can give rise to numerous patterns.
Even the terms primary and secondary are sometimes used unintuitively. For instances, 70-80% of primary membranous nephropathy are due to auto-antibodies against the PLA2-R, but despite an identifiable cause, the 'primary' label still persists. Similarly, in focal segmental glomerulosclerosis, there are numerous known mutations in filtration-related proteins that are still considered to be 'primary' FSGS.
Many disease labels are based on the histomorphological pattern seen on light microscopy, but more precise diagnosis often requires special stains, immunohistochemistry/immunofluorescence, electron microscopy and close correlation with clinical details. For instance, a history of haematuria with normal glomerular morphology could be due to genuinely normal kidney, IgA nephropathy or thin basement membrane disease.
Classification is complex and sometimes confusing for the reasons alluded to above. Typically a morphological description is provided, which when combined with ancillary tests and clinical information, allows a more specific label to be provided, or at worst a narrower list of possible diagnoses.
The morphological patterns are typically based on which part of the glomerulus is damaged (see below), but many renal physicians and pathologists approach the disease entities by considering the clinical picture (age, urinalysis, serology etc).
- Nephrotic syndrome
- Nephritic syndrome
- Isolated haematuria
- Renal failure
- Acute kidney injury
- If rapidly progressive, then labelled rapidly progressive glomerulonephritis
- Acute on chronic renal failure
Normal could be:
- Minimal change nephropathy
- Early membranous nephropathy
- Focal segmental glomerulosclerosis, but no sclerotic glomeruli sampled.
Glomerular basement membrane
- Nodular sclerosis: may be due to diabetic nephropathy, light chain deposition
- Focal segmental glomerulosclerosis, multiple variants